R: RE: per route MTU settings
Subsystems (2)
Quoted 2 lines · [email protected] 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.
Quoted 8 lines
Running from both hosts pings with:
(quoted diff) +0
-4-s 548 -s 549 -s 1422 -s 1423and then analyzing the results will probably give us a better idea of what actually happens.
here is the results:
[email protected]:~# ip route add 10.81.105.121/32 via 10.81.104.1 mtu lock 1450 [email protected]:~# 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 [email protected]:~# ip route flush cache [email protected]:~# 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
[email protected]:~# ip route flush cache [email protected]:~# 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
[email protected]:~# ip route flush cache [email protected]:~# 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
[email protected]:~# ip route flush cache [email protected]:~# 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.
Quoted 3 lines
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)
[email protected]:~# 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
[email protected]:~# 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
[email protected]:~# ip route flush cache [email protected]:~# 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.
Quoted 1 line
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
Quoted 2 lines
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)
[email protected]:~# ip route flush cache [email protected]:~# 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.
Quoted 3 lines
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)
[email protected]:~# ip route flush cache [email protected]:~# 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.
Quoted 3 lines
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)