Nexus 7000 Virtual Portchannel Part 3 (final)

April 30th, 2009

Ok guys, sorry for the delay on this one… Between work and my personal life, I have been so busy!

At this point, we have a working vPC peer link between our Nexus boxes. Remember our vPC peer keep-alive link needs to be up as part of this (I think of it as the heartbeat link).

So now we need to connect the access switch to the Nexus 7000 boxes to take advantage of virtual port channels. Let’s take a look again at our diagram.


In this example, I’m using one of the newer 4948 TenGigabit switches. There are two TenGigabit ports on the 4948. I’m connecting one to “Nexus1” and the other to “Nexus2”. This doesn’t have to be 10Gigabit, it could be any number of 1gig ports if you like. For example, you could connect 4 gig ports to Nexus1 and 4 gig ports to Nexus2. Remember, you can have up to 8 active ports in a port channel.

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Q&A – VSS and Jumbo Frames

April 28th, 2009


I currently have a new blade chassis connected to my Nexus 5020 which has a Mulitchassis Etherchannel to a pair of 6509s running VSS. The blade system is using HP Flex 10 cards*. My first issue that I ran into was that I had to enable Jumbo MTUs on the Nexus. The reason being is the HP Flex 10 cards where sending jumbo frames which were getting dropped 🙁 I also had to enable Jumbo Frames on the the trunk ports as well as the ethernet ports on the VSS that connect back to the Nexus since there will be some inter-vlan routing going on. I guess I should enable jumbomtu on the layer 3 interfaces as well now that I think about it.

Do I also need to enable system jumbomtu on the VSS? What about the VSL links? The reason I ask is that when I run the command “show interface counter errors” I see giant frame errors on the VSL links as well as FCS errors. However, I cannot adjust the MTU size on the VSL links or the port channels since they are not switchports. Can I make the VSL links switchports or will VSS not allow this? I guess I’m a bit confused on the whole jumbomtu thing. Once you start to enable it where do you stop.

Thanks for the help,

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Nexus 7000 Virtual Portchannel Part 2

March 30th, 2009

Wow, last week I was swamped preparing for a domestic MPLS migration in India (more on that later). I wanted to post this sooner…

In Part 1 of configuring virtual port channels on the Nexus, I talked about what may be needed to enable the vpc feature. Here’s a continuation of the process.

Between your two nexus boxes, you’re going to have a vpc peer link and a vpc peer keep-alive link. Without the keep-alive link, your vpc peer link wont come up.

Cisco vpc config guide

See Diagram


! Again, the first thing you want to do is enable vpc

Nexus1(config)# feature vpc

The vpc peer link between switches is going to be your traditional layer 2 trunk. There are some other minor configurations you will need regarding your vpc peer link.

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Nexus 7000 Virtual Portchannel Part 1

March 16th, 2009

This past week, I configured our 2 Nexus 7000 boxes to take advantage of the new Virtual Portchannel (vPC) feature.

Here’s some info on this feature ::

Config Guide

If you read my article about VSS technology, then the benefits with virtual portchannels are pretty much the same. One major difference is that the two Nexus boxes are still very much separate unlike using VSS. You still no longer need to worry about Spanning-tree. One thing that wont change from how you are probably doing things today is the HSRP configuration. You will still have your active and standby HSRP devices. The trick here is that when you dual home to the distribution, you use only one portchannel at the access side. Your access switch will dynamically load balance across both links using standard portchannel load balancing algorithms. The thing to remember is that packets received by the standby HSRP device are actually forwarded. So in a sense, you have a “active-active” HSRP state in the background.

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Book Review – CCENT Network Simulator

March 13th, 2009

CCENT network simulator


Well, the days of using the Boson network simulator for your CCNA studies is over (thankfully!). I have used simulators quite often over the years and have had mixed feelings about them. I think the new CCENT network simulator will surprise a lot of people out there with mixed feelings about using simulators. You have to remember that simulators are scripted and pretty linear so don’t expect to be able to configure your own network scenarios and use any IOS command you can think of. The purpose of this simulator is to provide hands-on practice being able to master all the objectives on the CCNA exam. It simply runs from your PC once installed.

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