I’ve recently run into a situation where there was no longer enough space in the FIB to handle both the full IPv4 global table and the full IPv6 global table. We prefer to run a default-free network within this particular SP network, but in this case, until a hardware refresh can happen, we’ll need to adjust that. Given what we knew about the size of both tables, it made more sense to take a default IPv6 route from one transit provider and filter the rest. How we did this isn’t a groundbreaking marvel by any means, but it’s probably worth writing down for someone else to reference since it also applies to IPv4. Since we already have global tables, a request to add IPv6 default to our existing full IPv6 table was made to one transit provider. After that request was fulfilled, filter adjustments were made. It should be note that all of these configs were generated off of Brocade MLX routers, so they may look a tad different than an IOS device. Create a prefix list to reference that will allow default:
ipv6 prefix-list V6-PERMIT-DEFAULT seq 5 permit ::/0Create the route map:
route-map IPv6-TRANSIT-DEFAULT-IN permit 100 match ipv6 address prefix-list IPv6-PERMIT-DEFAULTAdd the route-map to the peer:
neighbor 2001:fd8:e00::2 route-map in IPv6-TRANSIT-DEFAULT-INBefore:
Neighbor Address AS# State Time Rt:Accepted Filtered Sent ToSend 2001:fd8:e00::2 65001 ESTAB 15d10h34m 12003 0 14 0After:
Neighbor Address AS# State Time Rt:Accepted Filtered Sent ToSend 2001:fd8:e00::2 65001 ESTAB 15d10h34m 1 12002 14 0Now we’ll need to filter the prefixes of every other peer to allow for only IPv6 routes sized /32 or larger:
route-map IPv6-BILAT-IN permit 100 match ipv6 address prefix-list IPv6-PERMIT-ANY-32 set community 65403:1425 set local-preference 200 ipv6 prefix-list IPv6-PERMIT-ANY-32 seq 5 permit ::/0 le 32Once applied to the peers this will limit the routes installed into the FIB. Install them by adding the route-map to the appropriate peers:
neighbor 2001:db8:0:300e::1 route-map in IPv6-BILAT-IN
SSH@RTR7#sh ipv6 bgp summary
BGP4 Summary
Router ID: 10.6.16.10 Local AS Number: 65403
Confederation Identifier: not configured
Confederation Peers:
Maximum Number of IP ECMP Paths Supported for Load Sharing: 1
Number of Neighbors Configured: 16, UP: 16
Number of Routes Installed: 15297, Uses 1315542 bytes
Number of Routes Advertising to All Neighbors: 50641 (5632 entries), Uses 270336 bytes
Number of Attribute Entries Installed: 26036, Uses 2343240 bytes
Neighbor Address AS# State Time Rt:Accepted Filtered Sent ToSend
2001:db8:1900:b::2
65531 ESTAB 56d 8h52m 14 0 2 0
2001:db8:f000:213a::1
65164 ESTAB 3d19h31m 4187 4535 2 0
2001:db8:0:300e::1
65381 ESTAB 56d 8h35m 5087 6532 2 0
2001:db8:5fff:1::1
65237 ESTAB 149d16h18m 11 0 2 0
2001:db8:1:102::1
65100 ESTAB 24d16h55m 3 0 2 0
2001:db8:f10:1::1 65403 ESTAB 453d12h42m 3 0 5625 0
2001:db8:f10:1::2 65403 ESTAB 101d21h24m 2 0 5625 0
2001:db8:f10:1::3 65403 ESTAB 453d11h29m 1 0 5625 0
2001:db8:f10:1::4 65403 ESTAB 453d11h 8m 1 0 5625 0
2001:db8:f10:1::5 65403 ESTAB 453d12h17m 1 0 5625 0
2001:db8:f10:1::6 65403 ESTAB 453d12h 3m 1 0 5625 0
2001:db8:f10:1::7 65403 ESTAB 453d11h36m 1 0 5625 0
2001:db8:f10:1::8 65403 ESTAB 160d17h52m 5078 0 5625 0
2001:db8:f10:1::9 65403 ESTAB 453d11h 3m 1 0 5625 0
2001:db8:f10:6013::2
65532 ESTAB 15d19h50m 904 3 2 0
2001:db8:f10:6016::2
65527 ESTAB 126d15h29m 1 0 2 0
As you can see, peers on AS65164 and AS65381 are both filtering a large amount of traffic that is smaller than /32. Couple that with the inclusion of a default route and the traffic has a good deal of best path and a default for everything else. Its not exactly the most elegant, but it does solve a problem that folks may be seeing on aging equipment with limited resources.