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Re: Extreme + Nachi = ipfdb overflow

  • From: Richard A Steenbergen
  • Date: Mon Aug 25 16:10:02 2003

On Mon, Aug 25, 2003 at 03:38:52PM -0400, Joshua Coombs wrote:
> After battling Nachi and it's flood of icmp traffic, I've discovered
> that it's not the Cisco gear that gets hit hard by it, it was the
> Extreme gear.  Nachi generates enough 'random' traffic to flood and
> subsequently thrash the ip forwarding DB on the Summit 1i we were using
> so badly as to drop it from gigabit capible to barely eeking out
> 6mb/sec.  Before I redeploy the switch, I need to find a way to keep the
> ipfdb from flodding while allowing it to be the primary carrier of
> traffic.  ACLs blocking ICMP on the Extreme act too late, by the time
> the cpu sees the packet to drop it, it's already horned its way into the
> ipfdb.  Does anyone have any suggestions on ways to allow the switch to
> participate as an L3 router while minimizing the chances of a worm
> taking it out so easily again?

This affects most layer 3 switches, including Extreme, Foundry, and anyone
else who still can't figure out how to pre-generated a FIB instead of a 
Fast Cache style system. 

It amazes me that people still have not learned this lesson. How old is
CEF now? Then again, I suppose most of these boxes are being marketed to
Enterprises anyways. As long as there is a label that says "60Gbps", the
box looks good, and it's relatively cheap, how many of their customers are
really going to notice the first packet performance of 6Mbps before they
buy, right?

At least some of the other vendors have workarounds (lame as they might be
*coughnetaggcough*), or newer supervisors with FIBs, but I'm not aware of
anything you can do to make an L3 Barney Switch behave well under a random
dest flood.

Richard A Steenbergen <>
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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