Getting logs as "SSH2 10: Invalid modulus length" on Cisco 2951

[tilekar.shrikant]

Hi,

I am getting below logs on my Cisco router(CISCO2951) having IOS(:c2951-universalk9-mz.SPA.150-1.M4.bin) 

*May 31 02:48:56.579: SSH2 8:  Invalid modulus length
*May 31 02:58:56.808: SSH2 7:  Invalid modulus length
*May 31 03:08:56.284: SSH2 2:  Invalid modulus length
*May 31 03:18:46.224: SSH2 4:  Invalid modulus length
*May 31 03:28:17.079: SSH2 6:  Invalid modulus length
*May 31 03:38:47.245: SSH2 15:  Invalid modulus length
*May 31 03:48:49.257: SSH2 5:  Invalid modulus length
*May 31 03:58:13.036: SSH2 7:  Invalid modulus length
*May 31 04:07:34.487: SSH2 8:  Invalid modulus length
*May 31 04:16:54.849: SSH2 10:  Invalid modulus length

What is the exact issue and solution?

[Milos Megis]

Hi
what is length of your modulus, which you entered when you type command "crypto key generate rsa" ?

For SSH2 it must be at least 768 bits (I think).

[tilekar.shrikant]

Hi,

Length  is 1024 bits.

[Milos Megis]

It should be enough for SSH2.

I don´t know, maybe try manual from above link from Karsten.

[Karsten Iwen]

I wrote a document on how to configure SSH in IOS. It should work after setting it up correctly: https://supportforums.cisco.com/document/12338141/guide-better-ssh-security