BGP prefix filter list

Blake Hudson blake at
Wed May 22 13:14:46 UTC 2019

adamv0025 at wrote on 5/22/2019 3:23 AM:
>> From: NANOG <nanog-bounces at> On Behalf Of Blake Hudson
>> Sent: Monday, May 20, 2019 4:35 PM
>> As I recall reading about one vendor's platform (the ASR9k
>> perhaps?) and its TCAM organization process, it stored /32 routes in a
>> dedicated area for faster lookups and did the same for /24 routes.
> Yes that was true for the first generation (trident based) line-cards and is no longer the case anymore.
> adam
Thanks Adam! For the life of me I could not remember where I read that 
information or what platform it applied to. I do recall it being a very 
transparent view into TCAM organization and I appreciated the insight. 
It was also a good reminder that it pays to understand your platform as 
I had previously (naively) thought that a 1M capacity FIB could hold 1M 
entries with any mask size, whether those be 1M /32 entries (a BRAS with 
1M PPP/BNG subscribers) or 1M /24 or bigger entries (a BGP edge router). 
This was obviously not the case on that platform.

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