[126520] in North American Network Operators' Group
Re: BGP and convergence time
daemon@ATHENA.MIT.EDU (Joel Jaeggli)
Thu May 20 00:34:33 2010
Date: Wed, 19 May 2010 21:34:05 -0700
From: Joel Jaeggli <joelja@bogus.com>
To: surfer@mauigateway.com
In-Reply-To: <20100512144100.4C012F09@resin12.mta.everyone.net>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 05/12/2010 02:41 PM, Scott Weeks wrote:
>
>
> --- danny@tcb.net wrote: From: Danny McPherson <danny@tcb.net> On May
> 12, 2010, at 9:40 AM, Jay Nakamura wrote:
>
>> I just tested this and, yes, with Cisco to Cisco, changing the
>> setting won't reset the connection but you have to reset the
>> connection to have the value take effect. I need to look up what
>> happens when two sides are set to different values and which one
>> takes precedent.
>
> : The holdtime isn't technically negotiated, both sides convey their
> : value in the open message and the lower of the two is used by both
> : BGP speakers.
>
> This isn't a negotiation?
>
>
> : IIRC, neither J or C reset the session with the timer change, but
> the : new holdtimer expiry value doesn't take effect until then.
>
> We use Alcatel 7750s. Damn thing just resets the session; no
> warning, no nothing. :-(
>
>
>
> : One other thing to note is that by default, keepalive intervals in
> : those implementations are {holdtime/3}. Normally, if you're
> setting : holdtime to something really lower (e.g., 10 seconds) you
> might want : to increase the frequency of keepalives such that the
> probability of : getting one through in times of instability rise.
> In particular, : congestion incurred outside of BGP, as update
> messages themselves : will serve as implicit keepalives, and with the
> amount of churn in BGP, : empty updates (keepalives) are rare for
> most speakers with a global BGP : view.
>
> I have been looking for info on the negative impact on a router by
> increasing the keepalive frequency to a high rate. I'm sure it's
> minimal for a few BGP peers, but I could imagine with a lot of peers
> it's a non-zero impact.
with a keep alive interval of 10 seconds you can expect to get 10pps
from a 100 peers. the keepalive message is 19bytes
That doesn't seem particularly hurtful even by the standards of 5 year
old control plane processors.
> scott
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