Getting pretty close to default IPv4 route maximum for 6500/7600 routers.
blake at ispn.net
Wed Jun 11 13:53:02 UTC 2014
Matthew Petach wrote the following on 6/10/2014 7:03 PM:
> On the couple Cisco platforms I have available with full tables, Cisco
> summarizes BGP by default. Since this thread is talking about Cisco
> gear, I think it's more topical than results from BIRD.
> One example from a non-transit AS:
> ASR#sh ip route sum
> IP routing table name is default (0x0)
> IP routing table maximum-paths is 32
> Route Source Networks Subnets Replicates Overhead
> Memory (bytes)
> connected 0 10 0 600 1800
> static 1 2 0 180 540
> application 0 0 0 0 0
> bgp xxxxx 164817 330796 0 29736780 89210340
> External: 495613 Internal: 0 Local: 0
> internal 5799 20123680
> Total 170617 330808 0 29737560 109336360
> I'm not sure you're reading that correctly.
> 164817+330796 = 495613
> That is, the BGP routing table size is the
> union of the "Networks" and the "Subnets";
> it's not magically doing any summarization
> for you.
Thank you Matt for directly addressing my question. My interpretation,
which seems likely incorrect, was that smaller announcements could be
discarded if there was a covering prefix (that otherwise matched the
same AS path and other BGP metrics) and that many smaller prefix
announcements could be bundled (again, assuming that all BGP metrics
were the same between the prefixes). The numbers I was seeing in my
routers for subnets coincided closely with the cidr-report's
summzarization numbers http://www.cidr-report.org/as2.0/aggr.html, and I
assumed the two used the same logic (not magic) to calculate how to
reduce routes without losing any routing functionality. Your explanation
that I was simply interpreting the numbers incorrectly seems the most
logical now that I look again.
More information about the NANOG