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List:       lartc
Subject:    [LARTC] vtun - mtu problem
From:       Robert Penz <robert.penz () outertech ! com>
Date:       2002-09-29 19:36:31
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Hi!

I want to to that

local network  ---eth0--- tunnel entry point  ---- tunnel exit point.
(windows and linux pcs) 

I'm using vtun and I'm masquerating on both tunnel machines, my problem is now 
that a ping works also small packets but if the packet gets bigger I get that 
with tcpdump on my tunnel exit point.

tcpdump -n -i eth0 host heise.de

21:03:32.595835 194.242.45.xxx > 193.99.144.71: icmp: 10.3.0.2 unreachable - 
need to frag (mtu 1450) [tos 0xc0]
21:03:38.794269 193.99.144.71.80 > 194.242.45.xxx.32819: R 
1387534372:1387534372(0) ack 3349554176 win 0

here the setup of my tunnel entry point:

eth0      Link encap:Ethernet  HWaddr 00:00:CB:59:EE:85
          inet addr:10.149.xx.xx  Bcast:10.149.xx.255  Mask:255.255.240.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

tun0      Link encap:Point-to-Point Protocol
          inet addr:10.3.0.2  P-t-P:10.3.0.1  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1450  Metric:1


I did a little searching on the internet, and the only stuff I found was from 
2000, where something simlular happend, and the answer was to set the clients 
to mtu 1450, is that the still the only way. (didn't try it sofar) 

but what I don't understand, that the mtu is always 1450 .... so why is that 
only a problem with my setup?


- -- 
Regards,
Robert
- ----------------
Robert Penz
robert.penz AT outertech.com
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