[c-nsp] Unicast storms

[Gert Doering]

Hi,

On Thu, Jul 05, 2007 at 04:05:24PM +0100, Stephen Wilcox wrote:
> your LAN would need to be very large or very unusual for you to see this as a problem

Don't be so quick with this assessment.

We have (some time in the past) had our routers flood about 20 Mbit/s
of NNTP traffic to one of our DNS servers, which had only a 10Mbit/s-Link.

Obviously this wasn't so good for service levels...

(The solution was: "make sure that all switches know the MAC address of
the NNTP server" - solved in our case by running rwhod and doing periodic
broadcasts).

> for most networks MAC learning will occur quickly as most stations
> send at least *some* sort of data onto the LAN from time to time
> so that the switches will learn where they are

As soon as you have multiple switches and multiple routers, chances
are high that some switches only very very rarely see packets from 
machines connected to other switches (has been explained in this thread
already!), and thus, these switches have to unicast-flood packets *to*
the machines in question.

gert
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de