IS-IS WG - IETF 71 Summary Route with Detailed Reachability George Swallow, Clarence Filsfils, Stefano Previdi

2 Motivation Scalability and convergence IGP convergence SPT Calculation is quick FIB update is not so quick Would like to summarize routes in FIB BGP Convergence Next hop tracking very useful Depends on reachability to /32 address Currently IS-IS makes no distinction between having a route and having reachability Want to have it both ways!

3 L3VPN over L2TPv3 VPN packets are encapsulated in L2TPv3 For many VPNs, multiple next-hops are carried in BGP using a Route Distinguisher (RD) Switch to new route occurs on BGP withdrawal or indication from ISIS that the next-hop is not reachable (aka BGP NH tracking) To scale IS-IS, operators would like to summarize PE loopbacks However summarizing hides detailed reachability, BGP convergence then depends on BGP withdrawal Area 0 Area 1 ABR1PE Area 2 PE Area 3 PE3ABR ABR2

4 Separating Routing and Reachability New routing advertisement - SRDR Summarized route Detailed reachability Proposed format Use the Extended IP Reachability TLV Add a sub-TLV Bit vector of reachable hosts Vector length = 2^(number of ignored bits)

5 Example Area 2 has /25 assigned as its address range The following addresses appear in ABR2’s database for Area then the bit mask encoding would advertise a summary route to /25 with an associated 128-bit mask like this:

6 Changes in draft-…-01 Added applicability section case study as motivation for sufficiency of bit-map encoding Added text on partitioning

7 Bit-Vector Characteristics Limited to 1024 bits by TLV/sub-TLV encoding Fixed size Good for memory mgmt Good for LSP fragmentation issues Cannot exceed allowable sub-TLV size Not compact for sparse allocation Works well for IPv4 given the assumptions in the following case study

8 Bit-Vector Case Study Assume up to 30k routers in network Break this into 75 domains Average of 400 routers / domain Assume PE are numbered in blocks of /24 addresses Utilized 33% due to admin inefficiency Requires 5 /24 per domain = 375 total Each /24 would need 32 bytes of bit-vector ~ 12k bytes total Much less than advertising the /32s

9 Inconsistent Advertisements “Should” only happen in two cases Race condition between L1L2 routers seeing a host/router come up or down Area partition Solution Monitor bit vector associated with any summary address matching one that you are advertising Leak /32 for hosts seen by you but not by some other L1L2 advertising this summary Appropriate hold-downs apply

10 Detailed Reachabilty Encoding These assumptions should carry over to IPv6 if provides allocate loopbacks from /120 addresses Authors would like feedback on the assumptions from Service Providers

11 Inconsistent Advertisements L1 PE L1 PE How do ABR1, ABR2 react to inconsistent advertisements from ABR3, AB4? How does PE1 react to inconsistent advertisements from ABR1, ABR2 ABR1 & ABR2 adversize logical of bit-masks and leak any covered /32s PEs select most specific address L2 Domain ABR1ABR3ABR4ABR2