Messages in this thread | | | From | Herbert Xu <> | Subject | Re: XFRM / DF Flag / Fragmentation Needed | Date | Wed, 17 Nov 2004 12:36:18 +1100 |
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Thomas DuBuisson <dubu0874@uidaho.edu> wrote: > > After A establishes an SSH connection with C and tries to transfer the > patches the size of a packet from A destined for C is quickly reaches 1500 > while the MTU > to A is ~1400. At this point A sends an ICMP 'Fragmentation Needed' > packet to its self (see xfrm_output.c xfrm4_tunnel_check_size(...)). It > seems this packet is never acted on - it just disappears into the > loopback interface. The proper mtu trial/error process never takes > place.
There is a known problem in xfrm4_tunnel_check_size if your underlying path MTU is a multiple of 8. So if your path MTU is 1480, you'll need to lower it to 1476 before it will work.
You can query the path MTU using "ip r g <remote-gateway>". If it is a multiple of 8, you can change it by doing
ip r a <remote-gateway> ... mtu <current-mtu - 4> -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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