Subject: Re: ssh hangs for a while waiting to connect
To: Andrew Basterfield <firstname.lastname@example.org>
From: Steven M. Bellovin <email@example.com>
Date: 03/05/2002 17:40:37
In message <firstname.lastname@example.org>, Andre
w Basterfield writes:
>On Tue, 05 Mar 2002 16:59:06 -0500
>"Johan A. van Zanten" <email@example.com> wrote:
>> I've seen similar delays. They only appear when using v2 of the SSH
>> protocol. v1 is fast. My initial theory is that the key sizes for v2 are
>> so large they outstrip the computational abilities of the slower
>> microSPARC (sun4m) CPUs. I'd love come to a different conclusion and
>> have a more workable ssh v2 on my NetBSD machines.
>Err... I'm using an SS2 so that's another league behind sun4m.
>I get a delay of approx 3 seconds before password prompt on an
>AMD486DX4/100 using SSH2, according to some rough measurements I did a
>while back decoding mp3s the SS2 lags the 486 by approximately 30% (and
>that was with inline assember on the 486 and none on the SS2).
>I'm not saying this is accurate or authoritive but it doesn't account for
>100fold performance gap between the two.
>I can ssh from the NetBSD/sparc machine to the same machine's IPv4 DNS
>name using SSH2 and get a password prompt in approx 5 seconds. This is
>around the timeframe I would be expecting, based on the response time of
>I'm not at all convinced it is purely a performace issue, it just doesn't
Can you run tcpdump on the network in question, to see what packets are
emitted? I see a long delay when running ssh to a 486/50 I have lying
around, but this sounds worse. I suspect a network cause, such as a
DNS timeout or a fruitless attempt at a v6 connection. You've
obviously thought about some of that, too, but it might be worth
looking at the wire to see what's actually happening.
--Steve Bellovin, http://www.research.att.com/~smb
Full text of "Firewalls" book now at http://www.wilyhacker.com