On Tue, Dec 24, 2013 at 12:52 AM, <mikep at noc.utoronto.ca> wrote: > On Wed, 13 Nov 2013, Loganaden Velvindron wrote: > >> On Wed, Nov 13, 2013 at 2:05 AM, Darren Tucker <dtucker at zip.com.au> wrote: >>> >>> On Tue, Nov 12, 2013 at 4:40 PM, <mikep at noc.utoronto.ca> wrote: >>> >>>> Just upgraded to OpenSSH_6.4 with OpenSSL 1.0.1e and libz.so.1.2.8. >>>> Now some (but not all) Cisco router logins hang: >>>> >>>> debug1: sending SSH2_MSG_KEXDH_INIT >>>> debug1: expecting SSH2_MSG_KEXDH_REPLY >>>> [hangs] >>>> >>> >>> Suggestions in approximate order of likelihood. >>> - the additional KexAlgorithms exceed some static buffer in the Cisco. >>> Try: >>> "KexAlgorithms >>> diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1" >>> - you have some kind of path MTU problem and the extra traffic from the >>> additional algorithms pushes you past some packet boundary. Check the >>> "send-q" column on client and the equivalent on the server and see if >>> they're non-zero and non-decreasing). >> >> >> Shouldn't Mike open a ticket at CISCO so that they start fixing the >> software on their side as well ? > > > Sorry to have taken so long to get back to you about this - your suggestion > about "KexAlgorithms" caused me to test a lot of combinations to find what > will work. It turns out the Cisco SSH server only supports a limited set of > ciphers (this is documented sort-of by Cisco, and is displayed when you try > to force a non-supported cipher). That's short-sighted coming from them. I have tested and I have the same problem with the latest snapshot. This is very annoying. Do you have a ticket number where I can also chip in ? > > This in turn seems to limit the key exchange mechanisms that will work. > > Forcing a cipher with '-c' also appears to force something in the Kex for > OpenSSH; I can't find anything about Kex in any Cisco docs. > > I have created a special section of the 'ssh_config' file for those devices > with these options, and all seems to be working fine: > > Ciphers aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc > KexAlgorithms > diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchan > ge-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 > > Thank you for the help! > > >>>> Originally I had 'Cipher blowfish' set in '/etc/ssh/ssh_config', but >>>> removing that makes no difference. >>> >>> >>> That's because Cipher affects only Protocol 1 (which was some time in the >>> past the only version at least some Cisco devices spoke). >>> >>>> However, forcing '-c 3des' does >>>> allow it to work (even though '3des' is supposed to be the default): >>> >>> >>> 3des is the default Cipher Protocol 1. Protocol 2 takes a list (Ciphers) >>> and its default is >>> >>> aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128, >>> aes128-gcm at openssh.com,aes256-gcm at openssh.com, >>> aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc, >>> aes256-cbc,arcfour >>> >>> the -c option overrides both. >>> >>> -- >>> Darren Tucker (dtucker at zip.com.au) >>> GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69 >>> Good judgement comes with experience. Unfortunately, the experience >>> usually comes from bad judgement. >>> _______________________________________________ >>> openssh-unix-dev mailing list >>> openssh-unix-dev at mindrot.org >>> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev > > > Mike > -- > Mike Peterson Information Security Analyst - > Audit > E-mail: mikep at noc.utoronto.ca WWW: > http://www.noc.utoronto.ca/ > Tel: 416-978-5230 Fax: > 416-978-6620 -- This message is strictly personal and the opinions expressed do not represent those of my employers, either past or present.
