Recently
I have updated one of the server to CentOS 7. It have access to
several network. With the previous CentOS version, it had SSH access
to those networks. But with the server upgrade the server was not
able to access via SSH.
To
troubleshoot the issue I have run ssh with the the verbose mode.
#ssh
-vvv <Remote server IP> -l <user name>
Then
session got stuck in SSH2_MSG_KEX_DH_GEX_GROUP
message.
If
I briefly explain the network setup, there is a intermediate firewall
which is controlling all the network traffic between those VLANS. I
found by googling that it's something related to the packet
fragmentation.
By
default Network card MTU ( Maximum transfer unit ) is 1500. Then I
have run the below command
to change the MTU of the network card.
#ifconfig
<network_device_name> mtu 576
( You can try with different MTU 1000, 1472, or 567 )
Then
I tried to ssh from the other network, It worked. If you want more
details then you can refer the below link.
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