I have a very strange issue SSHing into an Ubuntu server hosted at Amazon Web Services from one IP address.
A few weeks back our ISP made some changes in the building we share with other businesses and as such our IP address changed. No problem, I updated the AWS security groups and thought job done.
Apart from one server, that shares the same security group as server that work fine. The server has a twin, almost identical, in the same location performing the same function (its a web application cluster).
I can SSH into this machine from any location the security group is set to allow EXCEPT the office IP address. The connection times out.
I assumed that the server itself must be blocking the connection but:
- There is no firewall running
- There is no anti brute-force running
- hosts.deny is blank (comments only)
- I see no mention of the login attempt in auth.log
All non-ssh services seem to connect, for example, if I allow pings it will respond to pings as expected.
Can anybody think of anything I have missed here? What else could be preventing this connection?