<Keepalives are temporarily in throttle due to closed TCP window>

Brian Dickson Brian.Dickson at concertia.com
Wed Sep 16 20:03:42 UTC 2009

RAS wrote:

[ lots of good stuff elided for brevity ]

> c) lower the mtu on the ds3 interface to 1500.

This will have another benefit, if it is done to all such interfaces on the two devices.
(Where by "all such interfaces", I mean "everything with set-able MTU > 1500".)

Configuring one common MTU size on the interfaces, means the buffer pool on the box will switch from several pools of varying sizes, to one pool.
The number of buffers per pool get pro-rated by speed * buffer size, so high-speed, high-MTU interfaces get a gigantic chunk of buffer space.

Once you reduce things to one pool, you significantly reduce the likelihood of buffer starvation.

Note that the discussion on benefits to buffers is old info, and may even be moot these days, but buffers are fundamental enough that I doubt it.

However, the original problem, iBGP not working, will definitely be resolved by this.

Note also, changing this often won't take effect until a reboot, and/or may result in buffer re-carving with an attendant "hit" of up to 30 seconds of no forwarding packets (!!). You've been warned...

In other words, plan this carefully, and make sure you have remote hands available or are on site. This qualifies as "deep voodoo". ;-)


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