From: "pupilla@libero.it" <pupilla@libero.it>
To: <luky-37@hotmail.com>, <netdev@vger.kernel.org>
Subject: R: RE: per route MTU settings
Date: Mon, 14 Jan 2013 09:51:53 +0100 (CET) [thread overview]
Message-ID: <30645799.1106291358153513079.JavaMail.defaultUser@defaultHost> (raw)
luky-37@hotmail.com wrote:
>I guess 10.81.104.1 has a 576B MTU route/interface towards
>10.81.105.109,
no, 10.81.104.1 is only a L3 switch.
>Running from both hosts pings with:
>-s 548
>-s 549
>-s 1422
>-s 1423
>
>and then analyzing the results will probably give us a better
>idea of what actually happens.
here is the results:
root@10.81.104.254:~# ip route add 10.81.105.121/32 via 10.81.104.1 mtu lock
1450
root@10.81.104.254:~# ip r s | grep 10.81 | grep eth2
10.81.104.0/24 dev eth2 proto kernel scope link src 10.81.104.254
10.81.104.0/21 via 10.81.104.1 dev eth2
10.81.105.121 via 10.81.104.1 dev eth2 mtu lock 1450
root@10.81.104.254:~# ip route flush cache
root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 548
PING 10.81.105.121 (10.81.105.121) 548(576) bytes of data.
556 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.476 ms
556 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.448 ms
556 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.515 ms
root@10.81.104.254:~# ip route flush cache
root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 549
PING 10.81.105.121 (10.81.105.121) 549(577) bytes of data.
557 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.386 ms
557 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.525 ms
557 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.447 ms
root@10.81.104.254:~# ip route flush cache
root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 1422
PING 10.81.105.121 (10.81.105.121) 1422(1450) bytes of data.
1430 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.724 ms
1430 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.785 ms
1430 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=1.95 ms
root@10.81.104.254:~# ip route flush cache
root@10.81.104.254:~# ping -M do 10.81.105.121 -c 4 -s 1423
PING 10.81.105.121 (10.81.105.121) 1423(1451) bytes of data.
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450)
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450)
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 1450)
root@10.81.104.126:~# ip r s
default via 10.81.104.254 dev eth0 metric 1
10.81.104.0/24 dev eth0 proto kernel scope link src 10.81.104.126
127.0.0.0/8 dev lo scope link
root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 548
PING 10.81.105.121 (10.81.105.121) 548(576) bytes of data.
556 bytes from 10.81.105.121: icmp_req=1 ttl=127 time=0.352 ms
556 bytes from 10.81.105.121: icmp_req=2 ttl=127 time=0.372 ms
556 bytes from 10.81.105.121: icmp_req=3 ttl=127 time=0.368 ms
root@10.81.104.126:~# ip route flush cache
root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 549
PING 10.81.105.121 (10.81.105.121) 549(577) bytes of data.
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 576)
I don't undestand why 10.81.104.254 here, is reporting
that the mtu is 576 instead of 1450
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
root@10.81.104.126:~# ip route flush cache
root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 1422
PING 10.81.105.121 (10.81.105.121) 1422(1450) bytes of data.
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 576)
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
root@10.81.104.126:~# ip route flush cache
root@10.81.104.126:~# ping -M do 10.81.105.121 -c 4 -s 1423
PING 10.81.105.121 (10.81.105.121) 1423(1451) bytes of data.
>From 10.81.104.254 icmp_seq=1 Frag needed and DF set (mtu = 576)
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
>From 10.81.104.126 icmp_seq=2 Frag needed and DF set (mtu = 576)
reply other threads:[~2013-01-14 8:51 UTC|newest]
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