Ping and Traceroute: Routing Loop Solved

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[tweetmeme]This is the first time I encountered this issue in real world. This happened when I deployed multiple sites that were connected through VPN in a hub and spoke topology. The main site has a leased line which terminates the VPN tunnel, mail and other hosted services. Also it has ADSL link which intended for web browsing. The other remote sites have ADSL lines which handles VPN and Internet traffic (e.g. web browsing).

During the deployment I encountered intermetent issues on the main site like couldn’t ping and browse some domains. What I did was to troubleshoot starting from the layer 1 up to layer 7 of the OSI model. I found out that it was on layer 3 as there was a routing loop. I’m sure you will ask how did I determine that it was a routing loop? I used the builtin network tools in my operating system which is the traceroute and ping. Traceroute basically shows us the route taken by packets across an IP network.For more information about Traceroute kindly visit this link.

You can also use ping to determine this issue. When there is a routing loop and you are using ping this error message will show “TTL expired in transit”.

I found out after troubleshooting that there was something wrong with the routing configuration. I double checked the configuration of the main site router and at the I couldn’t find any issues. Thus, I escalated it to the ISP and spoke to the technical team about this. They were hesitant at first as they were confident that nothing wrong from their side.

If you encountered the same issue kindly check your routing configuration of the router that you managed. If the issue isn’t solve call your ISP and explain to them the issue and troubleshooting steps performed. Take note that this might happen in local area network.

13 comments

  1. Thanks a lot for giving such a post, and I faced the similar problem in the production environment, this article helps me out of the problem.

  2. you talk a lot but say nothing,

    What was the exact issue/cause with the routing configuration? – what explanation did the ISP give? What did they do to resolve it, all you tell us is that they were hesitant??

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