In my network configuration, I have three switches:

  1. Internet (xx.xx.140.129/25)
  2. Internal SAN (
  3. iLo management (

I have one Linux server which I use for management that needs to have access to all three networks, however it only has 2 NICs. I've cabled switches #2 and #3 together, so there is a physical path between them, and I've tried ip route add eth0, but that did not work. Any ideas on how this could be done?

[root@ilo]# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
XX.XX.140.128  U     0      0        0 eth1   U     0      0        0 eth0   U     0      0        0 eth0     U     0      0        0 eth1         XX.XX.140.129         UG    0      0        0 eth1
  • What did not work in your config? Which network tests are failing? May 7, 2012 at 20:30
  • please show output from ifconfig
    – Peter
    May 8, 2012 at 12:11
  • or "ip addr" if you prefer (to be consistent since you are using "ip ..." for the rest)
    – Peter
    May 8, 2012 at 12:14

2 Answers 2


If you want to separate the traffic for security reasons, you should use VLAN tagging. For this you will need managed switches.

If you do not need to separate the traffic for security, then you should use the same IP prefix for #2 and #3

If you still want to use your design, (e.g. if you plan to separate the networks later with managed switches), then you can use IP aliases (add secondary IP addresses) on an interface.

To debug your network problem go on the network stack from physical layer to the application one:

  1. test your cables. Do you have link up on all interfaces on the path? e.g. all ethernet LEDs are blinking for all interfaces?
  2. is the device answering to arping, ping. Try both using IP and hostname.
  3. run traceroute and see how the packets are routed. Debug with ip route get <IP_destination> to find on which interface will the packets get routed.
  4. use telnet, nc, etc. to see if the application is answering.

EDIT: Run:

ip route del dev eth0   # remove the fixed route
ip addr add dev eth0    # add an IP alias 

The problem is that you do not have an IP from prefix on the eth0.

  • <pre>tracert traceroute to (, 30 hops max, 40 byte packets 1 ( 3000.008 ms !H 3000.010 ms !H 3000.006 ms !H
    – John P
    May 8, 2012 at 2:32
  • arping ARPING from eth0 Sent 49 probes (49 broadcast(s)) Received 0 response(s)
    – John P
    May 8, 2012 at 2:32
  • arping works only if the 2 devices are in the same VLAN. May 8, 2012 at 2:38
  • Is it working with ip addr add ... ? May 8, 2012 at 17:47

Setting the route is only part of the game, but how does the internal SAN network know how to get to your It's missing it's route back.

Simplest solution: assign an IP of subnet to your eth0:

ip addr add 10.1.1.xyz/24 dev eth0

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