BGP peering strategies for smaller routers

William Herrin bill at
Tue May 3 21:53:37 UTC 2016

On Tue, May 3, 2016 at 5:13 PM, Łukasz Bromirski <lukasz at> wrote:
> On 03 May 2016, at 22:31, William Herrin <bill at> wrote:
>> 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:

Hi Łukasz,

You make some great points and that's an excellent document.

> 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.

I respectfully disagree. Sourcing more ram won't fix the next bit of
sloppiness with the software. Or the one after that. Once the manager
of that team starts to accept poor code quality, the only thing with a
chance of fixing it is strong customer push-back.

And it is poor code quality. Even slicing and dicing the ram in odd
ways, there's just no excuse for an order-of-magnitude increase in ram
required to run the same algorithms on the same data.

Bill Herrin

William Herrin ................ herrin at  bill at
Owner, Dirtside Systems ......... Web: <>

More information about the NANOG mailing list