3.3 - ssh(1) takes a long time to connect or log in
Large delays (more that 10 seconds) are typically caused a problem with name resolution:
- Some versions of glibc (notably glibc 2.1 shipped with Red Hat 6.1) can take a long time to resolve "IPv6 or IPv4" addresses from domain names. This can be worked around with by specifying AddressFamily inet option in ssh_config.
- There may be a DNS lookup problem, either at the client or server. You can use the nslookup command to check this on both client and server by looking up the other end's name and IP address. In addition, on the server look up the name returned by the client's IP-name lookup. You can disable most of the server-side lookups by setting UseDNS no in sshd_config.
Delays less than 10 seconds can have other causes.
- OpenSSH releases prior to 3.8 had an moduli file with moduli that were just smaller than what sshd would look for, and as a result, sshd would end up using moduli significantly larger than requested, which resulted in a speed penalty. Replacing the moduli file will resolve this (note that in most cases this file will not be replaced during an upgrade and must be replaced manually).
- OpenSSH releases prior to 3.8 had a flaw in ssh that would cause it to request moduli larger than intended (which when combined with the above resulted in significant slowdowns). Upgrading the client to 3.8 or higher will resolve this issue.
- If either the client or server lack a kernel-based random number device (eg Solaris < 9, AIX < 5.2, HP-UX < 11.11) and no substitute is available (eg prngd) it's possible that one of the programs called by ssh-rand-helper to generate entropy is hanging. This can be investigated by running it in debug mode: /usr/local/libexec/ssh-rand-helper -vvv
Any significant delays should be investigated and rectified, or the corresponding commands should be removed from ssh_prng_cmds.