LinuxQuestions.org
Latest LQ Deal: Complete CCNA, CCNP & Red Hat Certification Training Bundle
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Newbie
User Name
Password
Linux - Newbie This Linux forum is for members that are new to Linux.
Just starting out and have a question? If it is not in the man pages or the how-to's this is the place!

Notices


Reply
  Search this Thread
Old 11-03-2010, 10:19 AM   #1
2Hugh
LQ Newbie
 
Registered: Sep 2010
Location: Guildford, UK
Distribution: Red Hat 4 update 5
Posts: 9

Rep: Reputation: 0
Question destination network unreachable


Happily using VNCviewer to work on my RedHat server the other day, when suddenly, I lost contact.

The server is still up.

Retrying the connection via VNC I get a timeout.
Doing a ping from my client to the server IP, I get host unreachable
Doing a ping from the console of my server to the IP of the server, I get network unreachable.

An ifconfig eth0 returns no IP address.

Two questions:
1) What is the problem? NIC gone down?
2) How can I fix it? I'd prefer not to reboot the server as there is a session running with an active VM.

Any help gratefully received.

-- 2Hugh
 
Old 11-03-2010, 11:06 AM   #2
module0000
Member
 
Registered: Feb 2010
Location: USA
Distribution: RHEL
Posts: 36

Rep: Reputation: 15
What is the output of the command `ip link`, and `ip route`?

Also, check your /var/log/messages, it should contain some information about why the link went down.
 
Old 11-03-2010, 11:07 AM   #3
TB0ne
LQ Guru
 
Registered: Jul 2003
Location: Birmingham, Alabama
Distribution: SuSE, RedHat, Slack,CentOS
Posts: 18,811

Rep: Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190
Quote:
Originally Posted by 2Hugh View Post
Happily using VNCviewer to work on my RedHat server the other day, when suddenly, I lost contact.

The server is still up.
Retrying the connection via VNC I get a timeout.
Doing a ping from my client to the server IP, I get host unreachable
Doing a ping from the console of my server to the IP of the server, I get network unreachable.

An ifconfig eth0 returns no IP address.

Two questions:
1) What is the problem? NIC gone down?
2) How can I fix it? I'd prefer not to reboot the server as there is a session running with an active VM.
If you can't even ping it, that means either the server is down, or there's a network problem between your two machines. That network problem could be a downed line, bad switch/port, cable fell out, or someone did something with the routing tables/interfaces on the box.

You don't say what environment, but if you're doing this over a WAN, can you get to any other servers at that site, or at least ping them? If not, could be a telcom issue. If it's internal at your site, check the cabling, check the router/switch, and then get on the system console and check the interface ("ifconfig -a"), and make sure the IP address/netmask are correct. If so, can you get onto another machine on that same network, and ping the offending box? If so, the default route is probably wrong/gone. Do a "route" or "netstat -an", and verify.
 
Old 11-03-2010, 11:18 AM   #4
Davethesnake
LQ Newbie
 
Registered: Oct 2010
Posts: 25

Rep: Reputation: -14
yes hugh,the other lads know what there on about, t-bone for example .there are a few diagnostic options that should help you.
 
0 members found this post helpful.
Old 11-15-2010, 07:15 AM   #5
2Hugh
LQ Newbie
 
Registered: Sep 2010
Location: Guildford, UK
Distribution: Red Hat 4 update 5
Posts: 9

Original Poster
Rep: Reputation: 0
Thanks for the ideas. I don't know how to interpret the results of these commands as yet.

I executed these on the server via a console as root.

ip link gives:
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:19:b9:ea:92:3b brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
link/ether 00:19:b9:ea:92:3d brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
link/ether 00:10:18:28:6b:6c brd ff:ff:ff:ff:ff:ff
5: eth3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop qlen 1000
link/ether 00:10:18:28:6b:6e brd ff:ff:ff:ff:ff:ff
6: sit0: <NOARP> mtu 1480 qdisc noop
link/sit 0.0.0.0 brd 0.0.0.0

ip route gives:
172.20.16.0/20 dev eth0 proto kernel scope link src 172.20.16.139
169.254.0.0/16 dev eth0 scope link
 
Old 11-15-2010, 07:32 AM   #6
2Hugh
LQ Newbie
 
Registered: Sep 2010
Location: Guildford, UK
Distribution: Red Hat 4 update 5
Posts: 9

Original Poster
Rep: Reputation: 0
Question

Quote:
Originally Posted by TB0ne View Post
If you can't even ping it, that means either the server is down, or there's a network problem between your two machines. That network problem could be a downed line, bad switch/port, cable fell out, or someone did something with the routing tables/interfaces on the box.

You don't say what environment, but if you're doing this over a WAN, can you get to any other servers at that site, or at least ping them? If not, could be a telcom issue. If it's internal at your site, check the cabling, check the router/switch, and then get on the system console and check the interface ("ifconfig -a"), and make sure the IP address/netmask are correct. If so, can you get onto another machine on that same network, and ping the offending box? If so, the default route is probably wrong/gone. Do a "route" or "netstat -an", and verify.
Thanks for the ideas TB0ne.

The server is up, so network problem is in view.
I'm running a private LAN with one server up and running on it.

ifconfig -a for eth0 gives me:
Link encap:Ethernet HWaddr 00:19:B9:EA:92:3B
inet addr:172.20.16.139 Bcase:172.20.31.255 Mask:255.255.240.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:967 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 frame:0
collisions:0 txqueuelen:1000
RX bytes:104046 (101.k KiB) TX bytes:0 (0.0b)
Interrupt: 169 Memory:da000000-da011100

/etc/hosts includes the correct ip address for eth0 and suitable name.

/etc/sysconfig/network-scripts/ifcfg-eth0 has the HWaddr above, the ip address above, the mask above and the broadcase set as above for eth0.

doing a # route, gives:
Destination Gateway Genmask Flags Metric Ref Use Iface
172.20.16.0 * 255.255.240.0 U 0 0 0 eth0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth0

Does this help diagnose the problem.
 
Old 11-15-2010, 08:27 AM   #7
TB0ne
LQ Guru
 
Registered: Jul 2003
Location: Birmingham, Alabama
Distribution: SuSE, RedHat, Slack,CentOS
Posts: 18,811

Rep: Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190Reputation: 4190
Quote:
Originally Posted by 2Hugh View Post
Thanks for the ideas TB0ne.

The server is up, so network problem is in view.
I'm running a private LAN with one server up and running on it.

ifconfig -a for eth0 gives me:
Link encap:Ethernet HWaddr 00:19:B9:EA:92:3B
inet addr:172.20.16.139 Bcase:172.20.31.255 Mask:255.255.240.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:967 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 frame:0
collisions:0 txqueuelen:1000
RX bytes:104046 (101.k KiB) TX bytes:0 (0.0b)
Interrupt: 169 Memory:da000000-da011100

/etc/hosts includes the correct ip address for eth0 and suitable name.

/etc/sysconfig/network-scripts/ifcfg-eth0 has the HWaddr above, the ip address above, the mask above and the broadcase set as above for eth0.

doing a # route, gives:
Destination Gateway Genmask Flags Metric Ref Use Iface
172.20.16.0 * 255.255.240.0 U 0 0 0 eth0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth0

Does this help diagnose the problem.
Not really, since you don't say what box that information comes from. Again, if your local machine can get to the network, then you don't have a problem there. The problem is further upstream....check the routers/switches, and any other pieces of the connectivity puzzle. And again, can you get to any OTHER machine on the same network as the one you're trying to get to?

Also, it's been 12 days since your last post...have you been down that long?????
 
Old 11-15-2010, 08:28 AM   #8
2Hugh
LQ Newbie
 
Registered: Sep 2010
Location: Guildford, UK
Distribution: Red Hat 4 update 5
Posts: 9

Original Poster
Rep: Reputation: 0
Thanks for your help everyone. I decided to power cycle my server.

Now I can ping the box again.

-- 2hugh
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
Network Unreachable for Destination Network other than Interface Jack10 Linux - Networking 3 08-17-2010 07:50 AM
Linux network destination host unreachable linuxguy08 Linux - Server 1 07-22-2009 06:23 PM
Slow network connection, "Destination host unreachable" stefans Linux - Networking 2 11-22-2006 03:54 AM
destination network unreachable (Fc4 clean text installation )??? taiwf Fedora 3 10-31-2006 03:57 PM
Destination network unreachable questic Slackware 5 04-10-2006 07:11 PM


All times are GMT -5. The time now is 11:25 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration