[LARTC] Policy routing question

From: Peter Rabbitson <rabbit@rabbit.us>
To: lartc@vger.kernel.org
Subject: [LARTC] Policy routing question
Date: Mon, 13 Aug 2007 22:30:53 +0000	[thread overview]
Message-ID: <46C0DB9D.3000104@rabbit.us> (raw)

Hi,

I have a testing multihome setup, with the default gateway being one of 
the links and using policy routing to honor requests for a specific 
link. Everything works as expected when I request a specific IP to bind 
to. But if I request a specific interface things fall apart in ways that 
I can not explain:

default gw (WORKS)
----------
rabbit@Thesaurus:~$ ping -c 1 yahoo.com
PING yahoo.com (216.109.112.135) 56(84) bytes of data.
64 bytes from w2.rc.vip.dcn.yahoo.com (216.109.112.135): icmp_seq=1 
ttlH time\x142 ms

request IP on same link as default gw (WORKS)
-------------------------------------
rabbit@Thesaurus:~$ ping -I 192.168.9.102 -c 1 yahoo.com
PING yahoo.com (66.94.234.13) from 192.168.9.102 : 56(84) bytes of data.
64 bytes from w2.rc.vip.scd.yahoo.com (66.94.234.13): icmp_seq=1 ttlG 
time\x176 ms

request IP on secondary link (WORKS)
----------------------------
rabbit@Thesaurus:~$ ping -I 172.16.0.2 -c 1 yahoo.com
PING yahoo.com (216.109.112.135) from 172.16.0.2 : 56(84) bytes of data.
64 bytes from w2.rc.vip.dcn.yahoo.com (216.109.112.135): icmp_seq=1 
ttlG time\x146 ms

request interface of default gw link (WORKS)
------------------------------------
rabbit@Thesaurus:~$ ping -I eth1 -c 1 yahoo.com
PING yahoo.com (66.94.234.13) from 192.168.9.102 eth1: 56(84) bytes of data.
64 bytes from w2.rc.vip.scd.yahoo.com (66.94.234.13): icmp_seq=1 ttlG 
time\x176 ms

request secondary interface (FAILS)
---------------------------
rabbit@Thesaurus:~$ ping -I eth0 -c 1 yahoo.com
PING yahoo.com (216.109.112.135) from 192.168.9.102 eth0: 56(84) bytes 
of data.
 From 172.16.0.2 icmp_seq=1 Destination Host Unreachable

I went over the setup again and again, but I can't figure out why the 
last ping attempt fails. Any pointers are welcome!

Thanks

Peter

Here is the setup:

ip addr
----------
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
     link/ether 00:11:09:8d:4f:c1 brd ff:ff:ff:ff:ff:ff
     inet 172.16.0.2/24 brd 172.16.0.255 scope global eth0
3: eth1: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
     link/ether 00:04:e2:80:b4:97 brd ff:ff:ff:ff:ff:ff
     inet 192.168.9.102/24 brd 192.168.9.255 scope global eth1

ip ro show table all
-----------------------
default via 172.16.0.1 dev eth0  table 10
default via 192.168.9.1 dev eth1  table 20
default via 192.168.9.1 dev eth1  table default
172.16.0.0/24 dev eth0  proto kernel  scope link  src 172.16.0.2
192.168.9.0/24 dev eth1  proto kernel  scope link  src 192.168.9.102
broadcast 127.255.255.255 dev lo  table local  proto kernel  scope link 
  src 127.0.0.1
broadcast 192.168.9.0 dev eth1  table local  proto kernel  scope link 
src 192.168.9.102
broadcast 172.16.0.0 dev eth0  table local  proto kernel  scope link 
src 172.16.0.2
local 192.168.9.102 dev eth1  table local  proto kernel  scope host  src 
192.168.9.102
local 172.16.0.2 dev eth0  table local  proto kernel  scope host  src 
172.16.0.2
broadcast 192.168.9.255 dev eth1  table local  proto kernel  scope link 
  src 192.168.9.102
broadcast 172.16.0.255 dev eth0  table local  proto kernel  scope link 
src 172.16.0.2
broadcast 127.0.0.0 dev lo  table local  proto kernel  scope link  src 
127.0.0.1
local 127.0.0.1 dev lo  table local  proto kernel  scope host  src 
127.0.0.1
local 127.0.0.0/8 dev lo  table local  proto kernel  scope host  src 
127.0.0.1

ip ru
-----
0:      from all lookup local
5:      from all lookup main
10:     from all iif eth0 lookup 10
11:     from 172.16.0.0/24 lookup 10
20:     from all iif eth1 lookup 20
21:     from 192.168.9.0/24 lookup 20
100:    from all lookup default

no netfilter rules of any sort (all policies set at ACCEPT)

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