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INTERNET-DRAFT                                         M Cieslak
<draft-wilson-wrec-wccp-v2-01.txt>                     D Forster
                                                       G Tiwana
                                                       R Wilson
                                                       Cisco Systems
                                                       03 Apr 2001
                                                       Expires Oct 2001

                 Web Cache Communication Protocol V2.0

Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
   provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference material
   or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/lid-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

1. Abstract

   This document describes version 2.0 of the Web Cache Communication
   Protocol (WCCP). The WCCP V2.0 protocol specifies interactions between
   one or more routers and one or more web-caches. The purpose of the
   interaction is to establish and maintain the transparent redirection
   of selected types of traffic flowing through a group of routers. The
   selected traffic is redirected to a group of web-caches with the aim
   of optimising resource usage and lowering response times.

   The protocol does not specify any interaction between the web-caches
   within a group or between a web-cache and a web-server.

2. Definitions

   Assignment Method

      The method by which redirected packets are distributed between



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web-caches.

   Designated Web-Cache.

      The web-cache in a web-cache farm responsible for dictating to the
      router or routers how redirected traffic should be distributed between
      the members of the farm.

   Forwarding Method

      The method by which redirected packets are transported from router to
      web-cache.

   Packet Return Method

      The method by which packets redirected to a web-cache are returned to
      a router for normal forwarding.

   Redirection Hash Table.

      A 256-bucket hash table maintained by the router or routers. This
      table maps the hash index derived from a packet to be redirected to
      the IP address of a destination web-cache.

   Service Group

      A group of one or more routers plus one or more web-caches working
      together in the redirection of traffic whose characteristics are part
      of the Service Group definition.

   Transparent Redirection.

      Transparent redirection is a technique used to deploy caching without
      the need for reconfiguration of clients or servers. It involves the
      interception and redirection of traffic to one or more web-caches by a
      router or switch transparently to the end points of the traffic flow.

   Usable Web-Cache.

      From the viewpoint of a router a web-cache is considered a usable
      member of a Service Group when it has sent that web-cache a
      WCCP2_I_SEE_YOU message and has received in response a WCCP2_HERE_I_AM
      message with a valid "Receive ID".

   Web-Cache Farm.

      One or more web-caches associated with a router or routers.




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3. Introduction

3.1 Protocol Overview

   WCCP V2.0 defines mechanisms to allow one or more routers enabled for
   transparent redirection to discover, verify, and advertise
   connectivity to one or more web-caches.

   Having established connectivity the routers and web-caches form
   Service Groups to handle the redirection of traffic whose
   characteristics are part of the Service Group definition.

   The protocol provides the means to negotiate the specific method
   used for load distribution among web-caches and also the method used
   to transport traffic between router and cache.

   A single web-cache within a Service Group is elected as the designated
   web-cache. It is the responsibility of the designated web-cache to
   provide routers with the data which determines how redirected traffic
   is distributed between the web-caches in the Service Group.

3.2 WCCP V2.0 enhancements

   WCCP V2.0 supports the following enhancements to the WCCP V1.0
   protocol.

   * Multi-Router Support.
   WCCP V2.0 allows a farm of web-caches to be attached to more than one
   router.

   * Multicast Support.
   WCCP V2.0 supports multicasting of protocol messages between
   web-caches and routers.

   * Improved Security.
   WCCP V2.0 provides optional authentication of protocol packets
   received by web-caches and routers.

   * Support for redirection of non-HTTP traffic.
   WCCP V2.0 supports the redirection of traffic other than HTTP traffic
   through the concept of Service Groups.

   * Packet return.
   WCCP V2.0 allows a web-cache to decline to service a redirected packet
   and to return it to a router to be forwarded. The method by which
   packets are returned to a router is negotiable.





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* Alternative Hashing.
   WCCP V2.0 allows the designated web-cache to mark individual buckets
   in the Redirection Hash Table for a secondary hash. This allows the
   traffic being hashed to a particular bucket to be distributed across
   the members of a Service Group.

   * Multiple Forwarding Methods
   WCCP V2.0 allows individual web-caches to negotiate the method by
   which packets are forwarded to a web-cache from a router. Packets
   may now be forwarded unencapsulated using a Layer 2 destination
   address rewrite.

   * Multiple Assignment Methods
   WCCP V2.0 allows the designated web-cache to negotiate the method by which
   packets are distributed between the web-caches in a service group.
   Packets may now be assigned using a hashing scheme or a masking scheme.

   * Command and Status Information
   WCCP V2.0 includes a mechanism to allow a web-cache to pass a command
   to the routers in a Service Group. The same mechanism can be employed
   by the routers to pass status information to the web-caches in a
   Service Group.

4. Protocol Description

4.1 Joining a Service Group

   A web-cache joins and maintains its membership of a Service Group by
   transmitting a WCCP2_HERE_I_AM message to each router in the Group at
   HERE_I_AM_T (10) second intervals. This may be by unicast to each
   router or multicast to the configured Service Group multicast
   address. The Web Cache Info component in the WCCP2_HERE_I_AM message
   identifies the web-cache by IP address. The Service Info component of
   the WCCP2_HERE_I_AM message identifies and describes the Service Group in
   which the web-cache wishes to participate.

   A router responds to a WCCP2_HERE_I_AM message with a WCCP2_I_SEE_YOU
   message. If the WCCP2_HERE_I_AM message was unicast then the router will
   respond immediately with a unicast WCCP2_I_SEE_YOU message. If the
   WCCP2_HERE_I_AM message was multicast the router will respond via the
   scheduled multicast WCCP2_I_SEE_YOU message for the Service Group.

   A router responds to multicast web-cache members of a Service Group
   using a multicast WCCP2_I_SEE_YOU message transmitted at 9 second
   intervals with a 10% jitter.

   The Router Identity component in a WCCP2_I_SEE_YOU message includes a list
   of the web-caches to which the packet is addressed. A web-cache not



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in the list should discard the WCCP2_I_SEE_YOU message.

4.2 Describing a Service Group

   The Service Info component of a WCCP2_HERE_I_AM message describes the
   Service Group in which a web-cache wishes to participate. A Service
   Group is identified by Service Type and Service ID. There are two
   types of Service Group:

   * Well Known Services
   * Dynamic Services.

   Well Known Services are known by both routers and web-caches and do
   not require a description other than a Service ID.

   In contrast Dynamic Services must be described to a router. A router
   may be configured to participate in a particular Dynamic Service
   Group, identified by Service ID, without any knowledge of the
   characteristics of the traffic associated with the Service Group. The
   traffic description is communicated to the router in the
   WCCP2_HERE_I_AM message of the first web-cache to join the Service
   Group. A web-cache describes a Dynamic Service using the Protocol,
   Service Flags and Port fields of the Service Info component. Once a
   Dynamic Service has been defined a router will discard any subsequent
   WCCP2_HERE_I_AM message which contains a conflicting description. A
   router will also discard a WCCP2_HERE_I_AM message which describes a
   Service Group for which the router has not been configured.

4.3 Establishing Two-Way Connectivity

   WCCP V2.0 uses a "Receive ID" to verify two-way connectivity between a
   router and a web-cache.  The Router Identity Info component of a
   WCCP2_I_SEE_YOU message contains a "Receive ID" field. This field is
   maintained separately for each Service Group and its value is
   incremented each time the router sends a WCCP2_I_SEE_YOU message to
   the Service Group.

   The "Receive ID" sent by a router is reflected back by a web-cache in
   the Web-Cache View Info component of a WCCP2_HERE_I_AM message. A
   router checks the value of the "Receive ID" in each WCCP2_HERE_I_AM
   message received from a Service Group member. If the value does not
   match the "Receive ID" in the last WCCP2_I_SEE_YOU message sent to
   that member the message is discarded.

   A router considers a web-cache to be a usable member of a Service
   Group only after it has sent that web-cache a WCCP2_I_SEE_YOU message
   and received a WCCP2_HERE_I_AM message with a valid "Receive ID" in
   response.



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4.4 Negotiating the Forwarding Method

   A web-cache and router may negotiate the method by which packets are
   forwarded to the web-cache by the router.

   This negotiation is per web-cache, per Service Group. Thus web-caches
   participating in the same Service Group may negotiate different
   forwarding methods with the Service Group routers.

   A router will advertise the supported forwarding methods for a Service
   Group using the optional Capabilities Info component of the
   WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
   the router supports the default GRE encapsulation method only.

   A web-cache will inspect the forwarding method advertisement in the
   first WCCP2_I_SEE_YOU message received from a router for a particular
   Service Group. If the router does not advertise a method supported by
   the web-cache then the web-cache will abort its attempt to join the
   Service Group. Otherwise the web-cache will pick one method from those
   advertised by the router and specify that in the optional Capabilities
   Info component of its next WCCP2_HERE_I_AM message. Absence of a
   forwarding method advertisement in a WCCP2_HERE_I_AM message implies
   the cache is requesting the default GRE encapsulation method.

   A router will inspect the forwarding method selected by a web-cache in
   the WCCP2_HERE_I_AM message received in response to a WCCP2_I_SEE_YOU
   message. If the selected method is not supported by the router the
   router will ignore the WCCP2_HERE_I_AM message. If the forwarding
   method is supported the router will accept the web-cache as usable and
   add it to the Service Group.

4.5 Negotiating the Assignment Method

   A web-cache and router may negotiate the method by which packets are
   distributed between the web-caches in a Service Group.

   The negotiation is per Service. Thus web-caches participating in
   several Service Groups may negotiate a different assignment method for
   each Service Group.

   A router will advertise the supported assignment methods for a
   Service Group using the optional Capabilities Info component of the
   WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
   the router supports the default Hash assignment method only.

   A web-cache will inspect the assignment method advertisement in the
   first WCCP2_I_SEE_YOU message received from a router for the Service
   Group. If the router does not advertise a method supported by the



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web-cache then the web-cache will abort its attempt to join the
   Service Group. Otherwise the web-cache will pick one method from those
   advertised by the router and specify that in the optional Capabilities
   Info component of its next WCCP2_HERE_I_AM message. Absence of an
   assignment method advertisement in a WCCP2_HERE_I_AM message implies
   the cache is requesting the default Hash assignment method.

   A router will inspect the assignment method selected by a web-cache in
   the WCCP2_HERE_I_AM message received in response to a WCCP2_I_SEE_YOU
   message. If the selected method is not supported by the router the
   router will ignore the WCCP2_HERE_I_AM message. If the assignment
   method is supported the router will accept the web-cache as usable and
   add it to the Service Group.

4.5 Negotiating the Packet Return Method

   A web-cache and router may negotiate the method by which packets are
   returned from a web-cache to a router for normal forwarding.

   The negotiation is per Service. Thus web-caches participating in
   several Service Groups may negotiate a different packet return method
   for each Service Group.

   A router will advertise the supported packet return methods for a
   Service Group using the optional Capabilities Info component of the
   WCCP2_I_SEE_YOU message. The absence of such an advertisement implies
   the router supports the default GRE packet return method only.

   A web-cache will inspect the packet return method advertisement in the
   first WCCP2_I_SEE_YOU message received from a router for the Service
   Group. If the router does not advertise a method supported by the
   web-cache then the web-cache will abort its attempt to join the
   Service Group. Otherwise the web-cache will pick one method from those
   advertised by the router and specify that method in the optional
   Capabilities Info component of its next WCCP2_HERE_I_AM
   message. Absence of a packet return method advertisement in a
   WCCP2_HERE_I_AM message implies the cache is requesting the default
   GRE packet return method.

   A router will inspect the packet return method selected by a web-cache
   in the WCCP2_HERE_I_AM message received in response to a
   WCCP2_I_SEE_YOU message. If the selected method is not supported by
   the router the router will ignore the WCCP2_HERE_I_AM message. If the
   packet return method is supported the router will accept the web-cache
   as usable and add it to the Service Group.






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4.6 Advertising Views of the Service Group

   Each router advertises its view of a Service Group via the Router View
   Info component in the WCCP2_I_SEE_YOU message it sends to web-caches.
   This component includes a list of the useable web-caches in the
   Service Group as seen by the router and a list of the routers in the
   Service Group as reported in WCCP2_HERE_I_AM messages from
   web-caches. A change number in the component is incremented if the
   Service Group membership has changed since the last WCCP2_I_SEE_YOU
   message sent by the router.

   Each web-cache advertises its view of the Service Group via the Web
   Cache View Info component in the WCCP2_HERE_I_AM message it sends to
   routers in the Service Group. This component includes the list of
   routers that have sent the web-cache a WCCP2_I_SEE_YOU message and a
   list of web-caches learnt from the WCCP2_I_SEE_YOU messages. The Web
   Cache View Info component also includes a change number which is
   incremented each time Service Group membership information changes.

4.7 Security

   WCCP V2.0 provides a security component in each protocol message to
   allow simple authentication.  Two options are supported:

   * No Security (default)
   * MD5 password security

   MD5 password security requires that each router and web-cache wishing
   to join a Service Group be configured with the Service Group
   password. Each WCCP protocol packet sent by a router or web-cache for
   that Service Group will contain in its security component the MD5
   checksum of the WCCP protocol message (including the WCCP message
   header) and a Service Group password. Each web-cache or router in the
   Service Group will authenticate the security component in a received
   WCCP message immediately after validating the WCCP message header.
   Packets failing authentication will be discarded.

4.8 Distribution of Traffic Assignments

   WCCP V2.0 allows the traffic assignment method to be negotiated. There
   are two types of information to be communicated depending on the
   assignment method:

   * Hash Tables
   * Mask/Value Sets






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4.8.1 Hash Tables

   When using hash assignment each router uses a 256-bucket Redirection
   Hash Table to distribute traffic for a Service Group across the member
   web-caches. It is the responsibility of the Service Group's designated
   web-cache to assign each router's Redirection Hash Table.

   The designated web-cache uses a WCCP2_REDIRECT_ASSIGNMENT message to
   assign the routers' Redirection Hash Tables. This message is
   generated following a change in Service Group membership and is sent
   to the same set of addresses to which the web-cache sends WCCP2_HERE_I_AM
   messages. The designated web-cache will wait 1.5 HERE_I_AM_T
   seconds following a change before generating the message in order to
   allow the Service Group membership to stabilise.

   The Redirection Hash Tables can be conveyed in either an Assignment
   Info Component or an Alternate Assignment Component within a
   WCCP2_REDIRECT_ASSIGNMENT.  Both components contain an Assignment
   Key. This will be reflected back to the designated web-cache in
   subsequent WCCP2_I_SEE_YOU messages from the routers in the Service
   Group. A WCCP2_REDIRECT_ASSIGNMENT may be repeated after HERE_I_AM_T
   seconds if inspection of WCCP2_I_SEE_YOU messages indicates a router
   has not received an assignment.

   A router will flush its Redirection Hash Table if a
   WCCP2_REDIRECT_ASSIGNMENT is not received within 5 HERE_I_AM_T seconds
   of a Service Group membership change.  A router will flush its
   Redirection Hash Table if it receives a WCCP2_REDIRECT_ASSIGNMENT
   message in which it is not listed.

   The designated web-cache lists the web-caches to which traffic should
   be distributed in either an Assignment Info Component or an Alternate
   Assignment Component within a WCCP2_REDIRECT_ASSIGNMENT message. Only
   those web-caches seen by every router in the Service Group are
   included.

4.8.2 Mask/Value Sets

   When using mask assignment each router uses masks and a table of
   values to distribute traffic for a Service Group across the member
   web-caches. It is the responsibility of the Service Group's designated
   web-cache to assign each router's mask/value sets.

   The designated web-cache uses the Alternate Assignment Component in a
   WCCP2_REDIRECT_ASSIGNMENT message to assign the routers' mask/value
   set. This message is generated following a change in Service Group
   membership and is sent to the same set of addresses to which the
   web-cache sends WCCP2_HERE_I_AM messages. The designated web-cache



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will wait 1.5 HERE_I_AM_T seconds following a change before generating
   the message in order to allow the Service Group membership to
   stabilise.

   The Alternate Assignment Info component of the
   WCCP2_REDIRECT_ASSIGNMENT contains an Assignment Key. This will be
   reflected back to the designated web-cache in subsequent
   WCCP2_I_SEE_YOU messages from the routers in the Service Group. A
   WCCP2_REDIRECT_ASSIGNMENT message may be repeated after HERE_I_AM_T
   seconds if inspection of WCCP2_I_SEE_YOU messages indicates a router
   has not received an assignment.

   A router will flush its mask/value set if a WCCP2_REDIRECT_ASSIGNMENT
   is not received within 5 HERE_I_AM_T seconds of a Service Group
   membership change. A router will flush its mask/value set if it
   receives a WCCP2_REDIRECT_ASSIGNMENT in which it is not listed.

   The designated web-cache lists the web-caches to which traffic should
   be distributed in the Alternate Assignment Info component of the
   WCCP2_REDIRECT_ASSIGNMENT message. Only those web-caches seen by every
   router in the Service Group are included.

4.9  Electing the Designated Web-cache

   Election of the designated web-cache will take place once a Service
   Group membership has stabilised following a change. The designated
   web-cache must be receiving a WCCP2_I_SEE_YOU message from every
   router in the Service Group.

   Election of the designated web-cache is not part of the WCCP
   protocol. However it is recommended that the web-cache with the lowest
   IP address is selected as designated web-cache for a Service Group.

4.10 Traffic Interception

   A router will check packets passing through it against its set of
   Service Group descriptions. The Service Group descriptions are
   checked in priority order. A packet which matches a Service Group
   description is a candidate for redirection to a web-cache in the
   Service Group.

   A router will not redirect a packet with a source IP address matching
   any web-cache in the Service Group.








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4.11 Traffic Redirection

4.11.1 Redirection with Hash Assignment

   Redirection with hash assignment is a two-stage process. In the first
   stage a primary key is formed from the packet (as defined by the
   Service Group description) and hashed to yield an index into the
   Redirection Hash Table.

   If the Redirection Hash Table entry contains an unflagged web-cache
   index then the packet is redirected to that web-cache. If the bucket
   is unassigned the packet is forwarded normally. If the bucket is
   flagged as requiring a secondary hash then a secondary key is formed
   (as defined by the Service Group description) and hashed to yield an
   index into the Redirection Hash Table. If the secondary entry contains
   a web-cache index then the packet is directed to that web-cache. If the
   entry is unassigned the packet is forwarded normally.

4.11.2 Redirection with Mask Assignment

   The first step in redirection using the mask assignment method is to
   perform a bitwise AND operation between the mask from the first
   mask/value set in the Service Group definition and the contents of the
   packet. The output of this operation is the set of fields in the packet
   which will be used for value matching. The selected fields from the
   packet are then compared against each entry in the list of values for
   that mask/value set. If a match is found the packet is redirected to
   the web-cache associated with the value entry. If no match is found
   the process is repeated for each mask/value set defined for the
   Service Group.  If, after trying all of the mask/value sets defined
   for the Service Group, no match is found, the packet is forwarded
   normally.

   Mask/value sets are processed in the order in which they are
   presented in the Alternate Assignment component. Value elements are
   compared in the order in which they appear in the mask/value set of which
   they are part.

4.12 Traffic Forwarding

   WCCP allows the negotiation of the forwarding method between router
   and web-cache (See Negotiating the Forwarding Method). The currently
   defined forwarding methods are:

   * GRE Encapsulated
   * Unencapsulated with L2 rewrite





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4.12.1 Forwarding with GRE Encapsulation

   Redirected packets are encapsulated in a new IP packet with a GRE [1]
   header followed by a four-octet Redirect header.

   The GRE encapsulation uses the simple four-octet GRE header with the
   two Flags and Version octets set to zero and a Protocol Type of
   0x883E.

   The Redirect header is as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |D|A| Reserved  |  Service ID   |  Alt Bucket   |  Pri Bucket   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   D       Dynamic Service
           0: Well known service
           1: Dynamic service

   A       Alternative bucket used
           0: Primary bucket used
           1: Alternative bucket used

   Service ID

      Service Group identifier

   Alt Bucket

      Alternative bucket index used to redirect the packet. Only valid
      for hash assignment.

   Pri Bucket

      Primary bucket index used to redirect the packet. Only valid for hash
      assignment.

4.12.2 Forwarding with L2 Rewrite

   Redirected packets are not encapsulated. The router replaces the
   packet's destination MAC address with the MAC address of the target
   web-cache.

   This forwarding method requires that the target web-cache
   be directly-connected to the router at Layer 2. A router will not
   allow a web-cache which is not directly attached to negotiate this
   forwarding method.




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4.13 Packet Return

   WCCP V2.0 allows a web-cache to decline a redirected packet and return
   it to a router for normal forwarding as specified by the packet's
   destination IP address. The method by which packets are returned from
   router to cache is a matter for negotiation (see Negotiating the
   Packet Return Method).

   When a router receives a returned packet it must not attempt to
   redirect that packet back to a web-cache. Two methods are available to
   prevent any further redirection:

   * Interface Configuration
   * Encapsulation

   The interface configuration method requires that a router is
   configured to inhibit redirection of packets arriving over interfaces
   connected to web-caches. Redirection may be disabled for all packets
   arriving on an interface or for packets where the source MAC
   address is that of a web-cache. This mechanism is efficient but is
   topology dependant and thus may not always be suitable. In this case
   the packet return method in use is L2.

   The encapsulation method requires a web-cache to send returned packets
   to a router with encapsulation. Returned packets are encapsulated in a
   GRE packet [1] with a Protocol Type of 0x883E and contain the original
   Redirect Header or a null Redirect Header if none was present in the
   original redirected packet. The receiving router removes the GRE
   encapsulation from the packets and forwards them without attempting to
   redirect. The packet return method used in this case is GRE.

4.14 Querying Cache Time-Out

   If a router does not receive a WCCP2_HERE_I_AM message from a Service
   Group member for 2.5 * HERE_I_AM_T seconds it will query the member by
   unicasting a WCCP2_REMOVAL_QUERY message to it.  The target Service
   Group member should respond by sending a series of 3 identical
   WCCP2_HERE_I_AM messages, each separated by HERE_I_AM_T/10 seconds.

   If a router does not receive a WCCP2_HERE_I_AM message from a Service
   Group member for 3 * HERE_I_AM_T seconds it will consider the member
   to be unusable and remove it from the Service Group. The web-cache
   will no longer appear in the Router View Info component of the
   WCCP2_I_SEE_YOU message.

   The web-cache will be purged from the assignment data for the Service
   Group.




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4.15 Command and Status Information

   WCCP V2.0 includes a mechanism to allow web-caches to send commands to
   routers within a service group. The same mechanism can be used by the
   routers to provide status information to web-caches.

   The mechanism is implemented by the Command Extension component. This
   component is included in the WCCP2_HERE_I_AM message from a web-cache
   passing commands to routers in a Service Group.

   If a router needs to send status information to a web-cache it will
   include a command in the Command Extension component within its own
   WCCP2_I_SEE_YOU message. That command will indicate the type of status
   information being carried.

5. Protocol Messages

   Each WCCP protocol message is carried in a UDP packet with a
   destination port of 2048. There are four WCCP V2.0 messages:

   * Here I AM
   * I See You
   * Redirect Assign
   * Removal Query

5.1 'Here I Am' Message

   +--------------------------------------+
   |         WCCP Message Header          |
   +--------------------------------------+
   |       Security Info Component        |
   +--------------------------------------+
   |        Service Info Component        |
   +--------------------------------------+
   |  Web-Cache Identity Info Component   |
   +--------------------------------------+
   |    Web-Cache View Info Component     |
   +--------------------------------------+
   | Capability Info Component (optional) |
   +--------------------------------------+
   |Command Extension Component (optional)|
   +--------------------------------------+









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5.2 'I See You' Message

   +--------------------------------------+
   |         WCCP Message Header          |
   +--------------------------------------+
   |       Security Info Component        |
   +--------------------------------------+
   |        Service Info Component        |
   +--------------------------------------+
   |    Router Identity Info Component    |
   +--------------------------------------+
   |      Router View Info Component      |
   +--------------------------------------+
   |       Assignment Info Component      |
   |                OR                    |
   |        Assignment Map Component      |
   +--------------------------------------+
   | Capability Info Component (optional) |
   +--------------------------------------+
   |Command Extension Component (optional)|
   +--------------------------------------+

5.3 'Redirect Assign' Message

   +--------------------------------------+
   |         WCCP Message Header          |
   +--------------------------------------+
   |       Security Info Component        |
   +--------------------------------------+
   |        Service Info Component        |
   +--------------------------------------+
   |      Assignment Info Component       |
   |                OR                    |
   |    Alternate Assignment Component    |
   +--------------------------------------+

5.4 'Removal Query' Message

   +--------------------------------------+
   |         WCCP Message Header          |
   +--------------------------------------+
   |      Security Info Component         |
   +--------------------------------------+
   |       Service Info Component         |
   +--------------------------------------+
   |     Router Query Info Component      |
   +--------------------------------------+




                                                              [Page 15]


5.5 WCCP Message Header

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Type                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Version             |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_HERE_I_AM (10)
      WCCP2_I_SEE_YOU (11)
      WCCP2_REDIRECT_ASSIGN (12)
      WCCP2_REMOVAL_QUERY (13)

   Version

      0x200

   Length

      Length of the WCCP message not including the WCCP Message Header.


5.6 Message Components

   Each WCCP message comprises a WCCP Message Header followed by a number of
   message components. The defined components are:

   * Security Info
   * Service Info
   * Router Identity Info
   * Web-Cache Identify Info
   * Router View Info
   * Web-Cache View Info
   * Assignment Info
   * Router Query Info
   * Capabilities Info
   * Alternate Assignment
   * Assignment Map
   * Command Extension

   Components are padded to align on a four-octet boundary. Each
   component has a 4-octet header specifying the component type and
   length. Note that the length value does not include the 4-octet
   component header.



                                                              [Page 16]


5.6.1 Security Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Security Option                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Security Implementation                   |
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_SECURITY_INFO (0)

   Length

      Length of the remainder of the component.

   Security Option

      WCCP2_NO_SECURITY (0)
      WCCP2_MD5_SECURITY (1)

   Security Implementation

      If Security Option has the value WCCP2_NO_SECURITY then this field is
      not present. If Security Option has the value WCCP2_MD5_SECURITY this
      is a 16-octet field containing the MD5 checksum of the WCCP message and
      the Service Group password. The maximum password length is 8 octets.

      Prior to calculating the MD5 checksum the password should be padded
      out to 8 octets with trailing zeros and the Security Implementation
      field of the Security Option set to zero. The MD5 checksum is calculated
      using the 8 octet padded password and the WCCP message (including the
      WCCP Message Header).











                                                              [Page 17]


5.6.2 Service Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Service Type  |  Service ID   |  Priority     |  Protocol     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Service Flags                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Port 0              |         Port 1                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Port 6              |         Port 7                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_SERVICE_INFO (1)

   Length

      Length of the remainder of the component.

   Service Type

      WCCP2_SERVICE_STANDARD (0).
      Service is a well known service and is described by the Service ID.
      All fields other than Service ID must be zero.

      WCCP2_SERVICE_DYNAMIC (1).
      Service is defined by the Protocol, Service Flags and Port fields.

   Service ID

      Service number. A number in the range 0-255. For well known services
      numbers in the range 0-50 are reserved. The numbers currently defined
      for well known services are:

      0x00    HTTP







                                                              [Page 18]


Priority

      Service priority. The lowest priority is 0, the highest is
      255. Packets for redirection are matched against Services in priority
      order, highest first. Well known services have a priority of 240.

   Protocol

      IP protocol identifier

   Service Flags

      0x0001  Source IP Hash
      0x0002  Destination IP Hash
      0x0004  Source Port Hash
      0x0008  Destination Port Hash
      0x0010  Ports Defined.
      0x0020  Ports Source.
      0x0100  Source IP Alternative Hash
      0x0200  Destination IP Alternative Hash
      0x0400  Source Port Alternative Hash
      0x0800  Destination Port Alternative Hash

      The primary hash flags (Source IP Hash, Destination IP Hash, Source
      Port Hash, Destination Port Hash) determine the key which will be
      hashed to yield the Redirection Hash Table primary bucket index. If
      only the Destination IP Hash flag is set then the packet destination
      IP address is used as the key. Otherwise if any of the primary hash
      flags are set then the key is constructed by XORing the appropriate
      fields from the packet with the key (which has an initial value of
      zero).

      The key is hashed using the following algorithm:

          ulong hash = key;
          hash ^= hash >> 16;
          hash ^= hash >> 8;
          return(hash & 0xFF);

      If alternative hashing has been enabled for the primary bucket (see
      Assignment Info Component) the alternate hash flags (Source IP
      Alternative Hash, Destination IP Alternative Hash, Source Port
      Alternative Hash, Destination Port Alternative Hash) determine the
      key which will be hashed to yield a secondary bucket index. The key
      is constructed by XORing the appropriate fields from the packet with
      a key (which has an initial value of zero).





                                                              [Page 19]


Port 0-7

      Zero terminated list of UDP or TCP port identifiers. Packets will be
      matched against this set of ports if the Ports Defined flag is set. If
      the Ports Source flag is set the port information refers to a source
      port, if clear the port information refers to a destination port.













































                                                              [Page 20]


5.6.3 Router Identity Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Type            |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Router ID Element                       |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sent To Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number Received From                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Received From Address 0                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Received From Address n                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_ROUTER_ID_INFO (2)

   Length

      Length of the remainder of the component.

   Router ID Element

      Element containing the router's identifying IP address and Receive
      ID. The IP address must be a valid, reachable address for the router.

   Sent To Address

      IP address to which the target web-cache sent the WCCP2_HERE_I_AM
      message. When this component is present in a unicast WCCP2_I_SEE_YOU
      message it will contain the IP address that the target web-cache
      used. When present in a multicast WCCP2_I_SEE_YOU message it will
      contain the Service Group multicast address.

   Number Received From

      The number of web-caches to which this message is directed. When using
      multicast addressing it may be less than the number of caches which



                                                              [Page 21]


actually see the message.

   Received From Address 0-n

      List of the IP addresses of web-caches to which this message is
      directed. When using multicast addressing it may be a subset of the
      caches which actually see the message.












































                                                              [Page 22]


5.6.4 Web-Cache Identity Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Web-Cache Identity Element                   |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_WC_ID_INFO (3)

   Length

      Length of the remainder of the component.

   Web-Cache Identity Element

      Element containing the web-cache IP address and Redirection Hash Table
      mapping.




























                                                              [Page 23]


5.6.5 Router View Info Component

   This represents a router's view of the Service Group.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |         Length                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Member Change Number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Assignment Key                         |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Number of Routers                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Router 0                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Router n                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Number of Web-Caches                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Web-Cache Identity Element 0               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Web-Cache Identity Element n               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_RTR_VIEW_INFO (4)

   Length

      Length of the remainder of the component.

   Member Change Number

      Incremented each time there is a change in Service Group membership.



                                                              [Page 24]


Assignment Key

      Assignment Key element received in the last WCCP2_REDIRECT_ASSIGNMENT
      message. Used by the designated web-cache to verify that an assignment
      has been executed.

   Number of Routers

      Number of routers in the Service Group

   Router 0-n

      IP addresses of routers in the Service Group. This list is constructed
      from routers reported by web-caches via WCCP2_HERE_I_AM messages. Note
      that a router does not include itself in the list unless it has also
      been reported via a WCCP2_HERE_I_AM message.

   Number of Web-Caches

      Number of useable web-caches in the Service Group

   Web-Cache Identity Element 0-n

      Identity elements of useable web-caches in Service Group. This list
      contains web-caches that have sent the router a WCCP2_HERE_I_AM
      message with a valid "Received ID".

























                                                              [Page 25]


5.6.6 Web Cache View Info Component

   This represents a web-cache's view of the Service Group.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type                |      Length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Change Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Number of Routers                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router ID Element 0                    |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router ID Element n                    |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Number of Web-Caches                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Web Cache address 0                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Web Cache address n                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_WC_VIEW_INFO (5)

   Length

      Length of the remainder of the component.

   Change Number

      Incremented each time there is a change in the view.

   Number of Routers

      Number of routers in the Service Group




                                                              [Page 26]


Router ID Element 0-n

      List of elements containing the identifying IP address for each router
      in the Service Group and the last "Received ID" from each.

   Number of Web-Caches

      Number of web-caches in the Service Group

   Web Cache address 0-n

      List of web-cache IP addresses learnt from WCCP2_I_SEE_YOU messages.







































                                                              [Page 27]


5.6.7 Assignment Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Assignment Key                        |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Number of Routers                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Router Assignment Element 0                |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              .                                |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Router Assignment Element n                |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Number of Web-Caches                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Web-Cache 0                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              .                                |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Web-Cache n                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Bucket 0   |  Bucket 1     |   Bucket 2    |   Bucket 3    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Bucket 252 |  Bucket 253   |   Bucket 254  |   Bucket 255  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_REDIRECT_ASSIGNMENT (6)

   Length

      Length of the remainder of the component.






                                                              [Page 28]


Assignment Key

      The designated web-cache expects this element to be returned by a router
      in subsequent WCCP2_I_SEE_YOU messages.

   Number of Routers

      Number of routers reachable by the designated web-cache.

   Router Assignment Element 0-n

      Elements containing the router IP address, "Receive ID" and "Change
      Number" for each router.

   Number of Web-Caches

      Number of useable web-caches in the Service Group seen by all routers.

   Web Cache 0-n

      List of the IP addresses of useable web-caches in Service Group. The
      position of a web-cache identifier in this list is the web-cache
      index. The first entry in the list has an index of zero.

   Bucket 0-255

      Contents of the Redirection Hash Table. The content of each bucket is a
      web-cache index value in the range 0-31. If set the A flag indicates
      that alternative hashing should be used for this web-cache. The value
      0xFF indicates no web-cache has been assigned to the bucket.

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      | Index       |A|
      +-+-+-+-+-+-+-+-+
















                                                              [Page 29]


5.6.8 Router Query Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Router ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Receive ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Sent To IP Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Target IP Address                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_QUERY_INFO (7)

   Length

      Length of the remainder of the component.

   Router ID

      Router IP address. The same address advertised in a WCCP2_I_SEE_YOU
      message.

   Receive ID

      Receive ID expected by the router.

   Sent To IP Address

      IP address to which the web-cache sent its last WCCP2_HERE_I_AM
      message. This will not be the Router ID if the web-cache is
      multicasting its WCCP2_HERE_I_AM messages.

   Target IP Address

      IP address of web-cache being queried.









                                                              [Page 30]


5.6.9 Capabilities Info Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Capability Element 0                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Capability Element n                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_CAPABILITY_INFO (8)

   Length

      Length of the remainder of the component.

   Capability Element

      Element in Type-Length-Value format (TLV) describing a router or
      web-cache capability.
























                                                              [Page 31]


5.6.10 Alternate Assignment Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Assignment Type         |     Assignment Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Assignment Body                         |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_ALT_ASSIGNMENT (13)

   Length

      Length of the remainder of the component.

   Assignment Type

      Currently defined values:

      WCCP2_HASH_ASSIGNMENT           (0x00)
      WCCP2_MASK_ASSIGNMENT           (0x01)

   Assignment Length

      Length of Assignment Body

   Assignment Body

      The format of Assignment Body depends upon the value of Assignment Type.

      Assignment Type = WCCP2_HASH_ASSIGNMENT

      In this case the body of the message is identical to the Assignment
      Info Component with the Type and Length fields omitted.










                                                              [Page 32]


Assignment Type = WCCP2_MASK_ASSIGNMENT

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Assignment Key                        |
      |                               .                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Number of Routers                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Router Assignment Element 0                |
      |                              .                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              .                                |
      |                              .                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Router Assignment Element n                |
      |                              .                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Number of Mask/Value Set Elements (m)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Mask/Value Set Element 0                   |
      |                              .                                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               .                               |
      |                               .                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   Mask/Value Set Element m                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Assignment Key

         The designated web-cache expects this element to be returned by a
         router in subsequent WCCP2_I_SEE_YOU messages.

      Number of Routers

         Number of routers reachable by the designated web-cache.

      Router Assignment Element 0-n

         Element containing the router IP address, Receive ID and Change
         Number for each router.

      Number of Mask/Value Set Elements (m)

         Number of Mask/Value Set elements in this message




                                                              [Page 33]


Mask/Value Set Element 0-m

         A list of the Mask/Value Element Sets for the Service Group
















































                                                              [Page 34]


5.6.11 Assignment Map Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type                |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Number of Mask/Value Set Elements (n)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Mask/Value Set Element 0                   |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Mask/Value Set Element n                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_ASSIGN_MAP (14)

   Length

      Length of the remainder of the component.

   Number of Mask/Value Set Elements (n)

      Number of Mask/Value Set elements in the message

   Mask/Value Set Element 0-n

      A list of the Mask/Value Element Sets for the Service Group


















                                                              [Page 35]


5.6.12 Command Extension Component

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Type                |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Command Type            |      Command Length           !
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Command Data                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      WCCP2_COMMAND_EXTENSION (15)

   Length

      Length of the remainder of the component.

   Command Type

      The command specifier.

   Command Length

      The length of the Command Data field of this command

   The defined Command Types are:

   Command Type:   WCCP2_COMMAND_TYPE_SHUTDOWN (01)
   Command Length: 4
   Command Data:   Web-cache IP address
   Description:    This command is used by a web-cache to indicate to
                   the routers in a Service Group that it is shutting
                   down and should no longer receive any redirected traffic.


   Command Type:   WCCP2_COMMAND_TYPE_SHUTDOWN_RESPONSE (02)
   Command Length: 4
   Command Data:   Web-cache IP address.
   Description:    This command is used by a router to acknowledge
                   receipt of a SHUTDOWN command received from the web-cache
                   identified by the IP address in the Command Data field.




                                                              [Page 36]


5.7 Information Elements

5.7.1 Router ID Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Router ID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Receive ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Router ID

      Router's identifying IP address. This must be a valid IP address by
      which the router is reachable.

   Receive ID

      Defined per Service Group. Incremented each time the router sends a WCCP
      protocol message including a Router Identity Info component. Will never be
      zero.

5.7.2 Web-Cache Identity Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         WC Address                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Hash Revision          |U|        Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Bucket Block 0                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Bucket Block 7                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Assignment Weight          |           Status              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   WC Address

      Web-Cache IP address





                                                              [Page 37]


Hash Revision

      0x00

   U

      If set indicates that the web cache does not have an assignment in the
      Redirection Hash Table and that Bucket Block data is historical.
      Historical data may be used by the designated web-cache to re-assign
      the same bucket set to a web-cache that left and subsequently
      rejoined a Service Group.

   Bucket Block 0-7

      256-bit vector. A set bit indicates the corresponding Redirection
      Hash Table bucket is assigned to this web-cache.

   Assignment Weight

      Hash weight. May be used to indicate to the designated web-cache how new
      assignments should be made.

   Status

      Hash status. May be used to indicate to the designated web-cache how new
      assignments should be made.

5.7.3 Assignment Key Element

   This element identifies a particular assignment.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Key IP Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Key Change Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Key IP Address

      Designated web-cache IP address

   Key Change Number

      Incremented if a change has occurred.





                                                              [Page 38]


5.7.4 Router Assignment Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Router ID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Receive ID                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Change Number                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Router ID

      Router's identifying IP address. It must be a valid address by which
      the router is reachable.

   Receive ID

      Last Receive ID received from the router identified by Router
      ID. A router will ignore an assignment if Receive ID is invalid.

   Change Number

      Last Member Change Number received from the router identified by
      Router ID. A router will ignore an assignment if Change Number is
      invalid.

5.7.5 Capability Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Type              |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Value                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type

      Currently defined types are:

      WCCP2_FORWARDING_METHOD     0x01
      WCCP2_ASSIGNMENT_METHOD     0x02
      WCCP2_PACKET_RETURN_METHOD  0x03






                                                              [Page 39]


Length

      Length of Capability element Value

   Value

      The length and format of the value field is dependant on the capability type.

      Type = WCCP2_FORWARDING_METHOD

      A 32-bit bitmask indicating supported/selected forwarding methods.
      Currently defined values are:

      WCCP2_FORWARDING_METHOD_GRE     0x00000001
      WCCP2_FORWARDING_METHOD_L2      0x00000002

      Type = WCCP2_ASSIGNMENT_METHOD

      A 32-bit bitmask indicating supported/selected assignment methods.
      Currently defined values are:

      WCCP2_ASSIGNMENT_METHOD_HASH    0x00000001
      WCCP2_ASSIGNEMNT_METHOD_MASK    0x00000002

      Type = WCCP2_PACKET_RETURN_METHOD

      A 32-bit bitmask indicating supported/selected packet return methods.
      Currently defined values are:

      WCCP2_PACKET_RETURN_METHOD_GRE  0x00000001
      WCCP2_PACKET_RETURN_METHOD_L2   0x00000002

5.7.6 Mask/Value Set Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Mask Element                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Number of Value Elements (n)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Value Element 0                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              .                                |
   |                              .                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Value Element n                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



                                                              [Page 40]


Mask Element

      Mask element for this set.

   Number of Value Elements (n)

      The number of value elements in this set.

   Value Element 0-n

      The list of value elements for this set.

5.7.7 Mask Element

   Note that in all of the mask fields of this element a zero means
   "Don't care".

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Address Mask                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Destination Address Mask                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Source Port Mask         |   Destination Port Mask       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Source Address Mask

      The 32 bit mask to be applied to the source IP address of the packet.

   Destination Address Mask

      The 32 bit mask to be applied to the destination IP address of the packet.

   Source Port Mask

      The 16 bit mask to be applied to the TCP/UDP source port field of the packet.

   Destination Port Mask

      The 16 bit mask to be applied to the TCP/UDP destination port field of the packet.









                                                              [Page 41]


5.7.8 Value Element

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Source Address Value                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Address Value                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Source Port Value        |   Destination Port Value      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Web Cache IP Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Source Address Value

      The value to match against the source IP address of the packet after
      masking.

   Destination Address Value

      The value to match against the destination IP address of the packet after
      masking.

   Source Port Value

      The value to match against the TCP/UDP source port number of the
      packet after masking.

   Destination Port Value

      The value to match against the TCP/UDP destination port number of the
      packet after masking.

   Web-cache IP address

      The IP address of the web-cache to which packets matching this value
      element should be sent.













                                                              [Page 42]


6. Security Considerations

   WCCP V2 provides a mechanism for message authentication. It is
   described in section 4.7 of this document. The authentication
   mechanism relies on a password known to all routers and web-caches in
   a Service Group. The password is part of the Service Group
   configuration and is used to compute message checksums which can be
   verified by other members of the group. Should the password become
   known to a host attempting to disrupt the operation of a Service Group
   it would be possible for that host to spoof WCCP messages and appear
   as either a router or web-cache in the Service Group.

   To pose as a router in a Service Group a host would advertise its
   presence to the members of the group in I_SEE_YOU messages.  If
   accepted as part of the Service Group the host would receive the
   configuration for the group in a HERE_I_AM message from the designated
   web-cache. This situation would not pose any threat to the operation
   of the Service Group because the host would not be performing any
   packet redirection and all packets would flow normally.

   To pose as a web-cache within a Service Group a host would advertise
   its presence in HERE_I_AM messages. Acceptance of the host as part of
   the Service Group would be decided by the designated cache and may be
   subject to additional security checks not specified by WCCP. Should
   the host become part of the Service Group it would be assigned a
   proportion of the traffic redirected by the routers in the Service
   Group. Assuming that the host drops any redirected packets the net
   effect to clients would be that some attempts to retrieve content via
   the Service Group routers would fail.


7. References

   [1] Hanks, Li, Farinacci & Traina, "Generic Routing Encapsulation
   (GRE)", RFC 1701, October 1994


8. Authors' Addresses

   Martin Cieslak
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143

   David Forster
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143



                                                              [Page 43]


Gurumukh Tiwana
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143

   Rob Wilson
   Cisco Systems
   170 Tasman Drive
   San Jose, CA 95143

   email: robewils@cisco.com

   Expires January 2001






































                                                              [Page 44]


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