[vox-tech] ssh login slow with iptables

[Samuel Merritt]

Jack LaPlante said:
> I'm setting up my nifty new dedicated web server with a firewall
> like this: (I'm on RH9, the rpms look like the latest avail )
>
> iptables -F
> iptables -A INPUT -i lo -j ACCEPT
> iptables -A INPUT -m multiport -p tcp --dport www,ssh,sftp,smtp,10000 \
> -j  ACCEPT
> iptables -A INPUT -j LOG -m limit
> iptables -A INPUT -j REJECT
>
> (an o'reilly setup from the linux security cookbook)
>
> Now, when I log in via SSH or SFTP, there is a 30 second pause while my
> password authorizes.  It used to take a second or two.  Flush the rules
> and the login is up to speed again.

You don't allow inbound 53/udp, so your machine can't use DNS. By default,
sshd looks up the name of the connecting machine, and it looks like the
DNS lookup takes 30 seconds to time out.

> I want to force my clients to use SFTP for all their file transfers but
> the delay is going to be annoying.
>
> Any suggestions to speed up my logins?

iptables -A INPUT --source $DNS_SERVER_IP_HERE -p udp --sport 53 -j ACCEPT

Assuming I got the syntax right, do that once for each DNS server you have.

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