draft-ietf-ipv6-ndproxy-00.txt   draft-ietf-ipv6-ndproxy-01.txt 
IPv6 Working Group D. Thaler IPv6 Working Group D. Thaler
INTERNET-DRAFT M. Talwar INTERNET-DRAFT M. Talwar
November 29, 2004 Microsoft February 15, 2005 Microsoft
Expires May 2005 C. Patel Expires August 2005 C. Patel
All Play, No Work All Play, No Work
Bridge-like Neighbor Discovery Proxies (ND Proxy) Bridge-like Neighbor Discovery Proxies (ND Proxy)
<draft-ietf-ipv6-ndproxy-00.txt> <draft-ietf-ipv6-ndproxy-01.txt>
Status of this Memo Status of this Memo
By submitting this Internet-Draft, I certify that any applicable By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been patent or other IPR claims of which I am aware have been
disclosed, or will be disclosed, and any of which I become aware disclosed, or will be disclosed, and any of which I become aware
will be disclosed, in accordance with RFC 3668. will be disclosed, in accordance with RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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progress." progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Copyright Notice Copyright Notice
Draft ND Proxy November 2004 Draft ND Proxy February 2005
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract Abstract
Bridging multiple links into a single entity has several Bridging multiple links into a single entity has several
operational advantages. A single subnet prefix is sufficient to operational advantages. A single subnet prefix is sufficient to
support multiple physical links. There is no need to allocate support multiple physical links. There is no need to allocate
subnet numbers to the different networks, simplifying management. subnet numbers to the different networks, simplifying management.
Bridging some types of media requires network-layer support, Bridging some types of media requires network-layer support,
however. This document describes these cases and specifies the however. This document describes these cases and specifies the
IP-layer support that enables bridging under these circumstances. IP-layer support that enables bridging under these circumstances.
The behavior of one common type of IPv4 ARP Proxy deployed today
is documented herein for informational purposes, but this document
concentrates on describing similar behavior for IPv6.
1. Introduction 1. Introduction
In the IPv4 Internet today, it is common for Network Address In the IPv4 Internet today, it is common for Network Address
Translators (NATs) [NAT] to be used to easily connect one or more Translators (NATs) [NAT] to be used to easily connect one or more
leaf links to an existing network without requiring any leaf links to an existing network without requiring any
coordination with the network service provider. Since NATs modify coordination with the network service provider. Since NATs modify
IP addresses in packets, they are problematic for many IP IP addresses in packets, they are problematic for many IP
applications. As a result, it is desirable to address the problem applications. As a result, it is desirable to address the problem
(for both IPv4 and IPv6) without the need for NATs. (for both IPv4 and IPv6) without the need for NATs.
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o It requires all ports to support the same type of link-layer o It requires all ports to support the same type of link-layer
addressing (in particular, IEEE 802 addressing). addressing (in particular, IEEE 802 addressing).
As a result, two common scenarios, described below, are not As a result, two common scenarios, described below, are not
solved, and it is these two scenarios we specifically target in solved, and it is these two scenarios we specifically target in
this document. While the mechanism described herein may apply to this document. While the mechanism described herein may apply to
other scenarios as well, we will concentrate our discussion on other scenarios as well, we will concentrate our discussion on
these two scenarios. these two scenarios.
Draft ND Proxy November 2004 Draft ND Proxy February 2005
1.1. SCENARIO 1: Wireless upstream 1.1. SCENARIO 1: Wireless upstream
The following figure illustrates a likely example: The following figure illustrates a likely example:
| +-------+ +--------+ | +-------+ +--------+
local |Ethernet | | Wireless | Access | local |Ethernet | | Wireless | Access |
+---------+ A +-))) (((-+ +--> rest of network +---------+ A +-))) (((-+ +--> rest of network
hosts | | | link | Point | hosts | | | link | Point |
| +-------+ +--------+ | +-------+ +--------+
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local subnet. Secondly, the extent to which Prefix Delegation is local subnet. Secondly, the extent to which Prefix Delegation is
supported, and supported without additional charge, is up to the supported, and supported without additional charge, is up to the
service provider. Hence, there is no guarantee that Prefix service provider. Hence, there is no guarantee that Prefix
Delegation will work without explicit configuration or additional Delegation will work without explicit configuration or additional
charge. Bridging, on the other hand, allows the device to work charge. Bridging, on the other hand, allows the device to work
with zero configuration, regardless of the service provider's with zero configuration, regardless of the service provider's
policies, just as a NAT does. Hence bridging avoids the incentive policies, just as a NAT does. Hence bridging avoids the incentive
to NAT IPv6 just to avoid paying for, or requiring configuration to NAT IPv6 just to avoid paying for, or requiring configuration
to get, another prefix. to get, another prefix.
Draft ND Proxy November 2004 Draft ND Proxy February 2005
1.2. SCENARIO 2: PPP upstream 1.2. SCENARIO 2: PPP upstream
The following figure illustrates another likely example: The following figure illustrates another likely example:
| +-------+ +--------+ | +-------+ +--------+
local |Ethernet | | PPP link | | local |Ethernet | | PPP link | |
+---------+ A +-----------+ Router +--> rest of network +---------+ A +-----------+ Router +--> rest of network
hosts | | | | | hosts | | | | |
| +-------+ +--------+ | +-------+ +--------+
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In this document we make no distinction between a "link" (in the In this document we make no distinction between a "link" (in the
classic IPv6 sense) and a "subnet". We use the term "segment" to classic IPv6 sense) and a "subnet". We use the term "segment" to
apply to a bridged component of the link. apply to a bridged component of the link.
Finally, while it is possible that functionality equivalent to Finally, while it is possible that functionality equivalent to
that described herein may be achieved by nodes which do not that described herein may be achieved by nodes which do not
fulfill all the requirements in [NODEREQ], in the remainder of fulfill all the requirements in [NODEREQ], in the remainder of
this document we will describe behavior in terms of an IPv6 node this document we will describe behavior in terms of an IPv6 node
as defined in that document. as defined in that document.
Draft ND Proxy November 2004 Draft ND Proxy February 2005
3. Requirements 3. Requirements
Bridge-like proxy behavior is designed with the following Bridge-like proxy behavior is designed with the following
requirements in mind: requirements in mind:
o Support connecting multiple segments with a single subnet o Support connecting multiple segments with a single subnet
prefix. prefix.
o Support media which cannot be bridged at the link-layer. o Support media which cannot be bridged at the link-layer.
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being bridged. being bridged.
o Provide full connectivity between all nodes in the subnet. o Provide full connectivity between all nodes in the subnet.
For example, if there are existing nodes (such as any routers For example, if there are existing nodes (such as any routers
on the subnet) which have addresses in the subnet prefix, on the subnet) which have addresses in the subnet prefix,
adding a bridge-like proxy must allow bridged nodes to have adding a bridge-like proxy must allow bridged nodes to have
full connectivity with existing nodes on the subnet. full connectivity with existing nodes on the subnet.
o Prevent loops. o Prevent loops.
o Also work in the absense of any routers. o Also work in the absence of any routers.
o Support secure IPv6 neighbor discovery. This is discussed in
the Security Considerations section.
o Support nodes moving between segments. For example, a node o Support nodes moving between segments. For example, a node
should be able to keep its address without seeing its address should be able to keep its address without seeing its address
as a duplicate due to any cache maintained at the proxy. as a duplicate due to any cache maintained at the proxy.
o Allow dynamic addition/removal of a proxy without adversely o Allow dynamic addition of a proxy without adversely
disrupting the network. disrupting the network.
o The proxy behavior should not break any existing classic o The proxy behavior should not break any existing classic
bridges in use on a network segment. bridges in use on a network segment.
Draft ND Proxy November 2004
3.1. Non-requirements 3.1. Non-requirements
The following items are not considered requirements, as they are The following items are not considered requirements, as they are
not met by classic bridges: not met by classic bridges:
Draft ND Proxy February 2005
o Show up as a hop in a traceroute. o Show up as a hop in a traceroute.
o Use the shortest path between two nodes on different o Use the shortest path between two nodes on different
segments. segments.
o Be able to use all available interfaces simultaneously. o Be able to use all available interfaces simultaneously.
Instead, bridging technology relies on disabling redundant Instead, bridging technology relies on disabling redundant
interfaces to prevent loops. interfaces to prevent loops.
o Support connecting media on which Neighbor Discovery is not o Support connecting media on which Neighbor Discovery is not
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While this scenario may be desirable, no solution is While this scenario may be desirable, no solution is
currently known which does not have undesirable side effects currently known which does not have undesirable side effects
outside the subnet. As a result, this scenario is outside outside the subnet. As a result, this scenario is outside
the scope of this document. the scope of this document.
4. Bridge-Like Proxy Behavior 4. Bridge-Like Proxy Behavior
Network layer support for proxying between multiple interfaces Network layer support for proxying between multiple interfaces
SHOULD be used only when classic bridging is not possible. SHOULD be used only when classic bridging is not possible.
Draft ND Proxy November 2004
When a proxy interface comes up, the node puts it in "all- When a proxy interface comes up, the node puts it in "all-
multicast" mode so that it will receive all multicast packets. It multicast" mode so that it will receive all multicast packets. It
is common for interfaces to not support full promiscuous mode is common for interfaces to not support full promiscuous mode
(e.g., on a wireless client), but all-multicast mode is generally (e.g., on a wireless client), but all-multicast mode is generally
still supported. still supported.
Draft ND Proxy February 2005
As with all other interfaces, IPv4 and IPv6 maintain a neighbor As with all other interfaces, IPv4 and IPv6 maintain a neighbor
cache (aka "ARP cache") for each proxy interface, which will be cache (aka "ARP cache") for each proxy interface, which will be
used as described below. For readability, we will describe the used as described below. For readability, we will describe the
neighbor cache as if both IPv4 and IPv6 neighbors use the same neighbor cache as if both IPv4 and IPv6 neighbors use the same
state machine described in [ND]. state machine described in [ND].
4.1. Receiving Packets 4.1. Forwarding Packets
When a packet from any IP source address other than the When a packet from any IP source address other than the
unspecified address is received on a proxy interface, the neighbor unspecified address is received on a proxy interface, the neighbor
cache of that interface SHOULD be consulted to find an entry for cache of that interface SHOULD be consulted to find an entry for
the source IP address. If no entry exists, one is created in the the source IP address. If no entry exists, one is created in the
STALE state. STALE state.
When any IP or ARP packet is received on a proxy interface, it When any IP or ARP packet is received on a proxy interface, it
must be parsed to see whether it is known to be of a type that must be parsed to see whether it is known to be of a type that
negotiates link-layer addresses. This document covers the negotiates link-layer addresses. This document covers the
following types: ARP, IPv6 Neighbor Discovery, IPv6 Router following types: ARP, IPv6 Neighbor Discovery, IPv6 Router
Discovery, IPv6 Redirects, and DHCPv4. These packets are ones Discovery, IPv6 Redirects, and DHCPv4. These packets are ones
that can carry link-layer addresses, and hence must be proxied (as that can carry link-layer addresses, and hence must be proxied (as
described below) so that packets between nodes on different described below) so that packets between nodes on different
segments can be received by the proxy and have the correct link- segments can be received by the proxy and have the correct link-
layer address type on each segment. layer address type on each segment.
When any other IP broadcast or multicast packet (other than to the When any other IP broadcast or multicast packet (other than to the
IPv6 Link-scoped STP Multicast Group) is received on a proxy IPv6 Link-scoped STP Multicast Group) is received on a proxy
interface, in addition to any normal IP behavior such as being interface, in addition to any normal IP behavior such as being
delivered locally, it is forwarded unchanged out all other proxy delivered locally, it is forwarded unchanged (other than using a
interfaces on the same link. (As specified in [BRIDGE], the proxy new link-layer header) out all other proxy interfaces on the same
may instead support multicast learning and filtering but this is link. (As specified in [BRIDGE], the proxy may instead support
optional.) In particular, the IPv4 TTL or IPv6 Hop Limit is not multicast learning and filtering but this is OPTIONAL.) In
updated, and no ICMP errors are sent as a result of attempting particular, the IPv4 TTL or IPv6 Hop Limit is not updated, and no
this forwarding. ICMP errors (except as noted in Section 4.1.1 below) are sent as a
result of attempting this forwarding.
When any other IP unicast packet is received on a proxy interface, When any other IP unicast packet is received on a proxy interface,
if it is not locally destined then it is forwarded unchanged to if it is not locally destined then it is forwarded unchanged
the proxy interface for which the next hop address appears in the (other than using a new link-layer header) to the proxy interface
neighbor cache. Again the IPv4 TTL or IPv6 Hop Limit is not for which the next hop address appears in the neighbor cache.
Again the IPv4 TTL or IPv6 Hop Limit is not updated, and no ICMP
errors (except as noted in Section 4.1.1 below) are sent as a
result of attempting this forwarding. To choose a proxy interface
to forward to, the neighbor cache is consulted, and the interface
with the neighbor entry in the "best" state is used. In order of
Draft ND Proxy November 2004 Draft ND Proxy February 2005
updated, and no ICMP errors are sent as a result of attempting least to most preferred, the states (per [ND]) are INCOMPLETE,
this forwarding. To choose a proxy interface to forward to, the STALE, DELAY, PROBE, REACHABLE. A packet is never forwarded back
neighbor cache is consulted, and the interface with the neighbor out the same interface on which it arrived; such a packet is
entry in the "best" state is used. In order of least to most instead silently dropped.
preferred, the states (per [ND]) are INCOMPLETE, STALE, DELAY,
PROBE, REACHABLE. A packet is never forwarded back out the same
interface on which it arrived; such a packet is instead silently
dropped.
If no cache entry exists (as may happen if the proxy has If no cache entry exists (as may happen if the proxy has
previously evicted the cache entry or if the proxy is restarted), previously evicted the cache entry or if the proxy is restarted),
the proxy SHOULD queue the packet and initiate Neighbor Discovery the proxy SHOULD queue the packet and initiate Neighbor Discovery
as if the packet were being locally generated. The proxy MAY as if the packet were being locally generated. The proxy MAY
instead silently drop the packet. In this case, the entry will instead silently drop the packet. In this case, the entry will
eventually be recreated when the sender re-attempts neighbor eventually be recreated when the sender re-attempts neighbor
discovery. discovery.
The link layer header, and the link-layer address within the The link layer header, and the link-layer address within the
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interface. interface.
2) The destination address will be the address in the neighbor 2) The destination address will be the address in the neighbor
entry corresponding to the destination IP address. entry corresponding to the destination IP address.
3) The link-layer address within the payload is substituted with 3) The link-layer address within the payload is substituted with
the address of the outgoing interface. the address of the outgoing interface.
4.1.1. Sending Packet Too Big Messages 4.1.1. Sending Packet Too Big Messages
Whenever any packet is to be forwarded out an interface whose MTU Whenever any IPv4 packet is to be forwarded out an interface whose
is smaller than the size of the packet, the ND proxy drops the MTU is smaller than the size of the packet, and the Dont Fragment
packet and sends a Packet Too Big message back to the source, as bit is set, the ARP proxy drops the packet and sends a
described in [ICMPv6]. Fragmentation Needed message back to the source.
Similarly, whenever any IPv6 packet is to be forwarded out an
interface whose MTU is smaller than the size of the packet, the ND
proxy drops the packet and sends a Packet Too Big message back to
the source, as described in [ICMPv6].
4.1.2. Proxying Packets With Link-Layer Addresses 4.1.2. Proxying Packets With Link-Layer Addresses
Once it is determined that the packet is either Once it is determined that the packet is either
multicast/broadcast or else is not locally destined (if unicast), multicast/broadcast or else is not locally destined (if unicast),
the special types enumerated above (ARP, etc.) that carry link- the special types enumerated above (ARP, etc.) that carry link-
layer addresses are handled by generating a proxy packet that layer addresses are handled by generating a proxy packet that
contains the proxy's link-layer address on the outgoing interface
Draft ND Proxy November 2004 Draft ND Proxy February 2005
contains the proxy's link-layer address on the outgoing interface
instead. Section 7, "Guidelines to proxy developers", describes instead. Section 7, "Guidelines to proxy developers", describes
the scenarios in which the link-layer address substitution in the the scenarios in which the link-layer address substitution in the
payload should be performed. payload should be performed.
As with all forwarded packets, the link-layer header is also new. As with all forwarded packets, the link-layer header is also new.
Note that any change to the length of a proxied packet, such as Note that any change to the length of a proxied packet, such as
when the link-layer address length changes, will require when the link-layer address length changes, will require
corresponding changes to fields in the IP header, namely the IPv4 corresponding changes to fields in the IP header, namely the IPv4
Total Length and Header Checksum fields, or the IPv6 Payload Total Length and Header Checksum fields, or the IPv6 Payload
Length field. Length field.
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locally destined, and then the ARP REPLY is proxied as described locally destined, and then the ARP REPLY is proxied as described
above. above.
4.1.3.3. DHCPv4 Packets 4.1.3.3. DHCPv4 Packets
If the received packet is a DHCPv4 DISCOVER or REQUEST message, If the received packet is a DHCPv4 DISCOVER or REQUEST message,
then instead of changing the client's hardware address in the then instead of changing the client's hardware address in the
payload, the BROADCAST (B) flag is set in the proxied packet. payload, the BROADCAST (B) flag is set in the proxied packet.
This ensures that the proxy will be able to receive and proxy the This ensures that the proxy will be able to receive and proxy the
response since the response will be broadcast rather than unicast response since the response will be broadcast rather than unicast
to that hardware address. The hardware address is thus used only
Draft ND Proxy November 2004 Draft ND Proxy February 2005
to that hardware address. The hardware address is thus used only
as a unique identifier and hence need not be a link-layer address as a unique identifier and hence need not be a link-layer address
on the same segment. on the same segment.
One limitation of this rule is that if the authentication protocol
for DHCPv4 described in [DHCPAUTH] is used, only clients that set
the BROADCAST flag themselves will be able to use DHCPv4 through
the proxy. If [DHCPAUTH] is not used, a DHCPv4 client might still
detect, with previously undefined behavior, that the broadcast bit
has been changed from the setting in the message originally set by
the client. However, the point of this rule is not to solve this
problem, but rather to document existing practice.
4.1.4. IPv6 ND Proxying 4.1.4. IPv6 ND Proxying
When any IPv6 packet is received on a proxy interface, it must be When any IPv6 packet is received on a proxy interface, it must be
parsed to see whether it is known to be one of the following parsed to see whether it is known to be one of the following
types: IPv6 Neighbor Discovery, IPv6 Router Discovery, or IPv6 types: IPv6 Neighbor Discovery, IPv6 Router Discovery, or IPv6
Redirects. Redirects.
4.1.4.1. ICMPv6 Neighbor Solicitations 4.1.4.1. ICMPv6 Neighbor Solicitations
If the received packet is an ICMPv6 Neighbor Solicitation, the NS If the received packet is an ICMPv6 Neighbor Solicitation, the NS
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from one segment to another since it never responds to an NS based from one segment to another since it never responds to an NS based
on its own cache. on its own cache.
4.1.4.2. ICMPv6 Neighbor Advertisements 4.1.4.2. ICMPv6 Neighbor Advertisements
If the received packet is an ICMPv6 Neighbor Advertisement, the If the received packet is an ICMPv6 Neighbor Advertisement, the
neighbor cache on the receiving interface is first updated as if neighbor cache on the receiving interface is first updated as if
the NA were locally destined, and then the NA is proxied as the NA were locally destined, and then the NA is proxied as
described above. described above.
4.1.4.3. ICMPv6 Redirects 4.1.4.3. ICMPv6 Router Advertisements
Unless STP is implemented as described in section 6, the following
special processing is done for IPv6 Router Advertisements (RAs).
Draft ND Proxy February 2005
A new "Proxy" bit is defined in the existing Router Advertisement
flags field as follows:
+-+-+-+-+-+-+-+-+
|M|O|H|Prf|P|Rsv|
+-+-+-+-+-+-+-+-+
where "P" indicates the location of the Proxy bit, and "Rsv
indicates the remaining reserved bits.
The proxy determines an "upstream" proxy interface, typically
through a physical choice dictated by the scenario (see Scenarios
1 and 2 above), or through manual configuration.
When an RA with the P bit clear arrives on the upstream interface,
the P bit is set when the RA is proxied out all other
("downstream") proxy interfaces (see secion 6).
If an RA with the P bit set has arrived on a given interface
(including the upstream interface) within the last 60 minutes,
that interface MUST NOT be used as a proxy interface; i.e., proxy
functionality is disabled on that interface.
Furthermore, if any RA (regardless of the value of the P bit) has
arrived on a "downstream" proxy interface within the last 60
minutes, that interface MUST NOT be used as a proxy interface.
4.1.4.4. ICMPv6 Redirects
If the received packet is an ICMPv6 Redirect message, then the If the received packet is an ICMPv6 Redirect message, then the
proxied packet should be modified as follows. If the proxy has a proxied packet should be modified as follows. If the proxy has a
valid (i.e., not INCOMPLETE) neighbor entry for the target address valid (i.e., not INCOMPLETE) neighbor entry for the target address
on the same interface as the redirected host, then the TLLA option on the same interface as the redirected host, then the TLLA option
in the proxied Redirect simply contains the link-layer address of in the proxied Redirect simply contains the link-layer address of
the target as found in the proxy's neighbor entry, since the the target as found in the proxy's neighbor entry, since the
redirected host may reach the target address directly. Otherwise, redirected host may reach the target address directly. Otherwise,
if the proxy has a valid neighbor entry for the target address on if the proxy has a valid neighbor entry for the target address on
some other interface, then the TLLA option in the proxied packet some other interface, then the TLLA option in the proxied packet
contains the link-layer address of the proxy on the sending contains the link-layer address of the proxy on the sending
interface, since the redirected host must reach the target address interface, since the redirected host must reach the target address
through the proxy. Otherwise, the proxy has no valid neighbor through the proxy. Otherwise, the proxy has no valid neighbor
Draft ND Proxy November 2004
entry for the target address, and the proxied packet contains no entry for the target address, and the proxied packet contains no
TLLA option, which will cause the redirected host to perform TLLA option, which will cause the redirected host to perform
neighbor discovery for the target address. neighbor discovery for the target address.
4.2. Sending Packets Draft ND Proxy February 2005
4.2. Originating Packets
Locally originated packets that are sent on a proxy interface also Locally originated packets that are sent on a proxy interface also
follow the same rules as packets received on a proxy interface. follow the same rules as packets received on a proxy interface.
If no neighbor entry exists when a unicast packet is to be locally If no neighbor entry exists when a unicast packet is to be locally
originated, an interface can be chosen in any implementation- originated, an interface can be chosen in any implementation-
specific fashion. Once the neighbor is resolved, the actual specific fashion. Once the neighbor is resolved, the actual
interface will be discovered and the packet will be sent on that interface will be discovered and the packet will be sent on that
interface. When a multicast or broadcast packet is to be locally interface. When a multicast or broadcast packet is to be locally
originated, an interface can be chosen in any implementation- originated, an interface can be chosen in any implementation-
specific fashion, and the packet will then be forwarded out other specific fashion, and the packet will then be forwarded out other
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is created as well as a neighbor cache entry in the INCOMPLETE is created as well as a neighbor cache entry in the INCOMPLETE
state. Before the packet can be sent, A needs to resolve B's state. Before the packet can be sent, A needs to resolve B's
link-layer address and sends a Neighbor Solicitation (NS) to the link-layer address and sends a Neighbor Solicitation (NS) to the
solicited-node multicast address for B. The SLLA option in the solicited-node multicast address for B. The SLLA option in the
solicitation contains A's link-layer address. solicitation contains A's link-layer address.
P receives the solicitation (since it is receiving all link-layer P receives the solicitation (since it is receiving all link-layer
multicast packets) and processes it as it would any multicast multicast packets) and processes it as it would any multicast
packet by forwarding it out to other segments on the link. packet by forwarding it out to other segments on the link.
However, before actually sending the packet, it determines if the However, before actually sending the packet, it determines if the
Draft ND Proxy November 2004
packet being sent is one which requires proxying. Since it is an packet being sent is one which requires proxying. Since it is an
NS, it creates a neighbor entry for A on interface 1 and records NS, it creates a neighbor entry for A on interface 1 and records
its link-layer address. It also creates a neighbor entry for B its link-layer address. It also creates a neighbor entry for B
(on an arbitrary proxy interface) in the INCOMPLETE state. Since (on an arbitrary proxy interface) in the INCOMPLETE state. Since
the packet is multicast, P then needs to proxy the NS out all the packet is multicast, P then needs to proxy the NS out all
Draft ND Proxy February 2005
other proxy interfaces on the subnet. Before sending the packet other proxy interfaces on the subnet. Before sending the packet
out interface 2, it replaces the link-layer address in the SLLA out interface 2, it replaces the link-layer address in the SLLA
option with its own link-layer address, p2. option with its own link-layer address, p2.
B receives this NS, processing it as usual. Hence it creates a B receives this NS, processing it as usual. Hence it creates a
neighbor entry for A mapping it to the link-layer address p2. It neighbor entry for A mapping it to the link-layer address p2. It
responds with a Neighbor Advertisement (NA) sent to A containing responds with a Neighbor Advertisement (NA) sent to A containing
B's link-layer address b. The NA is sent using A's neighbor B's link-layer address b. The NA is sent using A's neighbor
entry, i.e. to the link-layer address p2. entry, i.e. to the link-layer address p2.
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address b. P then replaces the link-layer address in the TLLA address b. P then replaces the link-layer address in the TLLA
option with its own link-layer address on the outgoing interface, option with its own link-layer address on the outgoing interface,
p1. The packet is then sent out interface 1. p1. The packet is then sent out interface 1.
A receives this NA, processing it as usual. Hence it creates a A receives this NA, processing it as usual. Hence it creates a
neighbor entry for B on interface 2 in the REACHABLE state and neighbor entry for B on interface 2 in the REACHABLE state and
records the link-layer address p1. records the link-layer address p1.
6. Loop Prevention 6. Loop Prevention
Loop prevention can be done done by having the proxy implement the An implementation MUST ensure that loops are prevented, via
Spanning Tree Algorithm and Protocol as defined in [BRIDGE] on all either:
proxy interfaces. Loop prevention is OPTIONAL, and is useful only
if the proxy can be deployed in an environment where physical
loops are possible. For example, in a cell phone which proxies
between a PPP dialup link and a local Ethernet interface, it is
typically safe to assume that physical loops are not possible and
hence there is no need to support the Spanning Tree Protocol
(STP).
If loop prevention is implemented, it is done as follows. IEEE a) by using the P bit in RA's as described below, or
802 interfaces use the protocol exactly as specified in [BRIDGE].
Operation of the Spanning Tree Protocol (STP) over other types of
Draft ND Proxy November 2004 b) by running the Spanning Tree Algorithm and Protocol defined
in [BRIDGE] on all proxy interfaces as described below, or
link layers is done by encapsulating the STP frame in an IPv6 c) by being physically deployable only in an environment where
header as follows. The Next Header field is set to [TBA by IANA], physical loops cannot occur. For example, in a cell phone
indicating that an STP header follows. The Destination Address which proxies between a PPP dialup link and a local Ethernet
field is set to the Link-scoped STP Multicast Group [TBA by IANA]. interface, it is typically safe to assume that physical loops
All proxies operating on non-IEEE 802 media join this group so are not possible and hence there is no need to support the
they will receive STP packets. STP packets are never forwarded or Spanning Tree Protocol (STP).
proxied.
Loop prevention using STP would typically be done by devices that
already implement this protocol as a result of supporting normal
briding functionality, and is done here as follows. IEEE 802
Draft ND Proxy February 2005
interfaces use the protocol exactly as specified in [BRIDGE].
Operation of STP over other types of link layers is done by
encapsulating the STP frame in an IPv6 header. The Next Header
field is set to [TBA by IANA], indicating that an STP header
follows. The Destination Address field is set to the Link-scoped
STP Multicast Group [TBA by IANA]. All proxies operating on non-
IEEE 802 media join this group so they will receive STP packets.
STP packets are never forwarded or proxied.
Loop avoidance using the P bit in RAs is done as follows. The
proxy determines an "upstream" proxy interface, typically through
a physical choice dictated by the scenario (see Scenarios 1 and 2
above), or through manual configuration. As described in Section
4.1.3.3, only the upstream interface is allowed to receive RAs,
and never from other proxies. Proxy functionality is disabled on
an interface otherwise. Finally, a proxy MUST wait until it has
sent two P bit RAs on a given "downstream" interface before it
enables forwarding on that interface.
7. Guidelines to proxy developers 7. Guidelines to proxy developers
Proxy developers will have to accomodate protocols or protocol Proxy developers will have to accomodate protocols or protocol
options (for example, new ICMP messages) that are developed in the options (for example, new ICMP messages) that are developed in the
future, or protocols that are not mentioned in this document (for future, or protocols that are not mentioned in this document (for
example, proprietary protocols). This section prescribes example, proprietary protocols). This section prescribes
guidelines that can be used by proxy developers to accomodate guidelines that can be used by proxy developers to accomodate
protocols that are not mentioned herein. protocols that are not mentioned herein.
skipping to change at page 13, line 39 skipping to change at page 15, line 4
hence, the proxy substitutes it with its own address. hence, the proxy substitutes it with its own address.
For broadcast/multicast packets, the link-layer address For broadcast/multicast packets, the link-layer address
substituted within the payload will be different for each substituted within the payload will be different for each
outgoing interface. outgoing interface.
2) If the link-layer address in the payload of the protocol will 2) If the link-layer address in the payload of the protocol will
never be used in any link-layer header, then the proxy should never be used in any link-layer header, then the proxy should
not substitute it with its own address. No special actions not substitute it with its own address. No special actions
are required for supporting these protocols. For example, are required for supporting these protocols. For example,
Draft ND Proxy February 2005
[DHCPv6] is in this category. [DHCPv6] is in this category.
8. IANA Considerations 8. IANA Considerations
To support loop prevention over non-802 media, IANA should assign: To support loop prevention over non-802 media, IANA should assign:
1) a Protocol Number for STP, and 1) a Protocol Number for STP, and
2) an IPv6 Link-Local Scope multicast address for All-STP- 2) an IPv6 Link-Local Scope multicast address for All-STP-
Speakers. Speakers.
Draft ND Proxy November 2004
9. Security Considerations 9. Security Considerations
Proxies are susceptible to the same kind of security issues that Proxies are susceptible to the same kind of security issues that
plague hosts using unsecured Neighbor Discovery or ARP. Even if plague hosts using unsecured Neighbor Discovery or ARP. Even if
these protocols are secured, the proxies may process unsecured these protocols are secured, the proxies may process unsecured
messages, and update the neighbor cache. Malicious nodes within messages, and update the neighbor cache. Malicious nodes within
the subnet can take advantage of this property, and hijack the subnet can take advantage of this property, and hijack
traffic. The threats are discussed in detail in [PSREQ]. traffic. The threats are discussed in detail in [PSREQ].
As a result, securing Neighbor Discovery or ARP must take into As a result, securing Neighbor Discovery or ARP must take into
account the ability to proxy messages. This document does not account the ability to proxy messages. This document does not
introduce any new requirements in this regard. introduce any new requirements in this regard.
From an IPv6 perspective, RFC 2461 [ND] already defines the From an IPv6 perspective, RFC 2461 [ND] already defines the
ability to proxy Neighbor Advertisements. The requirements for ability to proxy Neighbor Advertisements. Since the ND packets
securing proxied messages are similar to those for securing Router must be modified whenever the link-layer address formats are
Advertisements, since the receiver must verify that the different (as with PPP) or promiscuous reception is not possible
advertisement came from a valid router/proxy, rather than from the (as with 802.11), securing any solution in this space requires
owner of a specific address. that hosts have a secure relationship with the proxy.
It is reasonable for nodes on the leaf subnet to have a secure
relationship with the proxy, and accept ND packets from either the
owner of a specific address (normal SEND), or which it can verify
are from a trusted proxy (see below).
For nodes on the external subnet, there is a tradeoff between
security (where all nodes have a secure relationship with the
proxy) and privacy (where no nodes are aware that the proxy is a
proxy). In the case of a point-to-point external link (Scenario
2) however, SEND may not be a requirement on that link.
Verifying that ND packets come from a trusted proxy requires an
Draft ND Proxy February 2005
extension to the SEND protocol and is left for future work, but is
similar to the problem of securing Router Advertisements which is
supported today.
10. Appendix A: Comparison with Naive RA Proxy 10. Appendix A: Comparison with Naive RA Proxy
It has been suggested that a simple Router Advertisement (RA) It has been suggested that a simple Router Advertisement (RA)
proxy would be sufficient, where the subnet prefix in an RA is proxy would be sufficient, where the subnet prefix in an RA is
"stolen" by the proxy and applied to a downstream link instead of "stolen" by the proxy and applied to a downstream link instead of
an upstream link. Other ND messages are not proxied. an upstream link. Other ND messages are not proxied.
There are many problems with this approach. First, it requires There are many problems with this approach. First, it requires
cooperation from all nodes on the upstream link. No node cooperation from all nodes on the upstream link. No node
skipping to change at page 15, line 4 skipping to change at page 16, line 35
upstream link. Similarly, if messages are not proxied during DAD, upstream link. Similarly, if messages are not proxied during DAD,
conflicts can occur. conflicts can occur.
Second, if the proxy assumes that no nodes on the upstream link Second, if the proxy assumes that no nodes on the upstream link
have addresses in the prefix, such a proxy could not be safely have addresses in the prefix, such a proxy could not be safely
deployed without cooperation from the network administrator since deployed without cooperation from the network administrator since
it introduces a requirement that the router itself not have an it introduces a requirement that the router itself not have an
address in the prefix. This rules out use in situations where address in the prefix. This rules out use in situations where
bridges and Network Address Translators (NATs) are used today, bridges and Network Address Translators (NATs) are used today,
which is the problem this document is directly addressing. which is the problem this document is directly addressing.
Draft ND Proxy November 2004
Instead, where a prefix is desired for use on one or more Instead, where a prefix is desired for use on one or more
downstream links in cooperation with the network administrator, downstream links in cooperation with the network administrator,
Prefix Delegation [PD] should be used instead. Prefix Delegation [PD] should be used instead.
11. Authors' Addresses 11. Authors' Addresses
Dave Thaler Dave Thaler
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052-6399 Redmond, WA 98052-6399
Phone: +1 425 703 8835 Phone: +1 425 703 8835
EMail: dthaler@microsoft.com EMail: dthaler@microsoft.com
Mohit Talwar Mohit Talwar
Microsoft Corporation Microsoft Corporation
Draft ND Proxy February 2005
One Microsoft Way One Microsoft Way
Redmond, WA 98052-6399 Redmond, WA 98052-6399
Phone: +1 425 705 3131 Phone: +1 425 705 3131
EMail: mohitt@microsoft.com EMail: mohitt@microsoft.com
Chirayu Patel Chirayu Patel
All Play, No Work All Play, No Work
Bangalore, Karnataka 560038 Bangalore, Karnataka 560038
Phone: +91-98452-88078 Phone: +91-98452-88078
EMail: chirayu@chirayu.org EMail: chirayu@chirayu.org
skipping to change at page 16, line 4 skipping to change at page 17, line 31
D. Plummer, "An Ethernet Address Resolution Protocol", STD D. Plummer, "An Ethernet Address Resolution Protocol", STD
37, RFC 826, November 1982. 37, RFC 826, November 1982.
[BRIDGE] [BRIDGE]
T. Jeffree, editor, "Media Access Control (MAC) Bridges", T. Jeffree, editor, "Media Access Control (MAC) Bridges",
ANSI/IEEE Std 802.1D, 1998, ANSI/IEEE Std 802.1D, 1998,
http://standards.ieee.org/getieee802/download/802.1D-1998.pdf. http://standards.ieee.org/getieee802/download/802.1D-1998.pdf.
[DHCPv4] [DHCPv4]
R. Droms, "Dynamic Host Configuration Protocol", RFC 2131, R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
Draft ND Proxy November 2004
March 1997. March 1997.
[ICMPv6] [ICMPv6]
Conta, A. and S. Deering, "Internet Control Message Protocol Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6) (ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998. Specification", RFC 2463, December 1998.
[KEYWORDS] [KEYWORDS]
S. Bradner, "Key words for use in RFCs to Indicate S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March, 1997. Requirement Levels", BCP 14, RFC 2119, March, 1997.
[ND] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery [ND] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998. for IP Version 6 (IPv6)", RFC 2461, December 1998.
Draft ND Proxy February 2005
[NODEREQ] [NODEREQ]
J. Loughney, "IPv6 Node Requirements", Work in progress, J. Loughney, "IPv6 Node Requirements", Work in progress,
draft-ietf-ipv6-node-requirements-11.txt, August 2004. draft-ietf-ipv6-node-requirements-11.txt, August 2004.
13. Informative References 13. Informative References
[6TO4] [6TO4]
Carpenter, B. and K. Moore, "Connection of IPv6 Domains via Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001. IPv4 Clouds", RFC 3056, February 2001.
[DHCPAUTH]
Droms, R. and W. Arbaugh, Eds., "Autentication for DHCP
Messages", RFC 3118, June 2001.
[DHCPv6] [DHCPv6]
Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C. Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C.
and M. Carney, "Dynamic Host Configuration Protocol for IPv6 and M. Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003. (DHCPv6)", RFC 3315, July 2003.
[NAT] [NAT]
Srisuresh, P. and K. Egevang, "Traditional IP Network Address Srisuresh, P. and K. Egevang, "Traditional IP Network Address
Translator (Traditional NAT)", RFC 3022, January 2001. Translator (Traditional NAT)", RFC 3022, January 2001.
[PD] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host [PD] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633, December Configuration Protocol (DHCP) version 6", RFC 3633, December
2003. 2003.
Draft ND Proxy November 2004
[PSREQ] [PSREQ]
Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756, May 2004. Discovery (ND) Trust Models and Threats", RFC 3756, May 2004.
14. Full Copyright Statement 14. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is Copyright (C) The Internet Society (2005). This document is
subject to the rights, licenses and restrictions contained in BCP subject to the rights, licenses and restrictions contained in BCP
78, and except as set forth therein, the authors retain all their 78, and except as set forth therein, the authors retain all their
rights. rights.
Draft ND Proxy February 2005
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. PARTICULAR PURPOSE.
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