Latest LQ Deal: Linux Power User Bundle
Go Back > Forums > Linux Forums > Linux - Networking
User Name
Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.


  Search this Thread
Old 08-13-2010, 12:45 PM   #1
LQ Newbie
Registered: Aug 2010
Posts: 4

Rep: Reputation: 0
Question how to forward ip tunnel's output

I'm trying to implement a routing short-cut solution, whose requirement is as following:
server1(Linux) sends ip packets(destined to server3) to server2(Linux) via an ip tunnel between them, server2 forwards the ip tunnel's output (the inner ip packets) to server3. Each server has only one NIC and a public ip associated with it. All servers can communicate with each other.
I'm sure the ip tunnel between server1 and server2 was configured correctly and worked well. server2's ip_forward was enabled too. On server2, I can capture the traffic on the ip tunnel interface, and they are originated from server1 and destined to server3. The problem is server2 does not forward the ip tunnel's output at all.
On server2, I just run "echo 1 > /proc/sys/net/ipv4/ip_forward". Is there anything I missed for enabling ip_forward?
Or originally, ip forward can't work on servers with only one NIC, can it?
Any help would be greatly appreciated!
Thanks a lot!
Old 08-17-2010, 07:35 AM   #2
Registered: Sep 2007
Location: Poland
Distribution: Ubuntu LTS
Posts: 101
Blog Entries: 12

Rep: Reputation: 26
AFAIK ip_forward parameter has nothing to do with tunnelling, and you have to set up the tunnels properly.
It looks for me, that you have 2 servers (named server1 and server3), and one machine named server2, which in fact should act as a router. Your short-cut looks too much complicated
Old 08-18-2010, 01:23 AM   #3
LQ Newbie
Registered: Aug 2010
Posts: 4

Original Poster
Rep: Reputation: 0

Yes, ip tunnel should not impact on ip forward. But what I see is ip tunnel's output (the inner ip) is not be forwarded on my ubuntu server. According to ip tunnel's implementation, the inner ip should be put back to recieve queue -- netif_rx(), then if its destination is not the local host, ip forward should forward it again. Is it right?
I'm not sure if there's completely no problem with my configuration of ip tunnel, but on server2's tunnel interface I can capture the traffic from server1 to server3.
I'm not sure if this only occurs on ubuntu too. I want to switch to another Linux distribution to try it.
Old 08-18-2010, 05:34 AM   #4
LQ Newbie
Registered: Aug 2010
Posts: 4

Original Poster
Rep: Reputation: 0

I try fedora with server2, then it works. So seems there's a bug in ubuntu. I have reported a bug to ubuntu community:

Hope they can respond it quickly!


forward, ip, tunnel

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
forward, input & output chains on iptables kurrupt Linux - Software 4 11-09-2011 04:29 AM
can not forward X11 output Hewson Linux - Software 7 09-02-2008 10:39 AM
Mangle Output vs. Forward Palula Linux - Networking 1 04-12-2008 03:19 AM
How do I forward standard and error output into same file? ivj Linux - Software 5 07-19-2005 08:30 PM
Using echo to output a string to a file with forward slashs chrisk5527 Linux - General 15 06-21-2003 02:04 PM > Forums > Linux Forums > Linux - Networking

All times are GMT -5. The time now is 05:37 AM.

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