Getting pretty close to default IPv4 route maximum for 6500/7600 routers.
blake at ispn.net
Tue Jun 10 18:36:09 UTC 2014
joel jaeggli wrote the following on 6/10/2014 1:10 PM:
> On 6/10/14, 10:39 AM, Blake Hudson wrote:
>> Łukasz Bromirski wrote the following on 6/10/2014 12:15 PM:
>>> Hi Blake,
>>> On 10 Jun 2014, at 19:04, Blake Hudson <blake at ispn.net> wrote:
>>>> 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?
>>> Te 512k limit refers to FIB in the B/C (base) versions of 6500/7600
>>> Supervisors and DFCs (for line cards). BXL/CXL versions have FIB for
>>> 1M IPv4 prefixes.
>>> You can find more information here:
>>> And yes, you’re right - no matter how many neighbors you have, the FIB
>>> will only contain best paths, so it will be closer to 500k entries in
>>> total rather than N times number of neighbours.
>> Please correct me if I'm wrong, but if the BGP table contains ~500k
>> prefixes, which are then summarized into ~300k routes (RIB),
> Unlikely, just because prefixes could be cidr aggregated doesn't mean
> they are. the more specifics exist for a reason, in the case of
> deaggrates with no covering anouncement, well not much you're doing with
> your rib should be the sum of all received routes that you did not filter.
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
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
>> and the FIB
>> contains only the "best path" entries from the RIB, wouldn't the FIB be
>> at or below 300k?
> a live example of rib size from a router with two transit providers.
> bird> show route count
> 979842 of 979842 routes for 490932 networks
> a live example of rib size from a router with one ibgp peer with addpath
> and three upstream transit providers
> bird> show route count
> 1471242 of 1471242 routes for 491977 networks
The RIB counts and memory used by the RIB seem to be nearly identical
between a Cisco router with 3 full BGP feeds and another with 1 BGP
feed. The differences seem to lie in the memory used by BGP for prefix
tracking. If your router has multiple routing tables, or your installing
multiple routes for the same prefix in the RIB, then I can understand
why your RIB will be larger. These are nice features, but certainly not
a requirement for everyone.
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