network problem due to mtu value

ssh problem

Posted by JXLIU on August 28, 2022

In the following, I divide the problem finding and problem solving into several stages.


stage 1. hanging on when accessing nfs

nfs can be exported in the nfs server and can be mounted in the nfs client.[]

But it will hang on when connectting the client through ssh or accessing the nfs.

I still can excute command through the following method

ssh heq "ls /"

stage 2. exporting and mounting nfs through normal network instead of ib network

If nfs is exported in the server and mounted in the client through normal network instead of infiniband network, ssh connection is successful and nfs is available.

So, there is something wrong about infiniband network.

stage 3. ping and ssh through ib network

next, it was found that ping works well through ib network. but ssh always fails through ib network.

Then the following command is used to find the root of the problem

ping -M do -s 100 ibio01
ping -M do -s 200 ibio01
ping -M do -s 300 ibio01
ping -M do -s 400 ibio01

it means the value of mtu of infiniband switch is too small.


问题:ssh connection stop at "debug1: SSH2_MSG_KEXINIT sent" 解决方案: ib 网卡的 mtu 值需要一致(destination 的不能太大)