Re: [LARTC] Multiple network cards on same subnet problem

[Joe Nuts <joenuts@gmail.com>]

Hi Bram, 
I have a similar setup, and what I find works for me is adding ip
'rules' for certain traffic to have specific default routes.
for instance :

# ip rule add from 192.168.5.220 lookup 10
# ip route add table 10 default src 192.168.5.220 dev eth0

# ip rule add from 192.168.5.221 lookup 11
# ip route add table 11 default src 192.168.5.221 dev eth1

# ip rule add from 192.168.5.222 lookup 12
# ip route add table 12 default src 192.168.5.222 dev eth2

I hope that helps.
-Joe

On 5/2/05, Bram Matthys (Syzop) <syzop@vulnscan.org> wrote:
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> Hi,
> 
> this might seem like a classical problem but I've trouble getting this
> working correctly:
> 
> # ifconfig  ### output stripped down:
> eth0      Link encap:Ethernet  HWaddr 00:50:FC:2B:EB:1B
>          inet addr:192.168.5.220  Bcast:192.168.5.255  Mask:255.255.255.0
> 
> eth1      Link encap:Ethernet  HWaddr 00:02:44:60:EC:58
>          inet addr:192.168.5.221  Bcast:192.168.5.255  Mask:255.255.255.0
> 
> eth2      Link encap:Ethernet  HWaddr 00:20:ED:33:2B:6B
>          inet addr:192.168.5.222  Bcast:192.168.5.255  Mask:255.255.255.0
> 
> # ip route
> 192.168.5.0/24 dev eth0  proto kernel  scope link  src 192.168.5.220
> 192.168.5.0/24 dev eth1  proto kernel  scope link  src 192.168.5.221
> 192.168.5.0/24 dev eth2  proto kernel  scope link  src 192.168.5.222
> default via 192.168.5.11 dev eth0
> 
> # cat /proc/sys/net/ipv4/conf/all/arp_filter
> 1
> (and just to be sure I set /conf/<every interface>/arp_filter to 1 as well)
> 
> So basically what I want is just a box with 3 network cards with 3
> different ips, no bonding/trunking, just simple.. :).
> 
> What I get is simply that eth0 is answering (with it's own HW addr) to
> arp requests for all ips (so including .221 and .222). Also, the other
> interfaces are not answering (so it's not like they all answer either,
> only eth0 does). The interfaces do receive the request however (when I
> look with tcpdump).
> The effect is obvious, when I list the arp table on the client machine:
>  192.168.5.220         00-50-fc-2b-eb-1b     dynamic
>  192.168.5.221         00-50-fc-2b-eb-1b     dynamic
>  192.168.5.222         00-50-fc-2b-eb-1b     dynamic
>                            ^ that's all eth0's hw addr :|
> 
> I've also tried all /proc/sys/net/ipv4/conf/all/arp_ignore settings
> (+flushing arp tables @ client of course), but none of them helped...
> I'm not even sure if those options have anything to do with what I'm
> trying to accomplish.
> 
> Actually, when adding the hw addr manually (arp -s 192.168.5.221
> 00-02-44-60-EC-58) pinging doesn't work either... while all interfaces
> receive the request (because naturally the switch didn't see the arp
> request/reply it gets broadcasted) none of them replies.
> 
> Some of these are irrelevant, but just to be sure:
> - - no iptables rules are present
> - - all default iptables actions are at ACCEPT
> - - IP Forwarding is disabled
> - - I've reset my switch
> - - I've flushed all arp tables on both the server and test client machine
> 
> This is Linux 2.4.30 (w/grsecurity).
> 
> Fast switching is off btw, checked that as well.
> 
> Did I miss a setting? A kernel compile option? Or is there a problem
> with arp_filter in 2.4.*? I hope I'm missing something obvious here ;).
> 
> Thanks,
> 
>        Bram.
> 
> - --
> Bram Matthys
> Software developer/IT consultant        syzop@vulnscan.org
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