Saturday, March 14, 2009

IE SP Vol 2 Lab 6 Continued

5.1 no issues
5.2 something in Dynamips crashed and I had to reload a couple of routers to get the 5-8 adjacency up.
5.3 no issues. Sham links are covered nicely on the doccd.
5.4 no issues.
5.5 no issues
5.6 no issues. I'm getting MUCH better with TE, this one only took me a few minutes.
5.7 this task was a major pain. I went ahead and made an assumption that only vlan78 was required. The first step was obvious, adjust bgp weights so the correct link was preferred. But it wasn't quite so simple. One of the PE routers refused to advertise the required routes. After way too much time troubleshooting, it turned out that this was due to sham-link costs. Adjusting these ensured the path through R5 was used.

The solutions guide just ignored the sham link altogether saying there was a conflict. It then went ahead and used an export map, which basically took the place of my weight adjustment. 6 one way a half dozen the other...

5.8 no issues

5.9 Yet another task that took a heck of a long time. The pings between ASs failed at first, naturally. It didn't take much time in debugging to determine that send-labels was required on the P-P bgp peers, since they were not running mpls with each other and did not split the vrf's out via subinterfaces. Next, I made sure the route-reflector left the next-hop-unchanged to allow the vpn traffic to flow PE-PE to ensure the vpn tag remained entact.

But no matter what I did, the upstream PE router was still seeing the bgp network as sending no label. I spent multiple hours troubleshooting this. Debug mpls packet is becoming my best friend.

So as it turns out, with a little help from the solutions guide, that the route-map is to blame. If a route map is used, set mpls-label must be configured in the route-map, otherwise this will override the send-label portion of the bgp neighbor config.

But even after I configured this, the CE router still couldn't ping AS54. After another hour or two troubleshooting, the problem seemed to be that the upstream P router was trying to send the traffic back via mpls instead of ip. I have no idea why this was happening, but a mpls encapulation failed message was occurring. Guessing that something may have just gotten hosed on the router in all my previous messing around, I gave up and just reloaded the upstream PE routers. Sure enough, everything came up upon the reload. Annoying, but it's working.

Too much time spent, but I think I got a lot of good troubleshooting experience.

5.10 Yet again more nastiness. The basic task was simple--summarize using an aggrigate address to ensure the longer-match prefix is preferred. An interesting trick. But for some reason, the path to R8 breaks once I set this. Tearing down the TE tunnel fixes it. So yet again i put a ton of time into troubleshooting this. It turns out that for some reason R1 is ignoring the sham-link when TE is operational.

A reboot of R1 seemed to take care of the sham-link issue, but my traffic is still not making it back to R8.

After another hour spent of troubleshooting, I'm giving up on this one. I'm going to write it off as some kind of weird incompatibility with sham-links and TE or something like that. Either that or something is still not clicking with TE that's not mentioned in the solutions guide either.

5.11 wow, no issues

5.12 of course, once again issues. This again deals with the sham link and R7 cannot be made to take the backdoor route to R8 to come into nat on R5 in the appropriate interface.


nwachonky said...

hello sir, i am currently studying for my ccip and i will like to know what materials that you used for your mpls studies during your ccip exams


also what materials can be used for lab practice too

Ed said...

The following post should answer your questions: