Just tried to connect to a couple of old Cisco Switches from Ubuntu 22.04
1 2 3 4 5 6 | lsb_release -aNo LSB modules are available.Distributor ID: UbuntuDescription: Ubuntu 22.04.2 LTSRelease: 22.04Codename: jammy |
The Problem - (I think this is a WS-C2960X)
1 2 3 | ssh 10.11.12.13# outputUnable to negotiate with 10.11.12.13 port 22: no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 |
The Resolution
1 | ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 -oHostkeyAlgorithms=+ssh-rsa 10.11.12.13 |
Step by Step Example of Fixing the Problem when connecting to a WS-C2960G-48TC-L
This shows the process of adding command line options based on the "Their offer:" reply from the switch until you finally get a login prompt
1 2 3 | ssh 10.11.12.14# outputUnable to negotiate with 10.11.12.14 port 22: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 |
So add KexAlgorithms
1 2 3 | ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 10.11.12.14# outputUnable to negotiate with 10.11.12.14 port 22: no matching host key type found. Their offer: ssh-rsa |
Then add HostkeyAlgorithms
1 2 3 | ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 -oHostkeyAlgorithms=+ssh-rsa 10.11.12.14# outputUnable to negotiate with 10.11.12.14 port 22: no matching cipher found. Their offer: aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc |
Then add Cipher (-c) and finally we have a login prompt
1 2 3 | ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 -oHostkeyAlgorithms=+ssh-rsa -c aes128-cbc 10.11.12.14# output(jamesm@10.11.12.14) Password: |
Sometimes things are so old you have to go Old-Old School
Sometimes you try to connect with ssh and you get
1 2 3 | ssh 10.11.12.25# ssh: connect to host 10.11.12.25 port 22: Connection refused |
So then you might need to install a telnet client
1 | sudo apt-get install telnet |
Try again with telnet
1 2 3 4 5 6 7 8 9 10 | telnet 10.11.12.25# outputTrying 10.11.12.25...Connected to 10.11.12.25.Escape character is '^]'.User Access VerificationUsername: |
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