Backup lan eth1 is not getting pinged from the network

[sanwin]

Hi,
How to troubleshoot the lan interface issues in linux.

There are two lans in a linux box.
Backup lan is not getting pinged from the network. If we do a traceroute it is getting expired at a particular ip address.

Is there any way to troubleshoot the same.

regards,
sanwin

[Ivan Ferreira]

Check link conecctivity with ethtool eth1.

Check if iptables firewall is enabled with "service iptables status"

Check if the ip address and subnet mask is correct and the interface is up with "ifconfig".

Check your routing tables with netstat -nr.

Post the results.

[sanwin]

Thanks for the quick reply Ivan!!

Here is the output: Please help me if you have some comments on the output.

eth0 is the normal lan which is working and eth1 is the backup lan which is not pinging.
[root@ras root]# ethtool eth1
Settings for eth1:
Supported ports: [ MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Advertised auto-negotiation: Yes
Speed: Unknown! (65535)
Duplex: Unknown! (255)
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: g
Wake-on: d
Current message level: 0x000000ff (255)
Link detected: no


[root@ras root]# ethtool eth0
Settings for eth0:
Supported ports: [ MII ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: Not reported
Advertised auto-negotiation: No
Speed: 100Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: off
Supports Wake-on: g
Wake-on: d
Current message level: 0x000000ff (255)
Link detected: yes


[root@ras root]# service iptables status
Firewall is stopped.

[root@ras root]# netstat -nr
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
172.25.4.0 0.0.0.0 255.255.254.0 U 0 0 0 eth1
172.25.8.0 0.0.0.0 255.255.248.0 U 0 0 0 eth0
224.0.0.0 0.0.0.0 240.0.0.0 U 0 0 0 eth0
0.0.0.0 172.25.8.59 0.0.0.0 UG 0 0 0 eth0


thanks!!

regards,
sanwin

[Ivan Ferreira]

From the output of ethtool you can see:

Link detected: no

You have a problem with your cable, or switch. Check the network adapters lights if it has it.