BGP peering strategies for smaller routers

Łukasz Bromirski lukasz at bromirski.net
Tue May 3 21:13:11 UTC 2016


> On 03 May 2016, at 22:31, William Herrin <bill at herrin.us> wrote:
> 
> On Tue, May 3, 2016 at 3:50 PM, Gustav Ulander
> <gustav.ulander at telecomputing.se> wrote:
>> Yes I can confirm that we also had the issue with the asr1001s.
>> For us the router was fine until we upgraded it. When
>> we rebooted it after the upgrade it ran out of memory
>> when populating 2 full feeds.
>> When we contacted TAC they confirmed that indeed
>> it was a memory problem and that we would need to
>> add more memory to the box.
> 
> Hi Gustav,
> 
> IMO, you should not accept that answer from the TAC. An IOS release
> that crashes with two 600k BGP feeds in 4 gigs of RAM is badly
> defective.

Not necessarily.

In essence, your physical memory gets halved in two after
router boots up, then it may be further halved if you’re
using features like SSO. So, with 4GB RAM config and with
SSO running, you may be left with around 600-650MB free after
boot and with IOS-XE loaded, and then all the features kick
in. Including your BGP feeds that need around 300MB of memory
just to store the tables, then there’s CEF RAM representation,
and so on.

Here’s a good WP w/r to memory usage & architecture on ASR 1k:
http://www.cisco.com/c/en/us/support/docs/routers/asr-1000-series-aggregation-services-routers/116777-technote-product-00.html

It actually contains the same recommendation given by TAC -
with recent/current code if you want to run full tables with
BGP, get 8GB of RAM on ASR 1k. In the 3.10-3.12S era I believe
it was still possible to fit (without the SSO) full tables
in RAM and be fine. 

As Nick just responded, it’s faster to source the RAM or modify
the config to cut down on number of BGP prefixes rather than
ping back and forth here discussing all the possibilities.

-- 
Łukasz Bromirski
CCIE R&S/SP #15929, CCDE #2012::17, PGP Key ID: 0xFD077F6A



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