Both eth0 and eth1 with the same ip?

sluge · 11-16-2012, 03:02 AM

Hello!
Just for fun I set to eth0 and eth1 the same IP. Wondering that it works! How is it possible? As i know, it is prohibited to use some IP twise in IPv4 subnet.

My output:

Code:

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE="eth0"
BOOTPROTO="static"
GATEWAY="192.168.207.1"
IPADDR="192.168.207.250"
NETMASK="255.255.255.0"
ONBOOT="yes"

# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE="eth1"
BOOTPROTO="static"
GATEWAY="192.168.207.1"
IPADDR="192.168.207.250"
NETMASK="255.255.255.0"
ONBOOT="yes"
TYPE="Ethernet"

eth0      Link encap:Ethernet  HWaddr 01:1C:22:6C:A1:32
          inet addr:192.168.207.250  Bcast:192.168.207.255  Mask:255.255.255.0
          inet6 addr: 2000:192:168:207:20c:29ff:fe6c:e13c/64 Scope:Global
          inet6 addr: fe80::20c:29ff:fe6c:e13c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2627 errors:0 dropped:0 overruns:0 frame:0
          TX packets:407 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:181446 (177.1 KiB)  TX bytes:38866 (37.9 KiB)

eth1      Link encap:Ethernet  HWaddr 11:AC:Z9:62:54:43
          inet addr:192.168.207.250  Bcast:192.168.207.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe6c:e146/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:721 errors:0 dropped:0 overruns:0 frame:0
          TX packets:28 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:113478 (110.8 KiB)  TX bytes:4159 (4.0 KiB)

]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.207.0   0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.207.0   0.0.0.0         255.255.255.0   U     0      0        0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U     1002   0        0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U     1003   0        0 eth1
0.0.0.0         192.168.207.1   0.0.0.0         UG    0      0        0 eth0

mandyapenguin · 11-16-2012, 03:22 AM

Ah, amazing!!! Don't know how?
Are these both interface connected simultaneously?

Code:

mii-tool

And also can you check whether there is no packet loss from both interface?

Code:

ping -I eth0 google.com

ping -I eth1 google.com

jefro · 11-16-2012, 05:54 PM

It is possible to do what you did. The underlying rules would eventually select which one the system would use. I forget them all but in all tcp/ip there are many not normally known rules for these issues.