Re: Two NICS with same IP and same client IP

[Tom Eastep <teastep@shorewall.net>]

Raphael Jacquot wrote:
> Hervé wrote:
> 
>> Hello,
>>
>> I have a weird setup I would like to make work: I have two identical
>> subnets connected to one machine via two different NICs, like this:
>>
>> Server             |         | Client 1
>> eth0:192.168.100.1 |---------| 192.168.100.2
>>                    |                              | Client 2
>> eth1:192.168.100.1 |------------------------------| 192.168.100.2
> 
> 
> having 2 interfaces on the same box with the same IP address
> 
> repeat after me :
> 
> WILL NOT WORK

Having two interfaces with the same IP address and netmask doesn't work
well. Having the same IP address with different netmasks can be useful.

From my firewall:

gateway:/usr/src/linux-2.6.10/net/ipv4/netfilter# ip addr ls
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:a0:cc:db:31:c4 brd ff:ff:ff:ff:ff:ff
    inet 206.124.146.176/32 scope global eth0
    inet6 fe80::2a0:ccff:fedb:31c4/64 scope link
       valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc htb qlen 1000
    link/ether 00:02:e3:08:55:fa brd ff:ff:ff:ff:ff:ff
    inet 206.124.146.176/24 brd 206.124.146.255 scope global eth1
    inet 206.124.146.178/24 brd 206.124.146.255 scope global secondary
eth1:0
    inet 206.124.146.180/24 brd 206.124.146.255 scope global secondary
eth1:1
    inet6 fe80::202:e3ff:fe08:55fa/64 scope link
       valid_lft forever preferred_lft forever
4: eth2: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether 00:08:c7:c0:e2:15 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.254/24 brd 192.168.1.255 scope global eth2
    inet6 fe80::208:c7ff:fec0:e215/64 scope link
       valid_lft forever preferred_lft forever
5: sit0: <NOARP> mtu 1480 qdisc noop
    link/sit 0.0.0.0 brd 0.0.0.0
gateway:/usr/src/linux-2.6.10/net/ipv4/netfilter#

Note Interfaces eth0 and eth1 -- both have IP address 206.124.146.176.

eth0 interfaces to my DMZ where there is a single server
(206.124.146.177) using Proxy ARP.

-Tom
-- 
Tom Eastep    \ Nothing is foolproof to a sufficiently talented fool
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