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Today a customer contacted me because he has upgraded his MacBook to MacOS X Sierra and since then, when trying to access a switch via SSH he got the message

Unable to negotiate with 10.XX.XX.XX port 22: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1

The switch is a Cisco 2960S running IOS 12.2(55)SE7 (C2960S-UNIVERSALK9-M)

I looked at the command reference guide for this version, but was unable to find any command to configure SSH ciphers. (we can only configure SSH version 1 / 2 or both)

Is it possible with this version?

P.S. Yes I'm aware that he should use RSA key authentication, and upgrade the IOS version, I recommended it but this will need some testing and change management.

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    Not sure you can fix this (other than upgrading the software), there's a workaround on the client side though: ssh -oHostKeyAlgorithms=+ssh-dss -oKexAlgorithms=+diffie-hellman-group1-sha1 $HOST – Teun Vink Sep 28 '16 at 8:45
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As stated by @Teun Vink in comment, no way to do so but the given workaround using

ssh -oHostKeyAlgorithms=+ssh-dss -oKexAlgorithms=+diffie-hellman-group1-sha1 $HOST

do the trick.

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