Archives for the month of: March, 2013

On a recent Packet Pushers podcast, use of the Peer-Gateway feature on the Nexus 7000 and whether it resolves the lack of support for L3 over vPC was briefly discussed. The whole topic has been quite a big source of confusion, so let’s answer it straight away: using Peer-Gateway to try and resolve L3 over vPC issues is not supported, but more importantly in most cases it doesn’t actually work. The question is, why not? There are actually two reasons. Read the rest of this entry »

NX-OS release 5.2(1)N1(2) added support for storm control on Nexus 2000 NIFs / FEX Fabric Interfaces (this is also available on 6.0(2)N2(1) for the Nexus 6000) – these are the interfaces used to connect the parent Nexus 5500 or 6000 to the Fabric Extender. I looked into this feature recently for a customer so thought a quick overview might be useful as there are a couple of things to be aware of.

Firstly, the storm control percentage value that you configure gets implemented as a percentage of the total speed of the port-channel between 5K / 6K and FEX. Here’s an example:


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The requirement for layer 2 interconnect between data centre sites is very common these days. The pros and cons of doing L2 DCI have been discussed many times in other blogs / forums so I won’t revisit that here, however there are a number of technology options for achieving this, including EoMPLS, VPLS, back-to-back vPC and OTV. All of these technologies have their advantages and disadvantages, so the decision often comes down to factors such as scalability, skillset and platform choice.

Now that FabricPath is becoming more widely deployed, it is also starting to be considered by some as a potential L2 DCI technology. In theory, this looks like a good bet – easy configuration, no Spanning-Tree extended between sites, should be a no brainer, right? Of course, things are never that simple – let’s look at some things you need to consider if looking at FabricPath as a DCI solution. Read the rest of this entry »

The lack of support for running layer 3 routing protocols over vPC on the Nexus 7000 is well documented – less well known however is that the Nexus 5500 platform operates in a slightly different way which does actually allow layer 3 routing over vPC for unicast traffic. Some recent testing and subsequent discussions with one of my colleagues on this topic reminded me that there is still (somewhat understandably) a degree of confusion around this.

Let’s start with a reminder of what doesn’t work on the Nexus 7000:


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Virtual Port Channel (vPC) is a technology that has been around for a few years on the Nexus range of platforms. With the introduction of FabricPath, an enhanced version of vPC, known as vPC+ was released. At first glance, the two technologies look very similar, however there are a couple of differences between them which allows vPC+ to operate in a FabricPath environment. So for those of us deploying FabricPath, why can’t we just use regular vPC? Read the rest of this entry »