Saturday 17 January 2015

ssh hangs at SSH2_MSG_KEX_DH_GEX_GROUP trying to connect to servers behind Cisco firewall

Today I was unable to ssh to some CentOS servers behind a Cisco firewall. I was connected using AnyConnect. When I ran ssh with -v, it showed me that it stopped at expecting SSH2_MSG_KEX_DH_GEX_GROUP.

A search on the Internet turned up this article: Natty Narwhal: Problems connecting to servers behind (Cisco) firewalls using ssh. Shortening the Cipher and MAC list as suggested solved the problem. Apparently due to overflowing some packet size limit somewhere. I'll leave it to the experts to work out what it is about Cisco and ssh.

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