Archive for the ‘Routing&Switching’ Category

Supervisor Upgrade

Tuesday, February 17th, 2009

This past week, I upgraded one of our Sup-720s to the new Vs-720 which supports VSS (virtual switching system). I’m not using VSS at this time, but we will in the near future. We are only using a single Supervisor in each of our distribution switches. I did some work in the lab to make sure the supervisor upgrade would be as quick and painless as possible. Our access switches are all dual homed to another distribution so the impact would typically be minimal.

Here is what I did for the supervisor upgrade ::

I had the new supervisor running in a lab switch for a few weeks. Our production switches are fully loaded 6513 switches and what I was using in the lab was 6506 switches.

1. Let Supervisor burn in for 2-4 weeks in a lab.
2. Backup current config of production supervisor (this will be used to prep the new supervisor). Also record output of “show ip inter brief”
3. Establish base config for new supervisor.


Clean up those SPANs

Monday, February 9th, 2009

We recently started an eval with a product from NetQoS called SuperAgent. Basically, this device passively monitors application performance. It sits off a span or mirror port on the network. We are also using a product called Gigastor which feeds mirrored traffic to SuperAgent as well.

One thing to remember about SPAN configurations is that you have to be very selective about what you are spanning, because mirror ports can be quickly overwhelmed. A lot of times you know what servers you want to mirror traffic from, so you just span all of those source ports or even worse an entire source vlan.

The other thing to keep in mind is that you need to span in such a way to prevent duplicate packets if possible. If you start blindly mirroring all your servers, you may find yourself with duplicate packets which can throw off your packet loss and retransmission delay metrics. You have to remember that when mirrored servers talk to each other, you will certainly end up with duplicates. If you have a multi-tiered application where you have front-end servers talking to back-end, you definitely want to clean up those SPANs!

The most common method of traffic mirroring is using SPAN or RSPAN with Cisco switches. Using a network tap is also a very good method as well.

Here is an example of a scenario where you need to take care in what ports you choose to mirror.

Two Tier


Wake on LAN is actually useful

Wednesday, February 4th, 2009

I have to admit that I have heard about Wake on Lan since first starting working with PCs but I never had a use for it. I just never saw a need to have to wake a PC up that I was wanting to use…

If you’re like me, you like to keep your home PC off when you’re not home (I use sleep mode in Vista). I don’t see any reason to leave my PC up and running all day if I’m not there using it, plus it saves on electricity.

In my case, I wanted to be able to RDP to my home PC from anywhere, but I didn’t want to have to leave it running all day.

Here’s how ::

1. First enable Wake on Lan on your PC Nic in Windows (you may have to enable in BIOS too).

wake on LAN pc


Routing Challenge

Thursday, January 29th, 2009

I was dealing with an issue the other day at work that was kind of challenging and made my brain hurt…


Note the diagram below.

Before Network

What we have is a simplified diagram of 4 routers. Rtr A and B are currently connected to our global ATT MPLS carrier and receiving routes via BGP from our other corporate BGP sites (expected). Rtr A and B are also advertising their own networks back out providing reachability to subnets behind Rtr A and B as well as C and D. End-to-end connectivity is easily done with the bidirectional exchange of route information — that is not the challenge here.


Cisco Telepresence QoS

Monday, January 12th, 2009

Recently we added another Cisco Telepresence in our network (CTS 3000) and it gave me an opportunity to work on some QoS configs.

Cisco has a great reference for QoS with Telepresence and is a must read for anyone deploying Telepresence on the network.

Cisco Telepresence SRND

I dealt with the QoS config in 3 different levels :: access, distribution, and WAN edge

At our access level, we use Catalyst OS and IOS in distribution and WAN edge. Refer to the SRND for the recommended values depending on Line cards being used. The example below is for 1p3q8t cards. To find out the QoS capabilities of the port use “show qos info runtime mod/port”.

Access config ::