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I am trying to retrieve the ssh key from a Cisco Switch and get the following output:

[root@localhost] ssh-keyscan -T15 172.20.10.11
# 172.20.10.11:22 SSH-2.0-Cisco-1.25
# 172.20.10.11:22 SSH-2.0-Cisco-1.25
# 172.20.10.11:22 SSH-2.0-Cisco-1.25

I've ran the same command on a Cisco Router and it returns a SSH key.

What could be the issue?

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It usually means that the client and server did not support any common key exchange algorithms. For example, the server might be old enough that it only offers "diffie-hellman-group1-sha1" which modern OpenSSH disables by default – 'ssh' allows re-enabling it through config, but 'ssh-keyscan' lacks that option.

(Although 'key exchange' mainly refers to establishing a shared key for encryption, e.g. through the DH algorithm, the server's host key is sent during the same process to authenticate the key exchange – there is no separate "here is my host key" message.)

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