Re: [LARTC] Masq/route based on port

[Miron <miron@hyper.to>]

I think we are on the same wavelength, except maybe exactly backwards. ;)

I'm trying to provide fast web browsing for clients that are on the 
internal network (talking to servers on the Internet).  Anything from 
the Internet with source port 80 should go through eth2.  Anything else 
should go through eth1.

I did some more investigation, and it seems that the Linux box is 
dropping all incoming packets arriving into eth2.  I can see packets 
with tcpdump, but the applications and NAT don't actually get it.  It 
must be getting dropped in the kernel.  It seems that this has something 
to do with the default route pointing to eth1.  I don't understand why 
the fact that the default route is not pointing to an interface should 
cause *incoming* packets to be dropped on that interface.

Sorry if my post was confusing.

Greg Scott wrote:

>>This is a home setup, not a server setup.  We have no servers on our 
>>network.  The reason we want port 80 on eth2 is because eth2 has more 
>>download bandwidth.  For other protocols we want eth1, because it has 
>>more symmetric bandwidth.
>>
>
>
>So anything that comes in from the Internet for port 80, no matter the 
>source, you want the reply to go back out on ETH2.  And anything that
>comes in from the Internet other than port 80, you want those replies to
>go out ETH1.  So the web server process is inside your Linux box?  
>
>Did I get that much right?  Or do I have it backwards?  
>
>The Linux box is your internal LAN's default gateway and you want this 
>box to decide which Internet interface to use, based on the destination 
>port your internal client PCs choose?  
>
>Hadn't thought about it that way before.
>
>- Greg
> 
>
>
>
>-----Original Message-----
>From: Miron [mailto:miron@hyper.to]
>Sent: Thursday, December 06, 2001 1:03 PM
>To: Greg Scott
>Cc: lartc@mailman.ds9a.nl
>Subject: Re: [LARTC] Masq/route based on port
>
>
>
>>I have following setup:
>>
>>- eth0 is an internal network
>>- eth1 is an Internet connection (IP = 1.1.1.128, GW=1.1.1.1)
>>- eth2 is another Internet connection (IP = 2.2.2.128, GW=2.2.2.1)
>>
>>I would like to masquerade port 80 through eth2, but all other traffic 
>>should be masq'ed through eth1.
>>
>>My routing configuration:
>>
>>   (default route in main table is 1.1.1.1)
>>
>>   ip rule add fwmark 2 pref 1002 table 666
>>
>>   ip route flush table 666
>>   ip route add default via 2.2.2.1 dev eth3 proto static table 666
>>   ip route flush cache
>>
>>My firewall configuration:
>>   iptables -t mangle -A PREROUTING -p tcp -m tcp --dport 80 -j MARK 
>>--set-mark 2
>>   iptables -t nat -A POSTROUTING -o eth1 -j SNAT --to-source 1.1.1.128
>>   iptables -t nat -A POSTROUTING -o eth2 -j SNAT --to-source 2.2.2.128
>>
>>Unfortunately, this does not work.  Outgoing packets are fine.  Incoming 
>>packets on port 80 are not de-masqueraded and do not reach the internal 
>>hosts.
>>
>>Also, if I change the ip rule above to be based on the source address 
>>(instead of a mark), connections start working fine.
>>
>>Here is the output of 'ip rule ls', to prove that I do have fwmark
>>
>compiled:
>
>>   0:      from all lookup local
>>   1002:   from all fwmark        2 lookup http
>>   32766:  from all lookup main
>>   32767:  from all lookup 253
>>
>>I am wondering if there is some kind of bug related to the interaction 
>>between fwmark and NAT. Any ideas?
>>
>>Thanks,
>>Miron Cuperman
>>
>
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