FW: TNT issues "workaround"

Sat Aug 23 22:42:49 UTC 2003

On Sat, 23 Aug 2003, Ross Chandler wrote:

> > I seem to be having the same or similar problems with my Cisco boxes
> > also , they either reboot or the pris hang , users get busy's but no
> > one is logged in at all , when I do a show isdn status it shows b
> > channels in use but no one on, the only way to fix is reboot the box ,
> > and it seems to be timed , everyday at 1400 and 2200 hours , since
> > Monday anybody body heard of ciscos acting funny this week?
> 
> Perhaps your fast switching route cache is filling up memory. If you're
> willing to risk it enable CEF on all interfaces.

Some of the older cisco access-servers don't even support CEF.  The cisco
failures seem to be memory starvation/fragmentation issues caused by out
of control route-cache growth caused by the nachi worm's attempt to ping
so many different hosts so quickly while looking for systems to spread to.

You can work around the issue by:

a) using policy routing to pass all dialup traffic through a route-map 
that sends 92 byte echo/echo-reply packets to null0.

b) blocking all echo/echo-reply coming in from dial-up users (i.e. apply 
an input acl to your virtual-template and/or group-async interfaces).

c) disabling route caching on the egress interface of the access server.

I'm doing a mix of a (on the access-servers that this works on) and b 
where a doesn't work...and tested c this morning and found it appears to 
work.

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 Jon Lewis *jlewis at lewis.org*|  I route
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