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List:       linux-virtual-server
Subject:    Re: [lvs-users] LVS-NAT problems for SMTP cluster
From:       infernix <infernix () infernix ! net>
Date:       2008-05-03 18:40:11
Message-ID: 481CB18B.8090404 () infernix ! net
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Joseph Mack NA3T wrote:
> On Sat, 3 May 2008, Jason Ledford wrote:
> 
> > I am doing a smtp cluster and after I got the lvs part figured out, smtp works \
> > just fine.  In your telnet session, how do you get as far as the mail from and \
> > rcpt to if you aren't getting a response?  If you telnet to the server does it \
> > respond with a banner?
> I think there's the beginnings of the exchange in the HOWTO

I dug through it again, but couldn't find a more detailed description of 
the packet flow than I already laid out.

> > I've given LVS-DR a spin and that worked fine, but the issue with that
> > is that outgoing SMTP messages (e.g. sendmail queue) would be sent from
> > the various real server public source IPs.
> 
> what public IPs? For security, the only public IP on the 
> realserver should be the VIP

The realservers had an unique public IP + the VIP on lo:1. But i do 
suppose we could change the LVS-DR setup with iproute2 rules so that I 
can get the outgoing SMTP traffic NATed over the VIP on the director, I 
saw some patches about that. Anyhow, that's irrelevant for the LVS-NAT 
issue I'm having.

> > When I've done this, I am getting traffic all the way: client >
> > (internet) > gateway 80.1.1.1 >  VIP on director > RIP on real server >
> > back to director (ipvs?) > gateway 80.1.1.1 > (internet) > client.
> 
> so the LVS is working

No, not really. Look at the twake or tcpdump logs; the realserver keeps 
retransmitting the TCP packets but the client doesn't seem to tie them 
to the active TCP session (regardless of what client is used, whether a 
local address in the public range or any random public IP on the 
internet). So it seems that something is going wrong with the TCP 
session. Perhaps redundant, but I replied this in another post:

mx-node01:~# nc -p 25 -l
client:~# nc 80.1.1.10 25

When I type text in the client nc session, this text shows up on the
realserver netcat session.

When I type text in the *realserver* netcat session, it *doesn't* show
up at the client netcat session.

It is as if the data in the tcp session is one-way, e.g. data only goes
from client -> server. My TCP knowledge isn't good enough to figure out 
why this happens.


> I don't really know what's going on. Since LVS is working, 
> there must be something at the application layer. Is 
> localhost a valid address in this context?

All nodes have just 127.0.0.1 configured on lo, if that's what you mean.

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