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I have 2 centos 5 servers, directly connected via an ethernet cable(not sure it's a crossover cable or straight through), but they can not ping each other. This did work at some point, but I believe stopped working yesterday.

Unfortunately this is a remote server, so I'm limited to what I can test over ssh or remote console access, i.e., I can't just replace the cable.

ethtool and mii-tool both show the nics connected, auto-negotiated at 1000/full. iptables is off, and selinux is disabled.

I have tried restarting the network interface on both, forcing them to renegotiate, even went so far as rebooting both servers. nothing looks out of place in the configs to me, so I'm at a loss here.

Server1 config:

route -n:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     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     0      0        0 eth1
10.90.0.0       0.0.0.0         255.255.0.0     U     0      0        0 eth0
0.0.0.0         10.90.250.1     0.0.0.0         UG    0      0        0 eth0

ifcfg file:

DEVICE=eth1
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.7
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
IPV6_AUTOCONF=yes

ifconfig output:

eth1      Link encap:Ethernet  HWaddr 00:15:17:66:99:C5  
          inet addr:192.168.1.7  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::215:17ff:fe66:99c5/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2633 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1530 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:168952 (164.9 KiB)  TX bytes:137137 (133.9 KiB)
          Base address:0x2000 Memory:b8800000-b8820000 

Server2 config:

route -n:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     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     0      0        0 eth1
10.90.0.0       0.0.0.0         255.255.0.0     U     0      0        0 eth0
0.0.0.0         10.90.250.1     0.0.0.0         UG    0      0        0 eth0

ifcfg file:

DEVICE=eth1
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.8
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
IPV6_AUTOCONF=yes

ifconfig output:

eth1      Link encap:Ethernet  HWaddr 00:15:17:66:9A:2D  
          inet addr:192.168.1.8  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::215:17ff:fe66:9a2d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:5857 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7035 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:375200 (366.4 KiB)  TX bytes:728319 (711.2 KiB)
          Base address:0x2000 Memory:b8800000-b8820000 

Any ideas or suggestions would be greatly appreciated.

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Does arp show the other machine on either box? What does tcpdumping the interface show when you try to ping? Do either boxes see any packets from the other machine? If tcpdump isn't seeing anything then there is probably a physical layer issue... –  polynomial Oct 1 '11 at 18:00
    
tcpdump shows nothing besides arp requests (which fail). the arp table shows "(incomplete)" on both sides. I manually input arp entries, but it didn't make a difference. I'm inclined to believe it's a hardware issue, but I was hoping someone would have some insight I was missing. –  ben Oct 1 '11 at 18:22
    
You could try and use mii-tool to configure them at a lower speed. It is possible the cable is going bad but 100/full might still work. –  polynomial Oct 1 '11 at 18:28
    
excellent suggestion, thank you. Unfortunately, it didn't make a difference, but it was something I hadn't thought of. –  ben Oct 1 '11 at 18:54

2 Answers 2

I've seen problems like these when the CentOS driver does not fully support the network card, such as some network adapters for HP Proliant servers. Try searching for a driver provided by the card manufacturer or integrator and applying it.

share|improve this answer
    
thanks for the suggestion, I have also seen issues like this, and it's a valid suggestion for anyone else with a similar problem. I'd vote this up, but I don't have enough reputation, sorry. –  ben Feb 2 '12 at 23:21
up vote 1 down vote accepted

Turns out the answer was human error. An on-site tech thought the servers were supposed to be connected to the switch, and changed them without mentioning it to anyone else. Thanks for the suggestions polynomial and joechip.

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