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Re: Pb : Routing with multiples interfaces

Hans van Kranenburg wrote:

Hey,


[...]
>

# LEASED LINE
ip rule add prio 203 from $NETWORK_LL/$PREFIX_LL table 203
ip route add default via $GATEWAY_LL dev $INTERFACE_LL src $IP_LL proto
static table 203
ip route append prohibit default table 203 metric 1 proto static


The src $IP_LL is specified in the ip route add line for table 203. So
the source address for the packet must be known and match $IP_LL,
otherwise this route will be ignored.

I seems you used this nice howto: http://www.ssi.bg/~ja/nano.txt Read
section '2.3.3 Setup of the default routes' again, carefully: "The
tricky part is, what the patches are doing here: They look at the local
source address" etc... is what I mean.



# SMTP MARK
ip rule add prio 103 fwmark 0x25 table 203



So table 203 gets looked up, but the default route to $INTERFACE_LL
won't get used. Instead one route of the multipath default route will be
chosen.



ip rule add prio 222 table 222
ip route add default table 222 proto static \
  nexthop via $GATEWAY_DSL1 dev $INTERFACE_DSL1 weight 10 \
  nexthop via $GATEWAY_DSL2 dev $INTERFACE_DSL2 weight 10 \
  nexthop via $GATEWAY_LL dev $INTERFACE_LL weight 1



I solved this problem by creating two extra routing tables. By directing
traffic which routing is forced to an outgoing line to a routing table
without the src address specified it matches a connectino that get
initiated.
I modified the STMP MARK rule and I created a new routing table (204), like this : 

#SMTP MARK
ip rule add prio 103 fwmark 0x25 table 204
ip route add default via $GATEWAY_LL dev $INTERFACE_LL proto static table 204 

But, I have the same problem :

# tcptraceroute -d -i eth2 -s 192.168.2.1 smtp.juliana-multimedia.com 25
debug: device set to eth2
debug: Discovered interface eth0 with address 192.168.1.1
debug: Discovered interface eth1 with address 192.168.0.1
debug: Discovered interface eth2 with address 192.168.2.1
debug: Determined source address of 192.168.1.1 to reach 213.223.240.194
The selected source address for the eth2 interface is 192.168.1.1, this is wrong, the good source address is 192.168.2.1 

I don't understand why the multipath default route is chosen.  :o(
Thes Linux Box receives the internal mail on its internal interface. Postfix/Amavis/Clamav/Spamassassin check this mail and sends it on the LL interface ($INTERFACE_LL - $IP_LL). 

I use these rules to mark the paquets :
iptables -t mangle -A OUTPUT -o $INTERFACE_DSL1 -p tcp --dport 25 -j MARK --set-mark 0x25 iptables -t mangle -A OUTPUT -o $INTERFACE_DSL2 -p tcp --dport 25 -j MARK --set-mark 0x25 iptables -t mangle -A OUTPUT -o $INTERFACE_LL -p tcp --dport 25 -j MARK --set-mark 0x25 

And these for NAT :
iptables -t nat -A POSTROUTING -o $INTERFACE_DSL1 -j SNAT --to-source $IP_DSL1 iptables -t nat -A POSTROUTING -o $INTERFACE_DSL2 -j SNAT --to-source $IP_DSL2 
iptables -t nat -A POSTROUTING -o $INTERFACE_LL -j SNAT --to-source $IP_LL


Regards.
--
==============================================
|              FREDERIC MASSOT               |
|     http://www.juliana-multimedia.com      |
|   mailto:frederic@juliana-multimedia.com   |
===========================Debian=GNU/Linux===
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