Conecting via SSH ubuntu to Cisco IOS, XE

[f4cruz]

I'm try to connect via ssh from my server ububtu to 2 routers:

R1 - CiscoIOS , R2 -IOS-XE

I edited the  /etc/ssh/ssh_config file and add:

KexAlgorithms diffie-hellman-group1-sha1 ( for IOS work very well but not for XE )

but if I add:

KexAlgorithms diffie-hellman-group14-sha1 ( for XE work very well but not for IOS )

there area any way to configure both in the /etc/ssh/ssh_config file?

thanks.

PD. this is the error for IOS-XE:

Unable to negotiate with 192.168.80.50 port 22: no matching key exchange method found. Their offer:
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group14-sha1

[Flavio Miranda · Accepted solution]

@f4cruz 

 There is a similar discussion here with a solution

https://askubuntu.com/questions/1279881/ubuntu-20-04-unable-to-ssh-to-cisco-ios

[Harold Ritter]

Hi @f4cruz ,

You can specify both separated by a comma as follow:

KexAlgorithms diffie-hellman-group1-sha1, diffie-hellman-group14-sha1

You can check the configured values as follow:

test@test$ ssh -Q KexAlgorithms

diffie-hellman-group1-sha1

diffie-hellman-group14-sha1

diffie-hellman-group14-sha256

diffie-hellman-group16-sha512

diffie-hellman-group18-sha512

diffie-hellman-group-exchange-sha1

diffie-hellman-group-exchange-sha256

ecdh-sha2-nistp256

ecdh-sha2-nistp384

ecdh-sha2-nistp521

curve25519-sha256

curve25519-sha256@libssh.org

sntrup4591761x25519-sha512@tinyssh.org

Regards,

[f4cruz]

Hello Harold

I got this after add this line:

ssh cisco@192.168.80.50  
/etc/ssh/ssh_config line 58: keyword kexalgorithms extra arguments at end of line
/etc/ssh/ssh_config: terminating, 1 bad configuration options

[Harold Ritter]

Hi @f4cruz ,

Yes, I had an extra blank in there. Glad to see you fixed it.

Regards,

[f4cruz]

this worked for me, thank you guys.

KexAlgorithms diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1