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

Blake Hudson blake at
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> 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
> those.
> 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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