Network Working Group                 Karthikeyan (Samsung Electronics)
Internet Draft                        Srivastav (Samsung Electronics)
Expiration Date: December 2003                            June 2003



                  Auto Summarization in RIPv2

                 draft-karthikeyan-autosummarization-in-ripv2-00.txt


Status of this Memo

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

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Abstract

    This document describes an extensible mechanism that allows a 
    RIPv2 [RIP2] speaker to advertise summarized routes to its peers 
    without changing the format of the RESPONSE message. 

    Summarized routes are carried in RESPONSE message like normal
    RIPv2 routes. Summarized routes are treated as normal routes on 
    the receiving side. No extra provisions are required to discriminate
    between summarized and normal routes.

    The mechanisms described in this document is OPTIONAL and is 
    applicable to all RIPv2 speaking routers, with some modifications 





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    in the routing information base and output processing for storing 
    and advertising summary routes. This mechanism cannot be applied to 
    RIPv1 [RIP1].

1.  Specification of Requirements

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in this 
    document are to be interpreted as described in RFC 2119 [KEY-WORDS]. 

2.  Overview

    In current scenario, due to rapid growth in the internet,large 
    number of routes have to be handled by the routers. In order to 
    improve scalability and efficiency in large networks, routes are 
    summarized.This allows the neighbouring routers to reduce the 
    routing table size and to handle more routes. Auto summarization is 
    enabled when routes cross from classless to classful domain.

    Apart from reducing routing table size, auto summarization can also
    improve the stability of the network. If a router is only 
    advertising a summary route to the next downstream router, then it 
    will not advertise changes relating to specific subnets contained 
    within the summarized range.

    RIPv2 routes that are learnt from the neighbours once found best 
    after running decision process are advertised as such to neighbours.
    The current implementation does not summarize routes.
   
    This document modifies the route information base processing by 
    introducing summary route in addition to the normal RIP routes. The 
    output process of RIP is modified to advertise summary routes and to
    suppress child routes. 

        
3.  Operation

    In the following sections, "Child route" refers to a classless route
    or host route. "Summary route" refers to the classful route which is
    collection of child routes contained within the summarized routes 
    range."Local speaker" refers to a router which is performing route 
    summarization and advertising summary routes."Receiving speaker"
    refers to a router that peers with the Local speaker to accept 
    summary routes.

    Auto Summarization SHOULD be enabled by default in routers running 
    RIPv2.RIPv2 implementations should provide configuration commands to 
    disable and enable auto summarization feature. 

    

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    The following section explain how Local speaker should summarize 
    route and advertise summarized routes.Figure 1 shows RTR-B 
    (Router-B) performing auto summarization when routes cross from 
    classless domain to classful domain. 

   
                                    ------------------------------
                                    |
                                    |
                                    |    +-------+
                                    |    |       |  
                                    |    | RTR-c |
                                    |    |       |
                                    |   /+-------+
                                    |  / 10.1.1.0/26
                                    | /  <--
                                    |/
                                    |    +-------+
                                   /|    |       |  
                                  / |   /| RTR-D |
                                 /  |  / |       |
                                /   | /  +-------+
    ---------------------      /    |/   10.1.1.64/26
      classful domain   |     /     /    <--
                        |    /     /|
    +-------+          +-------+  / |    +-------+
    |       |10.0.0.0/8|       | /  |    |       |
    |RTR-A  |----------| RTR-B |/------- | RTR-E |  classless domain
    |       |  <--     |       |\   |    |       |
    +-------+          +-------+ \  |    +-------+
                        |         \ |    10.1.1.128/26
                        |  <--     \|     <-- 
    ---------------------           |   
                                    |\   +-------+
                                    | \  |       |  
                                    |  \ | RTR-F |
                                    |   \|       |
                                    |    +-------+
                                    |    10.1.1.192/26  
                                    |      <-- 
                                    -----------------------------------
   









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4.  Metric manipulation in the Local speaker

    Summary routes are formed from the best metric of all child routes.

    When a new child route with best metric is learnt or when the metric
    of the current "best child route" changes, summary route metric 
    SHOULD be updated.

    When child route with the best metric is no more active,summary 
    route metric SHOULD be changed to the next best available metric
    of the child route.

    Section 3.9.2 of RIPv2 [RIP2] explains the processing of RESPONSE 
    message and modification of routing information base accordingly. 
    Summary routes are formed and installed into the routing information 
    base as soon as new child RIP routes are inserted into the routing
    information base.

5.  Output Processing in the Local speaker

    Local speaker advertises summary route and suppresses the 
    advertisement of child routes. Section 3.10 of [RIP2] explains the 
    output processing by traversing the routing table where child routes 
    are stored. When auto summarization is enabled,routing information 
    base SHOULD be traversed to advertise only summary routes.

    When child route with best metric is no more active, trigger update 
    for the summary route with the next best metric SHOULD be generated.
    When no more child route exist,trigger update for the summary route 
    with infinity metric MUST be generated.

    Trigger update SHOULD not be generated if there is a change in the
    metric of the child route, which does not affect the summary route.

6.  Route Information Base in the Local speaker

    Implementers MAY store summary routes in separate routing table.
    Separate routing table reduces the time involved in retrieving all 
    the summary routes during output process for sending periodic 
    updates. Otherwise,single routing table that is used for storing 
    both summary and child routes, need to be traversed for sending 
    periodic updates

    There may be case, when Local speaker may learn a classful route. In 
    this case the implementers SHOULD take care to differentiate between 
   



Karthikeyan, Srivastav                                         [Page 4]




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    learnt summary route and summarized classful route. This case can be 
    taken care of by having two route tables as discussed above in this 
    section.Summarized route SHOULD have the nexthop set to the Local 
    speaker address, which summarizes the route. 
    

7. Timer processing in Local speaker

    As summarized routes are not RIP learnt route, it is not necessary
    to maintain route entry timeout timer for the summarized route. 
    Garbage collection timer should be maintained for the summary 
    routes. 


8. Summary route formation in Local speaker

    Child routes stored in the routing table are converted into summary 
    routes by converting subprefixes to the classful network boundary.

    Summary routes SHOULD not be formed in disconnected subnets. If the
    network is composed of disconnected subnets, auto summarization 
    SHOULD be disabled to advertise the subnets.

9. Input Processing in Local speaker

    REQUEST packet in RIP is used to ask for a response containing all 
    or part of router's routing information base. Whenever Local speaker 
    gets request for child route, if child route is available in the 
    routing information base. Local speaker should generate RESPONSE 
    packet for child route with metric as in the routing table.


10. Interface down in Local speaker

    When RIPv2 interface is administratively put down, summary routes 
    formed from the child routes learnt via this interface should be 
    updated with the next best available metric from the child route 
    which fall in this summarized range. If there are no more child 
    routes available, summary route SHOULD be updated with infinity
    metric. Trigger update SHOULD be generated for the updated summary 
    route.








Karthikeyan, Srivastav                                         [Page 5]




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11. Processing of default route in Local speaker

    Default routes SHOULD not be summarized. Default routes are 
    advertised without manipulating metric or nexthop unlike the 
    summarized route.When Local speaker receives REQUEST for default 
    route, RESPONSE should be generated.

12. Processing of host routes in Local speaker

    Host routes are summarized like the child routes. All the 
    summarization rules for child routes are applicable to host routes.

13. Forwarding Information Base updation in Local speaker

    Local Speaker SHOULD update the Forwarding Information Base with 
    child routes.Summary routes SHOULD not be updated in the Forwarding 
    Information Base as auto summarization technique is used to 
    reduce the neighbouring forwarding or routing information base size.

14. Processing in Receiving speaker

    Receiving speaker cannot discriminate the summary routes and child 
    routes. The processing in the Receiving speaker remains unchanged.
    Receiving speaker MUST update the routes as discussed in RIPv2 
    specification.
   
15. Disabling auto summarization in Local speaker

    When auto summarization is disabled,Local speaker SHOULD carry
    out the following steps only if there is no RIP learnt route 
    matching the summarized route.
    
    (1) Summary routes metric SHOULD be updated with infinity metric.
   
    (2) Summary routes modified in step (1) SHOULD be advertised in
        the form of trigger update.

    (3) Garbage collection of the summary route SHOULD be set.

    (4) The suppressed child routes should be advertised. 
   
    If there is matching child route, advertise the suppressed child 
    routes.
        
16. Restrictions to RIPv2 auto summarization
  
    Auto summarization SHOULD be disabled if split horizon is enabled.




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17. Security Considerations

    This document introduces no new security concerns to RIPv2 or other
    specifications referenced in this document.

18. References

    [RIP2] Malkin. G., "RIP Version 2 - Carrying Additional Information"
           ,RFC 1723, Xylogics, November 1994.
    [RIP1] Hedrick. C., "Routing Information Protocol", RFC 1058, 
           Rutgers University, June 1988.
    [KEY-WORDS] Bradner, S., "Key words for use in RFCs to Indicate 
           Requirement Levels", BCP 14, RFC 2119, March 1997.

19. Authoré±· Address

    S.Karthikeyan
    Network Systems Division,
    Samsung India Software Operations,
    Bangalore
    INDIA
    Email: karthiks@samsung.com

    Subodh Srivastava
    Network Systems Division,
    Samsung India Software Operations,
    Bangalore
    INDIA
    Email: subodh@samsung.com


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Expiration Date: December 2003