Archive for the ‘CCIE SP’ Category


Cisco and their inconsistencies

January 30, 2012

Cisco is known for the inconsistencies between platforms and different IOS versions. I came across another that was rather annoying. Now between linecards.

Trying to configuring the following standard sub-interface Ethernet AToM tunnel on a Cisco 7606 with a ES+ linecard:

pseudowire-class CISCO
 encapsulation mpls
interface Te2/2.2
 encapsulation dot1Q 2
 no ip redirects
 no ip directed-broadcast
 no ip proxy-arp
 xconnect 12345 encap mpls pw-class CISCO

Yields the following misleading error…

7606(config)#int te2/2.2
7606(config-subif)# xconnect 12345 encap mpls pw-class CISCO
MPLS encap is not supported on this circuit

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Terminal Server in Dynamips

September 28, 2010

I find using a terminal server to connect to routers while labbing very efficient. I personally don’t like having 10 windows open when configuring devices. I tried it back when I started studying for my R&S but found I made more errors than worth. Since then I have gotten used to jumping between terminal sessions on one screen.

Like most I used Dynamips when I studied for the SP. I built a quad-core PC at home with Ubuntu. My laptop at the time was running Windows XP, but during my 4 months trial I got a Mac Book Pro. Obviously I had to study whenever I had time regardless of the platform. So I configured the same setup across all three platforms.

Configuring a terminal server in Dynamips requires a real interface to be bridged to a virtual router interface. This is done by using a loopback interface. This is done very differently on the three  platforms:

  • Windows XP (32-bit)
  • Ubuntu 9.10 (64-bit)
  • Snow Leopard 10.6 (32/64-bit)

The .NET file I used for the Internetwork Expert SP labs are at the bottom of the article.

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VRF-lite route leaking

September 13, 2010

The purpose of VRF-lite is to extend the logical separation of two different networks from a MPLS network down to a single CE router, connected to both these networks. It’s called VRF-lite because it is done without running MPLS (LDP/TDP) or MP-BGP between the PE and CE. Traffic is mapped to the VRF assigned to the ingress interface on the CE router.

But VRF-lite could be used without connecting to a MPLS network entirely! Consider what a VRF is?

A VRF is a mechanism used to provide logical separation between routing tables on the same router. It is locally significant to the router. Each interface on a router can only be assigned to one VRF, but a VRF can have multiple interfaces.

So VRF-lite could be used to separate multiple networks using the same equipment. (Not exactly something you should ever plan in a design, but it could be useful to know)

Once you have the separation you needed, you might need a way to selectively bridge that separation to allow communication between the VRF’s.

Assume the following scenario:
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Output101- sh run vrf

September 4, 2010

Now that the hard work is behind me, the awesome holiday has past, I can finally get back to all the outstanding fun stuff. That said I have some good half completed posts are on the way :)

I came across the following command browsing the DOC-CD a couple months back, and I have used it ever since.

sh run vrf [vrf-name]

The show running vrf feature provides the option to display a subset of the running configuration on a router that is linked to a VRF instance. It can be used to display the configuration of a specific VRF or of all VRFs configured on a router. The command is unfortunately only available on the more recent IOS versions, but if available makes life easy.

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