[4669] in RedHat Linux List
Re: tcpdump
daemon@ATHENA.MIT.EDU (Stephen Zedalis)
Sat Nov 16 09:25:52 1996
Date: Sat, 16 Nov 1996 09:24:18 -0500 (EST)
From: Stephen Zedalis <tintype@zedalis.com>
To: "David L. Martin" <dlmarti@pluto.njcc.com>
cc: Redhat <redhat-list@redhat.com>
In-Reply-To: <Pine.LNX.3.94.961115202609.23416A-100000@localhost>
Resent-From: redhat-list@redhat.com
Reply-To: redhat-list@redhat.com
On Fri, 15 Nov 1996, David L. Martin wrote:
> While trying to debug some problems with an nntp connection I used
> tcpdump and found this error occuring all the time:
>
> 21:19:34.137096 termserv2.njcc.com.route > ts2-60.njcc.com.route: rip-resp
> 14: ts2-54.njcc.com(1)[|rip]
> 21:19:34.137422 ts2-60.njcc.com > termserv2.njcc.com: icmp: ts2-60.njcc.com
> udp port route unreachable
To understand this you need a good grounding in basic tcp/ip protocols.
There is a plethora of books out there that will give you the basics.
What is documented from tcpdump above is the header information for two
packets. The first packet is being sent from your terminal server to a
dialup port. It is broadcasting a Routing Information Protocol response
to the dialup machine. Apparently you have this dialup connection set
to Broadcast-Listen for routing. This could be set in your terminal
server or in RADIUS. What is coming back is that either a filter is setup
to prevent the rip packet from coming back or more probably it simply
means that the dialup machine does not understand RIP. By default, you
probably don't need the majority of your dialin ports set for
Broadcast-Listen. Windoze and Mac machines by default don't know what to
do with a routing protocol packet and you really only want to be sharing
routing information with networks that need it. If you had a business
network connected to the dialup and you wanted routing updates to go
to/from that system to yours then you would Broadcast and/or Listen
RIP to them. Leaving Broadcast-Listen on, can also defeat the other guys
timeout features. Your terminal server probably doesn't count RIP
broadcasts in its idle timeout, but since the other machine doesn't know
not to count RIP, if it had an idle timeout, it may not work.
--
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