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Inter-Area Route Attribute Extension in IS-IS

Proposed extension in IS-IS for inter-area routing attribute with examples and benefits for enhancing routing information sharing and network resilience in multi-level networks.

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Inter-Area Route Attribute Extension in IS-IS

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  1. Inter-Area Route Attributedraft-shen-isis-interarea-route-attr-00.txt Naiming Shen (naiming@redback.com) Albert Tian (tian@redback.com)Derek Yeung (myeung@procket.com)

  2. Motivation • Topology information is not available between routing levels • Some applications using IGP are not limited within the area/level • Additional routing attributes for redistributed route may help even though the real topology information is lost • Applications, such as Nexthop FRR for IP node protection of the border router, need to know the nexthop of the inter-area routes

  3. Inter-Area Route Attribute Sub-TLV • To be added to IS-IS TLVs 135 and 235 • It includes a list of • Attribute Flag • Router ID • Attribute Flag is a 8 bit field, currently defined, • N bit, Nexthop Bit. • O bit, Origination Bit. • B bit, Non-Best Path Bit.

  4. An Example R3 Route X PLR R2 R1 • R2 and R6 are L1/L2 routers. When R2 leaks the inter-area route X into the level-1 area, it can have the route attribute of nexthop to router R3. R1 can reroute to avoid R2 to reach R3 directly when R2 fails • Each RSP node along the path installs the IP host route in RIB/FIB towards the path nexthop R4 Route X, (nexthop R3) R7 R6 reroute R5  IS-IS level-1   IS-IS level-2 

  5. Conclusion • This simple extension defines a sub-TLV attached to the inter-area IP prefix advertisement • Certain inter-area applications can use this route attribute while the topology information in another level is not available • Sub-TLV code needs to be assigned by IANA • Authors would like to request the adoption as an IS-IS WG document ? • http://www.ietf.org/internet-drafts/draft-shen-isis-interarea-route-attr-00.txt

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