Re: [LARTC] Wierd Policy Routing Behaviour

[Alexey Talikov <alexey_talikov@texlab.com.uz>]

Without iproute
iptables -t nat -A POSTROUTING -s $SMTP -p tcp --sport 1024: --dport 25 -j SNAT --to-source $IP_B


30.05.2002 19:05:13, Sellaro <sellaro@email.it> wrote:

>Hi there 
>
>I'm trying to set up policy routing in a simple scenario without further
>success. My linux router is connected to two different cable ISPs. One
>of these links (hereafter named A) permits traffic to SMTP servers while
>the other (link B) doesn't. 
>
>What I am trying to set up is: all traffic should flow through link B
>and only SMTP traffic through link A. 
>
>What I am doing: 
>
>Marking all packets from my intranet with source port within the range
>1024 to 65535 and with destination port 25 with mark 0x3. I am also
>marking packets from our internal SMTP server with source port 25 to any
>other port with the same mark. Marks are being made in the OUTPUT chain
>(using iptables) as follows: 
>
>iptables -t mangle -A OUTPUT -p tcp --sport 1024:65535 --dport 25 -j
>MARK --set-mark 3 
>
>iptables  -t mangle -A OUTPUT -p tcp -s <MY SMTP SERVER> --sport 25 -j
>MARK --set-mark 3 
>
>Then, I have created a new routing table named SMTP-ROUTE with default
>gateway being the default gateway for link A as follows: 
>
>ip ro add default via <A's default GW> table SMTP-ROUTE 
>
>To complete the setup, I've added a rule stating that all packets marked
>with 0x3 should use SMTP-ROUTE with this command: 
>
>ip ru add fwmark 3 table SMTP-ROUTE 
>
>Yes, I've flushed the routing cache with: 
>
>ip ro flush cache 
>
>Default route in main routing table is B's gateway. 
>
>I don't know why, but SMTP traffic keeps going through B's gateway,
>instead of A's, as expected. 
>
>I've sniffed the network and, in fact, the packets are trying to go out
>through B's gateway.
>
>Can anyone please point what I am doing wrong?
>
>Thank you in advance 
>-- 
>Sellaro
>
>Agente Livre - Linux Community (www.agentelivre.org)
>
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>
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-----------------------------------
mailto:alexey_talikov@texlab.com.uz
BR
Alexey Talikov
FORTEK
-----------------------------------


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