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INTERNET DRAFT                                          S. Bandyopadhyay
draft-shyam-site-multi-40.txt                             March 26, 2017
Intended status: Experimental
Expires: September 26, 2017


         Solution for Site Multihoming in a Real IP Environment
                     draft-shyam-site-multi-40.txt

Abstract

   This document provides a solution for Site Multihoming of stub
   networks in a real IP environment. Each user interface in a customer
   network may have as many global unicast addresses as many service
   providers it will be connected with. Users can establish multiple
   connections through different service providers simultaneously.
   Customer networks can maintain private address space to communicate
   within its users. Customer networks can provide IP mobility services
   as well.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on September 26, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.



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Table of Contents
   1. Introduction.....................................................2
   2. Solution for site multihoming....................................3
   2.1. Multihoming and IP Mobility....................................5
   2.2. Selection of source and destination address ...................6
   2.2.1. Path selection...............................................7
   2.2.2. Link failure and switch over to an alternate route...........8
   2.3. Implementation aspects........................................13
   2.3.1. Processing of system call 'getcommaddr'.....................14
   2.3.2. Processing of 'gethostbynamewithsrcaddr'....................16
   2.3.3. Changes required in ip_output and ip_forwarding modules.....18
   2.3.4. Processing of protocol input routines and socket IO
          system calls................................................18
   2.4. Multihoming and VPN...........................................19
   2.5. IP Address Stacking...........................................19
   3. Security Consideration..........................................23
   4. IANA Consideration..............................................23
   5. Normative References............................................23
   6. Informative References..........................................24
   7. Author's Address................................................24

1. Introduction

   Based on the definition of "multihoming" as stated in RFC3582[1],

   "A "multihomed" site is one with more than one transit provider.
   "Site-multihoming" is the practice of arranging a site to be
   multihomed."

   This is a general solution for site multihoming of stub networks in a
   real IP world irrespective of the framework supported by the service
   provider network.  The solution is applicable to any customer network
   that receives globally unique IP addresses for all of its nodes and
   communicates with the rest of the world without the help of NAT[15].
   It is applicable to any version of IP, i.e. IPv4, IPv6 or any new
   generation of IP that may emerge by removing the drawbacks associated
   with IPv6[7]. Within a provider assigned address space, each customer
   network will possess as many global unicast address space as many
   service providers it gets connected with.  So, an user interface of a
   host may have as many global unicast addresses as many service
   providers it will be connected with.

   Users can maintain multiple connections through multiple service
   providers simultaneously. A customer network can maintain private IP
   addresses to communicate within its users. Communication using
   private IP is restricted to private IP space for the sake of privacy.
   Customer networks can provide IP mobility support as well.




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   There are many variants of UNIX systems (as well as real time
   operating systems) which make use of BSD source code for their
   implementation of TCP/IP stack.  The solution given below highlights
   the changes required with the BSD release 4.4 source code with the
   notations used by IPv4. It addresses issues relevant to IPv6 wherever
   applicable.  All other implementations of TCP/IP have to be updated
   in the similar manner.

   In this document the term "default router" will refer to the customer
   edge (CE) router that communicates with the provider network. Also
   the term "intermediate routers" will refer to all the routers apart
   from the CE routers.

2. Solution for site multihoming

   RFC1122[2] made an extensive study related to different aspects of
   multihoming.  Some of the requirements suggested in that document
   related to UDP and the application layer were avoided for multihomed
   hosts in a connected network with a single gateway to reach the
   outside world. This was achieved by the implementation of TCP/IP by
   making sure that the interface address of an outgoing packet gets
   selected based on the route to be followed by the destination
   address. This criterion holds good in a connected environment with a
   single gateway to reach the outside world. Once more than one gateway
   comes into play to reach the outside world, either routing table of
   the entire world has to be brought in or needs some enhancements
   within the existing system to make the things work.

   Whenever a customer network gets service from more than one service
   provider, the customer network can be viewed as having multiple
   source-id (user-id) space.  Each of these IP domain gets connected to
   different service providers through different routers. So each
   interface of customer network may have as many global unicast
   addresses as many service providers it is connected with. Number of
   routing entries in the routing table will (roughly) become a multiple
   of IP domains that it supports. Communication between any two hosts
   within the customer network will follow the traditional routing
   mechanism. In order to provide multihoming services it is needed that
   a host computer always forwards packets to the customer edge router
   associated to the same IP domain while communicating to someone in
   the outside world. i.e. if the interface of a host computer H
   receives an IP address 'addr1' and 'addr2' from two service providers
   P1 and P2 which are connected through routers R1 and R2 respectively,
   host H has to forward a packet to R1 while using its IP address as
   'addr1' in order to send packets to the outside world. So, host
   computers as well as the intermediate routers have to use default
   routing based on the source domain of the source address in the IP
   header.



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   In order to achieve this, host computers as well as intermediate
   routers need to have information related to its IP domain (net
   address/net mask) and the associated default router for all of its IP
   domains. They need to have a route entry per IP domain for all of its
   default routers. These information should be uploaded at the system
   start up time.

   Routing of IP packets (in the ip_output module of the hosts and in
   the ip_forwarding module of the intermediate routers) need to be
   modified in the following manner.

   If destination address of a packet falls outside of its IP domains,
   it has to be forwarded to the default router based on the domain that
   the source address belongs to.

   If destination address of the IP header falls within any one of its
   IP domains, usual routing mechanism has to be followed.

   If customer network maintains private IP domain, communication using
   private IP has to be restricted within private IP space.

   UDP (or RAW) based servers that need to support multiple clients
   simultaneously need to respond to a client's request with the same
   source address that the client had specified as the destination
   address. In order to satisfy this, system needs to introduce two
   system calls along with the existing system calls (i.e. read, write,
   send, sendto, recv, recvfrom)

   ssize_t recvwithdstaddr (int sockfd, char *buf, size_t nbytes,
       int flags, struct sockaddr *from, socklen_t *fromlen,
       struct sockaddr *fromcladdr, socklen_t *fromcladdrlen,
       struct sockaddr *dst, socklen_t *dstlen,
       struct sockaddr *dstcladdr, socklen_t *dstcladdrlen);

   'recvwithdstaddr' receives data with destination address as specified
   by the sender. It is similar to 'recvfrom' with the additional field
   'dst' related to the address of the receiving interface of the host.
   'fromcladdr' and 'dstcladdr' will hold the values of co-located care-
   of addresses (see section 2.2) of source and destination if they
   happen to be mobile.

   ssize_t sendwithsrcaddr (int sockfd, char *buf, size_t nbytes,
       int flags, struct sockaddr *to, socklen_t tolen,
       struct sockaddr *dstcladdr, socklen_t dstcladdrlen,
       struct sockaddr *src, socklen_t srclen,
       struct sockaddr *srccladdr, socklen_t srccladdrlen);

   'sendwithsrcaddr' sends data specifying the source address of the



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   outgoing interface of the host. It is similar to 'sendto' with
   additional parameters related to source address. It behaves like
   'sendto' if no address is specified for 'src'. 'srccladdr' and
   'dstcladdr' will hold the values of co-located care-of addresses of
   source and destination.

   All the UDP based servers that need to support multiple clients
   simultaneously, need to replace 'sendto' with 'sendwithsrcaddr' and
   'recvfrom' with 'recvwithdstaddr'.

   It has been expressed in several documents including RFC4291[3], that
   a single interface will possess multiple IP addresses in a real IP
   environment.  In these cases, all the UDP servers have to be updated
   with the system calls 'sendwithsrcaddr' and 'recvwithdstaddr' even if
   a customer site gets attached to a single gateway to reach the
   outside world.

   The same logic will apply to server applications with RAW sockets.
   Server applications that are TCP based should work in the usual
   manner.

2.1. Multihoming and IP Mobility

   For a mobile node, its co-located care-of IP address[4] has to be
   bound to one of the IP addresses supported by the service providers
   (if mobile node advertises more than one address, the home agent will
   get confused, also there are other implications).  Transport layer
   must ensure that the 'home address' gets tightly coupled with that
   particular IP address.

   A mobile node in a foreign site will have all the IP addresses
   supported by the foreign site as well as its "Home Address".  As the
   mobile node will also communicate with the outside world with its
   "Home Address", user should get a provision to choose its "Home
   Address" while initiating communication. If mobile node makes use of
   the address of foreign site for applications that do not need its
   "Home Address" (say, accessing a web site) cost of communication will
   get reduced. This feature is useful when a mobile user is in a
   foreign site but remains within the same sphere of influence (say an
   user lives in one city but works in a different city which is in a
   different sphere of influence and likes to access web during his
   working hours).

   If "Home Address" is selected for communication, the transport layer
   of the mobile node should use its care-of address as the source
   address and pass its "Home Address" as an option field in the stack.
   This is because multihoming expects the source address as the
   deciding factor for packet forwarding.



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   All the issues that need to be handled for IP mobility have been
   thoroughly discussed in section 5 of the architectural
   specification[7]. Please go through that section first before going
   through the rest.

2.2. Selection of source and destination address

   If a source network is connected with 'n' service providers and the
   destination network is connected with 'm' service providers, there
   will be a possible 'm*n' combination of source-destination pairs for
   connection between source and destination. So, application program
   needs to select a source and destination address before initiating
   communication with the destination.

   A system call needs to be introduced to get the source address based
   on the destination address. If application program needs to use the
   destination address directly, it needs to use this system call.

   int getcommaddr(int sockfd, struct in_addr *dst, struct addr_pair
   *endpts);

   'addr_pair' holds the addresses of communication end points as
   follows:

   struct addr_pair {
       struct in_addr src;
       struct in_addr dst;
   };

   'getcommaddr' returns the number of source-destination pairs for
   communication; the field 'endpt' will hold the array of these
   addresses. The array will be in sorted manner based on the best
   possible route.  'sockfd' is used to get the 'type of service'
   assigned. So, an application program needs to set its type of service
   before using this call.

   Users may use name instead of IP address to reach the destination.  A
   new system call needs to be introduced 'gethostbynamewithsrcaddr',
   which is an extension to 'gethostbyname' as follows:

   struct hostent *gethostbynamewithsrcaddr(int sockfd,const char *name,
                  int *nroutes, struct addr_pair *endpts);

   'gethostbynamewithsrcaddr' takes 'name' and 'sockfd' as input
   parameters and finds out the best possible route to reach the
   destination. It returns the pointer to the 'hostent' structure as
   returned by 'gethostbyname' system call.  The parameter 'nroutes'
   gets the number of possible routes to be used and the corresponding



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   source and destination addresses gets assigned to 'endpts' in sorted
   manner. 'sockfd' is used to get the 'type of service' assigned. So,
   an application program needs to set its type of service before using
   this call.

   An application program needs to use these source addresses from the
   top (i.e. the 0th) to establish connection with the destination. It
   needs to bind source address 'src' and then connect with the
   destination address 'dst'.

2.2.1. Path selection

   Paths are selected by sending RSVP messages from user to the PE
   routers using MPLS UNI[12] with the following changes in respective
   modules.

   In order to transport a packet from one network to another, provider
   network sets up a LSP. In RSVP[10,11], resource reservation is
   receiver-initiated. In the Path message, the sending application
   construct Path message using RSVP SENDER_TSPEC and ADSPEC objects.
   The path properties of ADSPEC object gets modified by the network
   elements as the Path message moves from sender to receiver. The
   receiver makes use of SENDER_TSPEC and ADSPEC objects and forms
   FLOWSPEC object and sends back to the network element towards the
   sender. In order to make decision which path an application should
   select from multiple possible paths due to multihoming, ADSPEC object
   that was received by the receiver has to be passed back to the sender
   by appending them with the Resv message.

   For best effort service, path is selected based on widest-shortest
   path approach, i.e. the path having the maximum effective available
   bandwidth with minimum NUMBER_OF_IS_HOPS. Effective available
   bandwidth is calculated as

     bandwidth allocated to the customer
   ----------------------------------------- * AVAILABLE_PATH_BANDWIDTH
   gross effective bandwidth allocated to customers

   If (Effective available bandwidth > unused bandwidth
                                       allocated to the customer)
       Effective available bandwidth = unused bandwidth
                                       allocated to the customer.

   When a Path message is sent from a user to the ingress PE router, for
   best-effort service the PE router sets up a LSP with the egress PE
   router and stores the path attributes with the ADSPEC objects if no
   LSP has already been created. The ingress PE router sends the path
   attributes (with AVAILABLE_PATH_BANDWIDTH set as Effective available



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   bandwidth) to the sender. If ingress PE router finds an existing LSP
   for the destination node, it sends the path attributes associated to
   the LSP.

   PE routers need to maintain a list of customers that have accessed
   the LSP with the last time of access. At the end of each RSVP refresh
   time, it needs to check the list and delete those entries whose last
   time of access exceeds the time period of RSVP refresh time. Gross
   effective bandwidth is calculated as the sum of bandwidths allocated
   to all the customers available in the list.

   The above equation is applicable when communication takes place
   between global unicast/multicast addresses. In case of VPN, service
   providers allocate fixed bandwidth path between two customer
   locations. So, when communication takes place between private
   addresses actual unused bandwidth of that path has to be returned.

   For Guaranteed bandwidth[14] and Controlled-Load service[13] path is
   selected with MINIMUM_PATH_LATENCY with minimum NUMBER_OF_IS_HOPS,
   also sender applications need to send PathTear messages for all the
   paths that are not selected.

   A PE router will be in a different address space than the address
   space of the customer network. As hosts need not be aware of the PE
   routers, hosts need to send queries to the CE router to get the
   address of the PE router and store the same in their cache, the way
   it works with DNS.

2.2.2. Link failure and switch over to an alternate route

   As stated in section 2.1, there are possible "m*n" routes.  Client
   applications select any one of them for communication. If
   communication fails due to link failure, it may be desirable to
   switch over to an alternate route (application programs must ensure
   that it conforms to the requirement of the application).

   In reality link failure is a rare phenomenon; so detection of link
   failure should not become an overhead for the network. Fault gets
   detected first at the local site where the fault is associated with.
   Say, if CE-PE link fails, it is the CE router that comes to know
   about it at the beginning. So, the local site needs to take
   initiative for the switchover operation.  When failure happens,
   system generates trap which triggers the operation for switchover to
   an alternate route.

   The steps can be summarized as follows:

   o When client application calls 'getcommaddr' or



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   'gethostbynamewithsrcaddr' system finds out a list of possible
   "source-destination" pairs for communication. If number of routes
   happen to be more than one rest of the steps are followed.

   o Client application establishes a TLS [5] session with its peer
   after 5 unit tuple gets established. After handshake operation,
   client application sends the list of source-destination pair to its
   peer in secured mode. Exchange of routes is required because failure
   may happen in the remote site too;

   o Both client application and its peer store security parameters of
   TLS session and the list of source-destination routes with the
   protocol control block (PCB) using 'setsockopt' which informs the
   system to activate switchover operation if there is a link failure;

   o When CE router detects failure of CE-PE link, it broadcasts an ICMP
   message ICMP_LINKFAILURE_CE_PE_LINK to all the hosts.

   o On receiving ICMP_LINKFAILURE_CE_PE_LINK, system goes through the
   list of PCB and gets the list of applications for which it needs to
   start the switchover operation.  For any such particular application,
   it prepares the list of possible routes for communication through the
   active links. It tries to set alternate route to its peer by sending
   ICMP message ICMP_LINKFAILURE_SET_ALT_ROUTE in secured mode with the
   best possible route.

   o On receiving ICMP_LINKFAILURE_SET_ALT_ROUTE, peer host checks
   whether there is any application in the list of PCB where the request
   will be applicable. On finding the right PCB, it sets the alternate
   route and sends a message ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED to
   its peer.

   o On receiving ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED, system sets
   the alternate route and completes the operation of switchover.

   So, it introduces an ICMP message of type ICMP_LINKFAILURE (type 41)
   with the following codes:
      ICMP_LINKFAILURE_CE_PE_LINK              1
      ICMP_LINKFAILURE_CE_FAILURE              2
      ICMP_LINKFAILURE_SET_ALT_ROUTE           3
      ICMP_LINKFAILURE_ALT_ROUTE_ESTABLISHED   4

   In order to provide secured communication it needs to depend on
   security protocol SSL/TLS.  Security parameters e.g. secret key,
   compression method and cipher spec are stored in the PCB. ICMP
   messages will have two parts; information in the first part, i.e.
   'struct icmp' will hold all the necessary information to locate the
   connection entry in the list of PCB. The second part will hold the



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   information related to the operation and will be in encrypted form
   with record header.  So, changes within a PCB entry is allowed only
   if ICMP message is received in a secured mode.

   It introduces an element 'struct id_pcb' inside union 'icmp_dun' of
   'struct icmp' as follows:

   struct icmp {
      u_char   icmp_type;   /* type of message, see below */
      u_char   icmp_code;   /* type sub code */
      u_short  icmp_cksum;  /* ones complement cksum of struct */
      union {
         u_char ih_pptr;   /* ICMP_PARAMPROB */
         struct in_addr ih_gwaddr;    /* ICMP_REDIRECT */
         struct ih_idseq {
            uint16_t   icd_id;    /* network format */
            uint16_t   icd_seq; /* network format */
         } ih_idseq;
         int ih_void;
         /* ICMP_UNREACH_NEEDFRAG -- Path MTU Discovery (RFC1191) */
         struct ih_pmtu {
            uint16_t ipm_void;     /* network format */
            uint16_t ipm_nextmtu;     /* network format */
         } ih_pmtu;
         struct ih_rtradv {
            u_char irt_num_addrs;
            u_char irt_wpa;
            u_int16_t irt_lifetime;
         } ih_rtradv;
      } icmp_hun;
      union {
         struct id_ts {           /* ICMP Timestamp */
            uint32_t its_otime;   /* Originate */
            uint32_t its_rtime;   /* Receive */
            uint32_t its_ttime;   /* Transmit */
         } id_ts;
         struct id_ip  {
            struct ip idi_ip;
                        /* options and then 64 bits of data */
         } id_ip;
         struct id_pcb {
            u_char ipcb_ip_proto;      /* protocol TCP/UDP    */
            struct in_addr ipcb_laddr, /* source address      */
                           ipcb_faddr; /* destination address */
            u_short ipcb_lport,        /* source port         */
                    ipcb_fport;        /* destination port    */
         } id_pcb;
         struct icmp_ra_addr id_radv;



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         u_int32_t id_mask;
         char     id_data[1];
      } icmp_dun;
    };

   'struct inpcb' of protocol control block includes four new fields
   'inp_lf_n_routes', 'inp_lf_stat', 'inp_lf_routes' and
   'inp_seq_params' of type SecParams (SecParams is a type of struct
   whose elements are elements of SecurityParameters as defined in
   section 6.1 of RFC5246 [5]) as follows:

   struct inpcb {
      struct inpcb *inp_next, *inp_prev;  /* doubly linked list  */
      struct inpcb *inp_head;    /* pointer back to chain of inpcb's for
                                  this protocol */
      struct in_addr inp_faddr;  /* foreign IP address */
      u_short inp_fport;         /* foreign port# */
      struct in_addr inp_laddr;  /* local IP address */
      u_short inp_lport;         /* local port# */
      struct in_addr inp_fcladdr;/* foreign care-of address */
      struct in_addr inp_lcladdr;/* local care-of address */
      struct in_addr inp_hagentaddr; /* address of home agent */
      struct socket *inp_socket; /* back pointer to socket */
      caddr_t inp_ppcb;        /* pointer to per-protocol pcb */
      struct route inp_route   /* placeholder for routing entry */
      int inp_flags;           /* generic IP/datagram flags */
      struct ip inp_ip;        /* header prototype; should have more */
      struct mbuf *inp_options;/* IP options */
      struct ip_moptions *inp_moptions; /* IP multicast options */
      u_char inp_lf_n_routes;  /* number of possible routes */
      u_char inp_lf_stat;      /* state of switchover;
                                STAT_DO_NOT_ALTER(0)/STAT_ALTER(1)  */
      struct addr_pair *inp_lf_routes;/*pointer to the array of routes*/
      SecParams inp_seq_params;/* security parameters */
    };

   From application layer, the field 'inp_seq_params' is set with the
   system call 'setsockopt' by introducing a new socket option
   SO_SEQPARAM of level SOL_SOCKET; route information i.e.
   inp_lf_n_route, inp_lf_routes and inp_lf_stat are set by system call
   'setsockopt' by introducing another socket option SO_LFROUTES of
   level SOL_SOCKET.

   setcockopt (sockfd, SOL_SOCKET, SO_SEQPARAM, (char *)&seq_param,
   sizeof(SecurityParameters));

   setsockopt (sockfd, SOL_SOCKET, SO_LFROUTES, (char *)routes, sizeof
   (struct addr_pair)*n_routes);



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   ICMP messages with 'icmp_code' ICMP_LINKFAILURE_SET_ALT_ROUTE and
   ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED will have same format as
   follows:

   Information of the current active link of the PCB entry i.e. protocol
   id, source address, destination address, source port and destination
   port are set with the fields of 'struct id_pcb' of 'struct icmp'. The
   encrypted part of the message will have three fields, source address
   and destination address of the alternate route and ICMP code (i.e.
   ICMP_LINKFAILURE_SET_ALT_ROUTE/
   ICMP_LINKFAILURE_ALT_ROUTES_ESTABLISHED) as it was set with the ICMP
   header.

   Recipient of these messages needs to search PCB entry in the
   following manner:

   If 'source port', 'destination port' and 'protocol id' of incoming
   ICMP message matches with any entry in the list of PCB and the fields
   'source address' and 'destination address' of the ICMP message
   matches with any entry of 'inp_lf_routes' of the corresponding entry
   in the PCB, it will be considered as a match. If no matching entry is
   found, message has to be dropped. With the security information of
   the PCB entry, the encrypted part of the ICMP message gets decrypted.
   If it fails to decrypt the message or the message received with
   invalid MAC, message needs to be dropped. If ICMP code in the header
   does not match with that of the encrypted part, the message also
   needs to be dropped.

   Details of the ICMP operations are described below:

   ICMP_LINKFAILURE_CE_PE_LINK

   CE router detects link failure and sends this message to all the
   users in the network; The field 'icmp_gwadd' of 'struct icmp' holds
   the IP address of the PE router.

   ICMP_LINKFAILURE_CE_FAILURE

   CE router itself may fail. It gets detected by alternate CE router.
   CE routers send keep-alive messages between themselves at regular
   interval to detect this failure. The field 'icmp_gwadd' of 'struct
   icmp' holds the IP address of the faulty CE router.

   ICMP_LINKFAILURE_SET_ALT_ROUTE

   This message is sent by a host after receiving ICMP broadcast message
   ICMP_LINKFAILURE_CE_PE_LINK or ICMP_LINKFAILURE_CE_FAILURE from a CE
   router for all the entries of PCB whose ('inp_lf_stat' = STAT_ALTER



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   and source-destination route passes through the failed link), to
   their peer. It maintains a list of information where each entry will
   have the connection details including the best possible route. For
   best effort traffic route is selected by sending echo messages and
   calculating round trip delay; for the rest it follows the approach
   stated in section 2.1.1. For each entry in the list, host sends
   ICMP_LINKFAILURE_SET_ALT_ROUTE for (arbitrary) 'n' number of times
   with an (arbitrary) interval of 't' msecs (sufficient enough for the
   reply of ICMP_LINKFAILURE_SET_ALT_ROUTE comes back and gets
   processed; roughly twice the round trip delay) till it receives a
   positive acknowledgment ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED from
   its peer.  On receiving a positive acknowledgment
   ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED, it deletes the corresponding
   entry from the list and updates the route information in the PCB.

   ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED

   On receiving ICMP_LINKFAILURE_SET_ALT_ROUTE, host needs to look for a
   match in the PCB. If there is a match, host sends
   ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED to its peer on successful
   completion of changing 'source address' and 'destination address'
   with the desired value of the alternate route in the PCB. The message
   will contain all the fields as that of the receiving message by
   setting 'icmp_code' as ICMP_LINKFAILURE_ATL_ROUTE_ESTABLISHED both at
   the header part as well as at the encrypted part.

   Switchover operation requires some amount of time. This duration is
   under the tolerance limit for best effort traffic. For Guaranteed
   bandwidth and Controlled-Load service as the circuit needs to be
   reestablished, it may cause flicker.  This situation can be avoided
   by maintaining back-up circuit through an alternate route. As link
   failure is a rare phenomenon, this feature can be provided on on-
   demand basis or based on the application type.

2.3. Implementation aspects

   Following changes are expected with the source code of BSD.

   Introduce ip_domain structure and some parameters as follows:

       struct ip_domain {
           struct in_addr net_addr;
           struct in_addr net_mask;
           struct in_addr def_router;
       };
       #define MAX_IP_DOMAINS    16
       short num_ipdomains;
       struct ip_domain *ipdomain[MAX_IP_DOMAINS];



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   If customer network maintains private IP domain (along with the user-
   id space provided by the service providers) and expects its
   communication to be confined within its own space, 'def_router' has
   to be set as NULL.

   Upload IP domain information for all of its IP domains during system
   start up.  These domain information can be uploaded through router
   advertisement or through DHCP. The domain information should contain
   the next hop address to reach the corresponding default router as
   well.

   There has to be a provision to upload these information through
   'sysctl' to configure them manually.

   Three new 'sysctl' routines have to be introduced under the 'ip' node
   of the MIB tree (i.e. under CTL_NET, PF_INET, IPPROTO_IP)
   IPCTL_NUM_DOMAINS, IPCTL_DOMAIN and IPCTL_USE_HOMEADDR (applicable
   for mobile node). Both IPCTL_NUM_DOMAINS and IPCTL_USE_HOMEADDR are
   of type CTLTYPE_INT and IPCTL_DOMAIN is of type CTLTYPE_NODE. Using
   'sysctl' IPCTL_NUM_DOMAINS has to be configured first. Configuration
   of IPCTL_NUM_DOMAINS has to populate IPCTL_NUM_DOMAIN entries of
   nodes under IPCTL_DOMAIN and for each of these nodes three MIB
   attributes DOMAIN_NET_ADDR, DOMAIN_NET_MASK and DOMAIN_DEF_ROUTER
   (each of type CTLTYPE_NODE) has to be allocated.

   All the routers as well as hosts that are having interfaces
   connecting to multiple subnets need to be configured through
   'sysctl'.

   Mobile users should get provision to change IPCTL_USE_HOMEADDR
   attribute dynamically.

   Add a route entry for all the default routers during system start up.

2.3.1. Processing of system call 'getcommaddr'

   Introduce a routine (say 'getendpointaddr') that will find out a list
   of source-destination addressees sorted in order based on sending
   Path messages between a list of source addresses to a list of
   destination addresses.  The routine should select the service type
   based on the type of service field (which can be obtained by calling
   'getsockopt' with the socket id 'sockfd' passed as a parameter).

   System call 'getcommaddr' has to be processed in the following
   manner:

   If destination address of the IP packet falls outside of its
   IP domains {



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      If destination address is from private address space {
         if the host is having only one interface {
            for each private address assigned to the interface get
            an entry for the source list.
         }
         else {
            for all the default routers {
               use 'rtalloc' to get the next hop address for the
               default router.

               get an entry for the source list based on
               the outgoing interface 'ia', and the private
               address associated with the default router.
            }
         }
         destination list will have a lone entry with the
         destination private address.
      }
      else {
         If destination address is provider independent {
            call 'getmappedaddr' to get all the associated PA addresses;
            for each PA address get an entry of the destination list
         }
         else {
            get a lone entry for the destination list with the
            destination address.
         }

         If user has selected its "Home Address" {
            /*Applicable to IP mobility*/
            get a lone entry in the source list with the "Home Address".
         }
         else {
            if the host is having only one interface {
               for each global unicast address of the interface,
               get an entry for the source list.
            }
            else {
               for all the default routers {
                  use 'rtalloc' to get the next hop address for the
                  default router.

                  get an entry for the source list based on
                  the outgoing interface 'ia', and the global unicast
                  address associated with the default router.
               }
            }
         }



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      }
      call 'getendpointaddr' to get the list of source-destination
      addresses in sorted manner.
   }
   else { /* i.e. destination address is inside its IP domains */
      use 'rtalloc' to get the next hop address for the
      destination address.

      if destination address is a link local address {
         select source address based on the outgoing interface
         and the link local address assigned to it.
      }
      else {
         select source address based on the outgoing interface
         and the domain that the destination address belongs to.
      }
      there is only one possible source-destination combination.
   }

2.3.2. Processing of 'gethostbynamewithsrcaddr'

   System call 'gethostbynamewithsrcaddr' has to be processed in the
   following manner:

   This is an enhancement of the system call 'gethostbyname'.
   'gethostbyname' calls three routines that performs host table search,
   NIS search and DNS search. DNS entry may contain PI address and all
   global unicast PA addresses. Once name is resolved, following
   additions are expected to resolve source-destination pair.

   If 'hostent' structure contains addresses which are inside its IP
   domains {
      if 'hostent' structure contains a private address {
         Assign destination address as a private address
         contained in 'hostent';

         use 'rtalloc' to get the next hop address for the
         destination address.

         select source address based on the outgoing interface
         and the domain that the destination address belongs to.
      }
      else {
         Select a global unicast address contained in 'hostent' for
         destination address.

         use 'rtalloc' to get the next hop address for the
         destination address.



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         select source address based on the outgoing interface
         and the domain that the destination address belongs to.
      }
      there is only one possible source-destination combination.
   }
   else {
      if 'hostent' structure contains private address {
         if host is having only one interface {
            for each private address assigned to the interface get
            an entry for the source list.
         }
         else {
            for all the default routers {
               use 'rtalloc' to get the next hop address for the
               default router.

               get an entry for the source list based on
               the outgoing interface 'ia', and the private
               address associated with the default router.
            }
         }
         for each private address in the 'hostent' structure
         get an entry for the destination list.
      }
      else {
         for each PA address in the 'hostent' structure
         get an entry for the destination list.

         if user has selected its "Home Address" {
         /*Applicable only to IP mobility */
            get a lone entry in the source list with the "Home Address".
         }
         else {
            if the host is having only one interface {
               for each global unicast address of the interface,
               get an entry for the source list.
            }
            else {
               for all the default routers {
                  use 'rtalloc' to get the next hop address for the
                  default router.

                  get an entry for the source list based on
                  the outgoing interface 'ia', and the global unicast
                  address associated with the default router.
               }
            }
         }



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      }
      call 'getendpointaddr' to get the list of source-destination
      addresses in sorted manner.
   }

2.3.3. Changes required in ip_output and ip_forwarding modules

   Execute the following steps in the 'ip_output' routine of the IP
   stack before it calls 'rtalloc' for route look up.

   If destination address of the IP packet falls outside of its
   IP domains {
       get def router address based on the IP domain
       the source address belongs to.

       use 'rtalloc' to get the next hop address for the def router.

       Forward the packet to the next hop.
   }
   else { /* i.e. destination address is inside its IP domains */
      follow the usual procedure to forward packets
   }

   In BSD, the 'ip_forwarding' routine calls 'ip_output'; so it should
   be left as it is.

2.3.4. Processing of protocol input routines and socket IO system calls

   Protocol input routines need to locate the socket/process in the
   usual manner with the 5 unit tuple (i.e. protocol, source address,
   source port, destination address, destination port).

   When a packet is received by a mobile node (at a foreign site), it
   can be received in two modes. It can be received directly from the
   correspondent node with the 'destination address' as the co-located
   care-of address and its home address in the IP stack (see section 4.1
   of RFC6275[8]). In the second mode the packet can be received via the
   home agent using IP over IP. Once the IP layer receives a packet with
   IP over IP, it is supposed to strip off the outer header before
   passing the packet to the protocol input routine.  In this case
   packet will be received by the protocol input routine with
   destination address as the home address of the mobile node with no
   information related to its care-of address. So, protocol input
   routine needs to check whether the destination address of the
   received packet belongs to any one of its IP domains.  If it does
   not, it needs to find out the co-located care-of address by going
   through the interface list if it is not already found in the packet
   received. This information is needed by the TCP input routine while



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   processing a SYN message. It is also needed by the UDP/RAW modules
   while processing the system call 'recvwithdstaddr'.

   While processing the output routines like 'sendwithsrcaddr',
   'sendto', UDP/RAW modules needs to check the parameters related to
   source address, source port, destination address, destination port,
   care-of address of the source, care-of address of the destination in
   the protocol control block. Parameters in the PCB should prevail over
   parameters passed by the system call while forming the IP packet.

2.4. Multihoming and VPN

   For a corporate, that maintains multiple offices and communicates
   within themselves through private address space using VPN needs to
   distribute its entire private address space to all its site in a
   suitable manner. Each one of its offices will get multiple private
   address space where each of them will be associated with a particular
   link. Let us consider one of its offices gets connected to two
   providers P1 and P2 and gets address space as
   'unicastNetAddr1'/'unicastNetMask1' and
   'unicastNetAddr2'/'unicastNetMask2' respectively. It also gets
   assigned private address space from its corporate as
   'privateDomainNetAddr1'/'privateDomainNetMask1' and
   'privateDomainNetAddr2'/'privateDomainNetMask2' which will be
   associated with the CE routers CE1 and CE2 respectively.

   All hosts as well as the intermediate routers will have four entries
   of ip_domain:

   1: 'net_addr = 'unicastNetAddr1'
      'net_mask = 'unicastNetMask1'
      'def_router = CE1
   2: 'net_addr = 'unicastNetAddr2'
      'net_mask = 'unicastNetMask2'
      'def_router = CE2
   3: 'net_addr' = 'privateDomainNetAddr1'
      'net_mask' = 'privateDomainNetMask1'
      'def_router' = CE1
   4: 'net_addr' = 'privateDomainNetAddr2'
      'net_mask' = 'privateDomainNetMask2'
      'def_router' = CE2

2.5. IP Address Stacking

   IP address stacking in IPv6 is performed with the approach introduced
   in section 6.4 of RFC6275[8] with slight modification. RFC6275
   describes how to pass "Home Address" as well as co-located care-of
   address of the destination address if it happen to be mobile. The



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   same approach has been extended to support IP address stacking for
   the source address and to support IP address stacking for both source
   address as well as destination address.  The "Reserved" space in the
   type 2 routing header has been split into two parts; an one octet
   field to address the "Stacking Type" and the rest 3 octets are left
   as Reserved.

   Stacking Type is interpreted as follows:

   Stacking Type=0
      Source Address: Address of the sender.
      Destination Address: co-located care-of address of the receiver.
      Address 1: Home Address/PI Address of the receiver.
      Hdr Ext Len=2.

   So, type 2 routing header for stacking type 0 will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=2 | Routing Type=2|Segments Left=1|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Stacking Type=0|                Reserved                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +       Address 1:Home Address/PI Address of the receiver       +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Stacking Type=1
      Source Address: co-located care-of address of the sender.
      Destination address: Address of the receiver.
      Address 1: Home Address/PI Address of the sender.
      Hdr Ext Len=2.

   So, type 2 routing header for stacking type 1 will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=2 | Routing Type=2|Segments Left=1|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Stacking Type=1|                Reserved                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +       Address 1:Home Address/PI Address of the sender         +



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   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Stacking Type 2
      Source Address: co-located care-of address of the sender.
      Destination Address: co-located care-of address of the receiver.
      Address 1: Home Address/PI Address of the sender.
      Address 2: Home Address/PI Address of the receiver.
      Hdr Ext Len=4.

   So, type 2 routing header for stacking type 2 will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Header  | Hdr Ext Len=4 | Routing Type=2|Segments Left=1|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Stacking Type=2|                Reserved                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +       Address 1:Home Address/PI Address of the sender         +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +       Address 2:Home Address/PI Address of the receiver       +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Next Header
      8-bit selector.  Identifies the type of header immediately
      following the routing header. Uses the same values as the IPv6
      Next Header field [9].

   Hdr Ext Len
      4 (8-bit unsigned integer);  length of the routing header in 8-
      octet units, not including the first 8 octets.

   Routing Type
      2 (8-bit unsigned integer).




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   Segments Left
      1 (8-bit unsigned integer).

   Stacking Type
      2 (8-bit unsigned integer).

   Reserved
      24-bit reserved field.  The value MUST be initialized to zero by
      the sender, and MUST be ignored by the receiver.

   Address 1
      Home Address/PI Address of the sender.

   Address 2
      Home Address/PI Address of the receiver.

   IP address stacking in IPv4 is performed by introducing new IP option
   under the option class "Datagram or Network Control", i.e. 0. The
   option number is 16. The CODE(144) field is followed by one octet
   field "Stacking Type" followed by two octet reserved space (NULL) as
   padding followed by the address fields based on the Stacking Type.

   Stacking Type is interpreted as follows:
   Stacking Type=0
      Source Address: Address of the sender.
      Destination Address: co-located care-of address of the receiver.
      Address 1: Home Address/PI Address of the receiver.
      Header Length:7

   Format of IP address stacking option with stacking type 0
   in the IP header will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  CODE(144)    |Stacking Type=0| Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +       Address 1:Home Address/PI Address of the receiver       +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Stacking Type=1
      Source Address: co-located care-of address of the sender.
      Destination Address: Address of the receiver.
      Address 1: Home Address/PI Address of the sender.
      Header Length:7

   Format of IP address stacking option with stacking type 1
   in the IP header will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   |  CODE(144)    |Stacking Type=1| Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +       Address 1:Home Address/PI Address of the sender         +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Stacking Type=2
      Source Address: co-located care-of address of the sender.
      Destination Address: co-located care-of address of the receiver.
      Address 1: Home Address/PI Address of the sender.
      Address 2: Home Address/PI Address of the receiver.
      Header Length:8

   Format of IP address stacking option with stacking type 2
   in the IP header will be as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  CODE(144)    |Stacking Type=2| Reserved                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +       Address 1:Home Address/PI Address of the sender         +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   +       Address 2:Home Address/PI Address of the receiver       +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3. Security Consideration

This document provides a solution for site multihoming of stub networks.
Message exchange between source and destination related to link failure
has to be done in secured mode as explained in section 2.1.2. For common
security related issues that any site may experience, one needs to
consult with the "Site Security Handbook", RFC2196[6]. For issues
related to IP Mobility, section 5 of RFC5944[4] has to be consulted.

4. IANA Consideration

This draft does not request any action from IANA.

5. Normative References

   [1]  J. Abley, B. Black, V. Gill, "Goals for IPv6 Site-Multihoming
        Architectures", RFC3582, August 2003.

   [2]  R. Braden, "Requirements for Internet Hosts -- Communication
        Layers", RFC1122, October 1989.

   [3]  R. Hinden, S. Deering, "IP Version 6 Addressing Architecture.",
        RFC4291, February 2006.

   [4]  C. Perkins, "IP Mobility Support for IPv4, Revised", RFC5944,



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        November 2010.

   [5]  T. Dierks, E. Rescorla, "The Transport Layer Security (TLS)
        Protocol Version 1.2", RFC5246, August 2008.

   [6]  B. Fraser, "Site Security Handbook", RFC2196, September 1997.

   [7]  S. Bandyopadhyay, "An Architectural Framework of the Internet
        for the Real IP World" <draft-shyam-real-ip-framework-28.txt>
        (work in progress).
   [8]  C. Perkins, Ed., D. Johnson, J. Arkko, "Mobility Support in
        IPv6" RFC 6275, July 2011.

   [9]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998.

   [10] L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource ReSerVation
        Protocol (RSVP) -- Version 1 Functional Specification", RFC
        2205, September 1997.

   [11] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G.
        Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels",
        RFC 3209, December 2001.

   [12] G. Swallow, J. Drake, H. Ishimatsu, Y. Rekhter, "Generalized
        Multiprotocol Label Switching (GMPLS) User-Network Interface
        (UNI): Resource ReserVation Protocol-Traffic Engineering
        (RSVP-TE) Support for the Overlay Model", RFC 4208,
        October 2005.

   [13] J. Wroclawski, "Specification of the Controlled-Load Network
        Element Service", RFC 2211, September 1997.

   [14] S. Shenker, C. Partridge, R. Guerin, "Specification of
        Guaranteed Quality of Service", RFC 2212, September 1997.

6. Informative References

   [15] P. Srisuresh, K. Egevang, "Traditional IP Network Address
        Translator (Traditional NAT)", RFC3022, January 2001.

7. Author's Address

   Shyamaprasad Bandyopadhyay
   HL No 205/157/7, Kharagpur 721305, India
   Phone: +91 3222 225137
   e-mail: shyamb66@gmail.com




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