[vpnc-devel] ICMP fragmentation needed

["Garamszegi Károly (Ateo)"]

Hi,

the problem is it works only if I set the MTU to 900 _manually_. I think this is not the way it should work. 
That would mean, on any network I connect to, I would have to manually figure out, what is the maximal packet size,
and set it by hand. Clearly, this is not the way, how it should work.
In my humble opinion, the application shall reduce the packet size on getting the ICMP fragmentation needed packet.

Please correct me, if I am wrong.

Regards,

Karoly


|Hello,
|
|I don't get the problem if everything is fine. You just have to put the mtu
|to 900...
|
|Regards,
|Bernd
|
|2009/3/26 "Garamszegi Károly (Ateo)" <kgaramszegi at ateo.hu <https://lists.unix-ag.uni-kl.de/mailman/listinfo/vpnc-devel>>
|
>/  Dear All,
/>/
/>/ I have a problem with vpnc (0.5.3) on ubuntu (8.10). I start the VPN
/>/ connection to Cisco VPN router (A.B.C.D)
/>/
/>/ root at moon <https://lists.unix-ag.uni-kl.de/mailman/listinfo/vpnc-devel>:~# tcpdump host A.B.C.D or icmp  -n -v
/>/ tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96
/>/ bytes
/>/ 12:27:24.295628 IP (tos 0x0, ttl 64, id 40755, offset 0, flags [DF], proto
/>/ UDP (17), length 1296) 158.67.184.47.500 > A.B.C.D.500: isakmp 1.0 msgid :
/>/ phase 1 I agg: [|sa]
/>/ 12:27:24.296316 IP (tos 0x0, ttl 72, id 18832, offset 0, flags [none],
/>/ proto ICMP (1), length 56) MyUpstreamRouter > 158.67.184.47: ICMP A.B.C.D
/>/ unreachable - need to frag (mtu 900), length 36
/>/     IP (tos 0x0, ttl 63, id 40755, offset 0, flags [DF], proto UDP (17),
/>/ length 1296) 158.67.184.47.500 > A.B.C.D.500: [|isakmp]
/>/
/>/
/>/ My upstream router sends an ICMP Fragmentation needed, but the application
/>/ does not send a packet with a smaller packet size. If I manually set the
/>/ interface MTU to 900 byte, everything works fine. Would you please advise?
/>/
/>/
/>/ Regards,
/>/
/>/  --
/>/ Garamszegi Károly
/>/
/>/
/

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