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 From:  "Eric Shorkey" <eshorkey at commonpointservices dot com>
 To:  "Christiaens Joachim" <jchristi at oce dot be>
 Cc:  <m0n0wall at lists dot m0n0 dot ch>
 Subject:  Re: [m0n0wall] smtp delay over 2 firewalls with one bridging
 Date:  Tue, 23 Mar 2004 18:31:11 -0500
Just to clear things up for people. I mentioned that the reverse dns on the
mailserver was very fast in my original message. I was kind of hidden at the
bottom though. Believe me, I initially thought dns was the problem too, but
it isn't.

As for the routing issue, the routing tables aren't doing anything wierd.
Packets come and go via the same route.

I'm beginning to think this is going to require me to plug a laptop into the
dmz with a packet sniffer. I was hoping someone might have ran into this
already, but it's not looking that way. I'll let everyone know if I find

----- Original Message ----- 
From: "Christiaens Joachim" <jchristi at oce dot be>
To: "'Eric Shorkey'" <eshorkey at commonpointservices dot com>
Cc: <m0n0wall at lists dot m0n0 dot ch>
Sent: Tuesday, March 23, 2004 8:12 AM
Subject: RE: [m0n0wall] smtp delay over 2 firewalls with one bridging

> -----Original Message-----
> From: Eric Shorkey [mailto:eshorkey at commonpointservices dot com]
> Sent: dinsdag 23 maart 2004 12:23
> To: m0n0wall at lists dot m0n0 dot ch
> Subject: [m0n0wall] smtp delay over 2 firewalls with one bridging
> This is an interesting setup, hopefully someone out there can
> recreate it and tell me if I'm a loon or not.
> Here is the problem:
> I'm experiencing significant connection delays when
> contacting port 25 of my mailserver. The connection seems to
> always go through, it just takes about 20 seconds before the
> connection is established.
> The setup:
> I have 5 public ip addresses (it's a /29 ip block). Due to
> some software I run on most of these ip addresses, I have to
> firewall #1 in bridging mode between the wan and the lan.
> Firewall #1 uses one of those public ip addresses for it's
> WAN port as well, since it insists on having an ip address.
> The interesting thing is firewall #2. It is using another of
> those 5 ip addresses on it's wan port. Both of these
> firewalls' WAN ports are connected to a hub, and that hub is
> also plugged into my internet provider's equipment. These 2
> firewalls are protecting the same network, it's purely set up
> this way because m0n0wall won't route out a bridged interface.
> My mailserver has multiple network cards, and it's default
> route is to push out to the public router for internet
> traffic. One of the network cards is an internet card, and
> another is for the secured network only.
> The twist:
> When connecting to my mailserver using only internal ip
> addresses, everything runs nice and fast. No delays at all.
> Only when I'm connecting to the mailserver using the public
> ip address do I experience the delay.
> I've tried using proxy arp to force the firewall to publish
> the ip on the wan card of firewall #1, but that didn't help.
> (I didn't expect it to, I was grasping at straws.) I'd think
> it's an arp problem, but it only does this on port 25, so
> it's very strange. It couldn't really be a dns related issue
> either. The reverse lookup for ip addresses on the mailserver
> is very fast, so it's not like the smtp server is waiting for
> dns. I've even tried setting up rules to specifically block
> packets destine for firewall #2's ip address from finding
> their way into the bridged interface on firewall#1. Doesn't
> help. I've reset the state on both firewalls, that didn't help either.
> So, I'm kind of at a loss on this one. The setup should work,
> and it's sane, but I may end up having to change my network
> design a little to help m0n0wall cope with it. It works for
> now, the delay is just a little annoying. Figured I'd bounce
> this one off the mailing list to see what people have to say about it.
> Cheers!
> Eric

Just a guess: do packets get routed/bridged the same way from and to the
client/server? In other words: do packets follow the same 'road'? This seems
to give different results for different
Some OS'es 'learn' about routes or short-cuts to routers and place these
'learned' routes above more general ones, which could add another twist.
I would look at routing tables and traceroutes and draw a nice diagram :)


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