Linux does not detect link down?

naim.khan · 07-13-2007, 07:15 AM

Im new to Linux. Appreciate any help.

I have the following setup. I need to use Eth0 as primary link and Eth1 as its backup in case Eth0 goes down.

Chassis Server
-------- -------
|--|
| |------172.16.1.2/24---|--|----Eth0 172.16.1.1/24
10.16.131.174---| | | |
| |------192.168.1.2/24--|--|----Eth1192.168.1.1/24
|--|

Router - show ip route

C 10.16.131.0/24 Direct, Gi 5/12 0/0 03:24:04
C 172.16.1.0/24 Direct, Gi 5/10 0/0 00:06:38
C 192.168.1.0/24 Direct, Gi 5/11 0/0 03:36:58

Server:

[root@maa-101 ~]# /sbin/route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth1
172.16.1.0 * 255.255.255.0 U 0 0 0 eth0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth1
default 172.16.1.2 0.0.0.0 UG 10 0 0 eth0
default 192.168.1.2 0.0.0.0 UG 20 0 0 eth1
[root@maa-101 ~]#

Two default routes have been configured - through eth0 is with metric 10 and through eth1 is with metric 20.

I ping from server to 10.16.131.174 - as expected it takes the eth0 route through next hop 172.16.1.2.

When I disconnect the cable on g5/10, the alternate default gateway on the server through Eth1 does not take effect.

I see link LED not lit on eth0. But the route is not removed from the routing table. Nor is the link status shown as down in ifconfig.

Please help. Am I missing something? Is this how Linux behaves?

Thanks
Naim.

naim.khan · 07-13-2007, 07:25 AM

Bettering the ASCII ART

Chassis Server
-------- -------

|--|
| |-172.16.1.2/24---|--|-Eth0 172.16.1.1/24
10.16.131.174---| |
| |-192.168.1.2/24--|--|-Eth1192.168.1.1/24

nx5000 · 07-13-2007, 07:39 AM

Put [CODE] tags around

naim.khan · 07-13-2007, 08:35 AM

Put tags around?

nx5000 · 07-13-2007, 08:47 AM

Quote:

Originally Posted by naim.khan

Put tags around?

Around your nice ascii art

Before the ascii part, put "[ CODE ]" (without the space and quotes) and after, to stop it, put [/ CODE ](without the space).

Code:

|--|
|  |-172.16.1.2/24---|--|-Eth0 172.16.1.1/24
      10.16.131.174---| |
                      | |-192.168.1.2/24--|--|-Eth1192.168.1.1/24

naim.khan · 07-13-2007, 09:33 AM

Can you please tell me if the route through eth0 should not be flushed out?

Code:

Chassis                                         Server
--------                                        -------
 
 
                |--|
                |  |-172.16.1.2/24---|--|-Eth0 172.16.1.1/24
10.16.131.174---|  |                  
		|  |-192.168.1.2/24--|--|-Eth1192.168.1.1/24
                |--|

lazlow · 07-13-2007, 10:34 AM

You might have better luck configuring this with nic bonding in failover mode. This would give you two nics but one ip.

naim.khan · 07-13-2007, 01:17 PM

Hi Lazlow - The thing is we have one 10 gig and one 1 gig NIC. to make things easier, I used eth0 and eth1 to explain. So port-channel wont work. On the Router, 10 gig and 1 gig interfaces can not be bonded onto one channel. So theres a problem.

GregLee · 07-13-2007, 01:48 PM

In the Fedora 6 distribution, there are two services (daemons) to handle this. One detects a change in which network device is working best, and the other switches to it. I haven't tried this, personally, since I have at most one working network device, and I don't know what is comparable in other districutions.