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⇤ ← Revision 1 as of 2018-05-08 22:54:59
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| ... | * 2018 Ubuntu 14.04 (old) could not connect to another machine, doing a tcpdump found {{{ 22:31:17.504887 IP 10.128.155.77.ssh > 10.128.145.23.46488: Flags [.], seq 45:1493, ack 2013, win 257, options [nop,nop,TS val 2677742 ecr 60427352], length 1448 22:31:17.505381 IP 172.16.6.2 > 10.128.155.77: ICMP 10.128.145.23 unreachable - need to frag (mtu 1436), length 556 }}} * Ubuntu was ignoring the ICMP and thus the ssh just hanged. * Fix1 - static route with mtu {{{ # ip route add 10.118.145.0/27 via 10.118.155.65 mtu 1400 }}} * Root Cause - uRPF explained here [[http://mellowd.co.uk/ccie/?p=5662]] a security feature. |
MTU
- Maximum Transmission Unit - of packets, normally for ethernet 1500
Links: linux/PacketOffloadingMtu
- 2018 Ubuntu 14.04 (old) could not connect to another machine, doing a tcpdump found
22:31:17.504887 IP 10.128.155.77.ssh > 10.128.145.23.46488: Flags [.], seq 45:1493, ack 2013, win 257, options [nop,nop,TS val 2677742 ecr 60427352], length 1448 22:31:17.505381 IP 172.16.6.2 > 10.128.155.77: ICMP 10.128.145.23 unreachable - need to frag (mtu 1436), length 556
- Ubuntu was ignoring the ICMP and thus the ssh just hanged.
Fix1 - static route with mtu
# ip route add 10.118.145.0/27 via 10.118.155.65 mtu 1400
Root Cause - uRPF explained here http://mellowd.co.uk/ccie/?p=5662 a security feature.