Getting pretty close to default IPv4 route maximum for 6500/7600 routers.

Blake Hudson blake at
Tue Jun 10 17:04:14 UTC 2014

I haven't seen anyone bring up this point yet, but I feel like I'm 
missing something...

I receive a full BGP table from several providers. They send me ~490k 
*prefixes* each. However, my router shows ~332k *subnets* in the routing 
table. As I understand it, the BGP table contains duplicate information 
(for example a supernet is announced as well as all subnets within that 
supernet) or excess information (prefix is announced as two /17's 
instead of a single /16) and can otherwise be summarized to save space 
in the RIB.

It appears to me that the weekly CIDR report shows similar numbers:

Recent Table History
         Date      Prefixes    CIDR Agg
         30-05-14    502889      283047
         31-05-14    502961      283069
         01-06-14    502836      283134
         02-06-14    502943      283080
         03-06-14    502793      283382
         04-06-14    503177      282897
         05-06-14    503436      283062
         06-06-14    503988      282999

In this case, does the 512k limit of the 6500/7600 refer to the RIB or 
the FIB? And does it even matter since the BGP prefix table can 
automatically be reduced to ~300k routes?


Drew Weaver wrote the following on 5/6/2014 10:39 AM:
> Hi all,
> I am wondering if maybe we should make some kind of concerted effort to remind folks about the IPv4 routing table inching closer and closer to the 512K route mark.
> We are at about 94/95% right now of 512K.
> For most of us, the 512K route mark is arbitrary but for a lot of folks who may still be running 6500/7600 or other routers which are by default configured to crash and burn after 512K routes; it may be a valuable public service.
> Even if you don't have this scenario in your network today; chances are you connect to someone who connects to someone who connects to someone (etc...) that does.
> In case anyone wants to check on a 6500, you can run:  show platform hardware capacity pfc and then look under L3 Forwarding Resources.
> Just something to think about before it becomes a story the community talks about for the next decade.
> -Drew

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