Archive for the ‘Cisco Nexus’ Category

Nexus (NX-OS) protocol support (and cleanup)

Monday, March 29th, 2010

Over the years, Cisco has been very instrumental in the design and standardization of many networking protocols.  There are lots of examples where a need for a protocol was identified and Cisco filled the need with a Cisco-proprietary protocol.  Cisco-proprietary can sound bad, but it really isn’t.  Let’s give them some credit here – network equipment vendors are in competition and don’t typically play well together.  Often times vendors pitch proprietary solutions in an attempt to carve out a niche that delineates them from their competitors.

There are several standards organizations in existence today (IEEE, IETF, CableLabs, etc.) which many vendors work with and closely follow.  While this sounds ideal (and is very beneficial), standards often take a significant amount of time to be ratified, leaving any current needs unaddressed from a standards perspective.  The only alternative (for a quick resolution) is a proprietary solution, while the standards process is given time to complete. (more…)

Missing VLANs are not automatically created in NX-OS

Wednesday, February 17th, 2010

In IOS, if we assign a switchport to a non-existent VLAN, the switch will kindly create the missing VLAN for us. NX-OS does not do that – if a switchport is assigned to a missing VLAN, the interface will be placed in the down state. Let’s look at it… (more…)

FEX configs are retained

Monday, February 15th, 2010

The N5k maintains the config of the FEXs, even when they’re removed (and even though it’s not visible to us). In this article, we’re going to look into this a little further… We’ll start with a working FEX, using Po100 (with Eth1/19-20 being the physical bundle members). (more…)

Some NX-OS features can’t be manually enabled

Wednesday, February 10th, 2010

The whole idea around features in NX-OS has been intriguing to me. It’s a good idea – I like it. It seems very similar to services on many other OSs (particularly *nix systems), however it doesn’t always strike me as having a rich feature set as of now.

For instance, the NX-OS config guides repeatedly refer to the show feature command to look at which features are enabled.  I’ve already mentioned that this command doesn’t exist today in older NX-OS versions – the currently-available NX-OS versions today support this feature (a reader confirmed this on the N7k and I’ve confirmed it on the N5k).  See this article for more info.  There are some interesting behaviors around features, in that some are manually enabled, while others are automatically enabled and disabled as needed.  Let’s dig into this a little deeper for an example… (more…)

EtherChannel behavior in NX-OS

Tuesday, February 9th, 2010

I’ve had a lot of discussions with clients about the behavior of Port-Channel interfaces and their associated physical counterparts.  It’s necessary for many parameters of the physical and logical interfaces to be the same.  Here’s the behavior within NX-OS and the preferred way that I make changes to EtherChannels.

In this, we’re going to continue working with the logical interface Po100 and the physical interfaces Eth1/19 and Eth1/20 which will be in the EtherChannel. (more…)

Why EtherChannels should be used for FEX interfaces

Monday, February 8th, 2010

I prefer to use port-channel interfaces for the fabric interfaces when connecting fabric extenders (FEXs). If a single interface in the bundle fails, it won’t remove the fabric extender interface – it simply reduces it’s bandwidth. This results in stable, predictable, redundant and resilient behavior. Let’s prove this point. (more…)

Experimenting with Static Pinning

Thursday, February 4th, 2010

What happens when more links are associated with an FEX than are permitted in the max-links parameter? Let’s find out…

(more…)

The FEX information is cached until it’s re-assigned to a different FEX

Tuesday, February 2nd, 2010

Continuing our journey into the world of FEXs on the Nexus 5000 and 2000, today we’re going to look at the behavior of the FEX configs themselves on the Nexus 5000.

All of the configuration and software information (firmware/images) for the FEX (Nexus 2148T) are kept on the parent switch (a Nexus 5000-series switch). Going on this, what happens when the FEX goes offline? Do I lose my config?

A stack of 3750 switches can be provisioned ahead of time, so that as stack members are added (assuming that they’re the correct type/model), no changes must be made – just move on. What kind of behavior is available on the Nexus 5000/2000?

I haven’t found provisioning available yet for FEXs on the N5k, however I did notice that the configurations for the FEX are retained when the FEX goes offline and online. This is great — if the 2148T fails or the fabric interface links are disconnected, the config will still be there (although not visible until the FEX comes back online). This article is looking at it from an association perspective (N2148T association with the N5k, not a configuration (actual port configs on the FEX). With that said, let’s explore this further… (more…)

What happens when the wrong serial number is entered for the FEX?

Sunday, January 31st, 2010

Continuing on the journey of FEXs on the Nexus platform, we’re exploring about serial numbers being statically bound to an FEX instance. It’s possible to allow any N2148T to connect to any FEX instance defined on a N5k. Simply plug in the N2k and off it goes.

This is a good low-maintenance approach, but what if I want to be more granular? What if I have several N2ks and I want to ensure that each N2k is plugged into the correct interfaces on the N5k? The only way to verify this is to tie a serial number to the FEX ID on the N5k, which will only allow that single N2k to come up on that FEX ID… or will it? What happens if the wrong serial number is entered?
(more…)

Methods for connecting FEXs

Friday, January 29th, 2010

If you’re wondering what an FEX is, check out this article: http://www.cciezone.com/?p=231.

FEXs are connected to the parent switch(es) via fabric interfaces.  These are 10Gbps interfaces which connect the two switches (think of a stacking cable on a 3750-series switch).

There are two methods of configuring fabric interfaces:

  • Static pinning
  • EtherChannels

Although these are somewhat differentiated in some of the documentation, the static pinning looks almost the same as that used for EtherChannels.  The main difference is that static pinning uses physical interfaces, whereas EtherChannel uses a single Port-Channel interface for the fabric interface (there are some minor configuration differences and requirements as shown below).

(more…)