After working with MPLS Traffic Engineering lab for a few days and interpreting IP addresses from various traceroute outputs, I finally had enough and wrote a simple Perl script (below) that parses router configurations and produces ip host configuration commands for every interface IP address it encounters. When you paste the ip host commands into the configuration of the edge router from which you do the tests, the meaningless numbers finally make sense.

An anonymous commenter to my implicit NULL/PHP post made a very valid point:

Most Cisco documentation states that you must enable LDP before doing MPLS-TE, which is a complete fallacy.

If you're using MPLS TE simply to shift IP traffic around your network, he's absolutely right: there is no need to run LDP if you have an IP-only network. If you're running MPLS VPN or BGP on edges/MPLS in the core, the answer becomes “it depends.”

I documented the detailed rules and undesired side effects if you ignore them a long while ago, but that article disappeared into /dev/null. Fortunately archive.org caught a copy before that.

Would you like me to migrate that article to ipSpace.net? Send me a message and I just might do it...

 

This article is part of You've asked for it series.

I've always believed that you need to teach your students (more so if they are engineers) how things work, so they'll be able to understand why they do things they way they do them. It seems to me, though, that the training courses I'm seeing veer ever more toward overviews and recipes ... but there are a few things you can do on your own.

• Jeremy Stretch started writing about BGP aggregation. So far he's covered the principles and the route suppression options. Unfortunately, my question still remains unanswered: why would you use these tweaks in a well-designed network?
• Anthony Sequeira started to explain the QoS mechanisms on PIX/ASA. So far he's covered the overview, modular framework, priority queuing and traffic shaping. Now we're waiting for part 5 of another trilogy in four parts.
• Joe Harris was bored during the meetings (his words, not mine) and preferred to focus on IOS configuration lock and Configuration Generation Performance Enhancement. Now we know why some people @ Cisco hate Dynamips: SEs have found yet another way to survive the boring meetings :).
• Greg Ferro described how TCP SYN cookies work and provided interesting insight into the brain maps of network- and server engineers, which is the first post you should read if you're depressed by the cloudy and cold autumn weather.
  

End-to-end troubleshooting of MPLS VPN solutions is one of the more complex network troubleshooting tasks. On top of several sophisticated technologies and protocols used in MPLS VPN solutions, we have to deal with customer-to-provider interaction on the IP routing protocol level, which makes the troubleshooting efforts even more convoluted.

To minimize the impact of your customers on your troubleshooting efforts, you might want to start with the PE-to-PE troubleshooting. When used as the first step in your troubleshooting process, the PE-PE tests will bypass customer errors, intra-site customer routing problems, PE-CE interactions, and route redistribution issues.

In one of the MPLS-related posts, I’ve described the role of implicit NULL in penultimate hop popping (PHP). To make the distinction between implicit and explicit NULL even clearer, I’ve prepared a short explanation with corresponding diagrams.

The RFC 3101 (OSPF NSSA Option) states:

In addition, an NSSA border router should originate a default LSA (IP network is 0.0.0.0/0) into the NSSA. Default routes are necessary because NSSAs do not receive full routing information and must have a default route in order to route to AS-external destinations.

I am pretty sure IOS inserted the type-7 default route into an NSSA area when the NSSA feature was introduced.

If you’ve ever had the “privilege” of buying equipment from a large systems integrator (or directly from a large vendor), you’re probably familiar with this process: