[SOLVED] How do I diagnose a Network problem? CentOS 6.3
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I've dabbled in CentOS for years, and have never figured out a number of things. Today, help me to understand how to diagnose Networking. I have a production server sitting in a server farm: epsilon.scubaboard.com. It's hosting a few not-so-important web sites, but I do need to get it up and running quickly. I was playing around on a non-production server beta.scubaboard.com which I could only ssh into on the local IP. (192.168.2.20) Anyway, I was reading about how to implement NetworkManager and yum installed the beast. Only I wasn't on beta. The connection had closed and I was on epsilon. Everything ground to a halt and ultimately I could only ssh into it from another local server. I played around with a number of settings, mostly leaving them intact. I did play with resolv.conf and I don't remember any others. It was about this time I realized that I had inadvertently installed NetworkManager and yum remove NetworkManager seemed to resolve everything. I could ssh in on a public IP, I could ping out and all the sites were back up: Yay! Then I rebooted the server and it all went to hell.
Right now, I want to figure out why I can't ping 8.8.8.8. Somehow I have stopped the ability of the server to see the rest of the interwebs. Here are some test results:
The non-production server has a similar problem. If I fix the one, the other issue should be obvious.
Don't talk to me of resolv.conf this is not a DNS issue. Here's my ifcnfg -all output:
Shutting down interface eth0: [ OK ]
Shutting down interface eth1: [ OK ]
Shutting down loopback interface: [ OK ]
Bringing up loopback interface: [ OK ]
Bringing up interface eth0: Determining if ip address 192.168.2.70 is already in use for device eth0...
[ OK ]
Bringing up interface eth1: Determining if ip address 69.28.64.172 is already in use for device eth1...
[ OK ]
How does that help me to diagnose any Networking problem? I posted in the title that it's CentOS 6.3. I can't do an update if I can't get to the interwebs, now can I?
on a server you should not need the wireless and VPN dynamic "network manager"
also "network" and "network manager" can NOT !!! both be turned on
disable "network manager" and turn on "network"
also unless you really using ipv6 you might want to disable that
dhcp has a 5 min. time out and if it is looking for a ipv6 address that can not be looked up
as in 8.8.8.8 and 8.8.4.4 is googles ipv4 address
this will first try to use ipv6
time out
then try the ipv4 address
NetworkManager has been stopped and then removed as per the OP. How do I diagnose if Network is working? I even posted the output of service network restart in the OP.
Telling me to disable one and to turn on the other doesn't give me the direction I need. What commands I need to use to do this would be helpful.
Quote:
Originally Posted by John VV
on a server you should not need the wireless and VPN dynamic "network manager"
also "network" and "network manager" can NOT !!! both be turned on
disable "network manager" and turn on "network"
also unless you really using ipv6 you might want to disable that
dhcp has a 5 min. time out and if it is looking for a ipv6 address that can not be looked up
as in 8.8.8.8 and 8.8.4.4 is googles ipv4 address
this will first try to use ipv6
time out
then try the ipv4 address
It's my opinion that there is a clear cut way to diagnose Network connectivity issues. Surely, someone knows how to diagnose why I can't ping out, even though I can ssh in on a private IP.
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:30:48:35:2a:32 brd ff:ff:ff:ff:ff:ff
inet 192.168.2.70/24 brd 192.168.2.255 scope global eth0
inet6 fe80::230:48ff:fe35:2a32/64 scope link
valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:30:48:35:2a:33 brd ff:ff:ff:ff:ff:ff
inet 69.28.64.172/28 brd 69.28.64.175 scope global eth1
inet 209.208.25.243/29 brd 209.208.25.247 scope global eth1:1
inet 209.208.92.36/28 brd 209.208.92.47 scope global eth1:10
inet 209.208.92.41/27 brd 209.208.92.63 scope global eth1:11
inet 209.208.25.244/29 brd 209.208.25.247 scope global secondary eth1:2
inet 209.208.92.35/27 brd 209.208.92.63 scope global secondary eth1:3
inet 209.208.25.246/29 brd 209.208.25.247 scope global secondary eth1:4
inet 209.208.92.37/27 brd 209.208.92.63 scope global secondary eth1:6
inet 209.208.92.38/27 brd 209.208.92.63 scope global secondary eth1:7
inet 209.208.92.39/27 brd 209.208.92.63 scope global secondary eth1:8
inet 209.208.92.40/27 brd 209.208.92.63 scope global secondary eth1:9
inet6 fe80::230:48ff:fe35:2a33/64 scope link
valid_lft forever preferred_lft forever
ip route
Code:
209.208.25.240/29 dev eth1 proto kernel scope link src 209.208.25.243
209.208.92.32/28 dev eth1 proto kernel scope link src 209.208.92.36
69.28.64.160/28 dev eth1 proto kernel scope link src 69.28.64.172
209.208.92.32/27 dev eth1 proto kernel scope link src 209.208.92.41
192.168.2.0/24 dev eth0 proto kernel scope link src 192.168.2.70
169.254.0.0/16 dev eth0 scope link metric 1002
169.254.0.0/16 dev eth1 scope link metric 1003
default via 69.28.64.162 dev eth1
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