IPIP tunnel

Tomas Buday (tomas@snt.sk)
Tue, 10 Nov 1998 13:47:21 +0100 (CET)


hi there,

i need som help setting up the IPIP tunnel. actually
i know how to set it up....but there's something i'm
missing i'm sure.

this is how my tunnel works betwwen two machines:

machine 1
---------

ifconfig tunl0 192.168.1.2 pointopoint 15.188.34.122
route add -net 192.168.1.0 tunl0

OK, now i can ping 192.168.1.1 (local IPIP interface)
..and i also send out encapsulated packets.

when pinging 192.168.1.1, tcpdump says:

13:33:56.801988 192.168.1.2 > 192.168.1.1: icmp: echo request (ipip)
13:33:57.801988 192.168.1.2 > 192.168.1.1: icmp: echo request (ipip)
13:33:58.801988 192.168.1.2 > 192.168.1.1: icmp: echo request (ipip)

similarly i set up the other side of tunnel and everything works
fine....i can get connected via the tunnel. works just fine!

BUT:

this has only been for testing....the real job needs to be done
on our server. so i set it up the very same way, but it doesn't work.
first i thought there was something wrong with the kernel so a
recompiled it....even tried the one from the testing machine...still
no success:(

next i disabled all firewalling rules...no success.

i can see encapsulated packets come to the server (using tcpdump)
but it refuses them...does not react at all.

then i tried to ping the the other side from the server....and using
tcpdump again i could NOT see any encapsulated packets!!! so the reason
why the server does not respond, i guess has to do with it not being
able to send out encapsulated packets.

why is that?

*) i have the same kernel on the machines
*) no fw rules
*) same network setup
*) have linux 2.0.35 (rh-5.1)
*) i don't use modules...everything in the vmlinuz
*) i can of course see tunl0 in /proc/net/dev

THANK YOU very much in advance for helping me solve my problem or
just for giving me a clue of what's going on here.

...i'm not subscribed to LKML, please send replies directly back to me.
THANK YOU!

tomas buday

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