Mar 11

IP Phone may have power, but it doesn’t mean it’s connected to the network.

Last week I had one of the phone techs come to my desk and ask me to check the configuration on a switch port. He was setting up an IP Phone for a user at a new desk and the phone powered on but would not register with Call Manager. I checked the switch port, the configuration was correct, but the port was down. To double check the port, I went to the closet with the tech to make sure we were looking at the correct port. After confirming we were looking at the correct port, we headed to the desk.

When I arrived at the desk, the IP Phone had lights illuminated with an error of “Network Not Available”. I suggested that the tech replace the CAT5 jumper at the desk to see if that would resolve the issue, it did. With a new patch cable, the IP Phone powered up and registered with Call Manager.


So why did a new CAT5 patch cable fix the problem?

CAT5 has 4 pair of wires inside of it. 10/100 Ethernet uses pins 1,2,3,6 Ethernet (Data). Power Over Ethernet (PoE) uses pins 4,5,7,8 to power the end device.

In this case, the IP Phone used 100BASE-T, so one or more of pins 1,2,3 or 6 were damaged while 4,5,7 and 8 worked fine.

The troubleshooting steps that the tech went through were correct.
– Phone powered up, but wouldn’t register.
– Switch port was enabled, but didn’t look configured
– Switch port was configured correctly.
– Had to be a cable issue, or a phone issue

By understanding how the basics of PoE worked, I was able to easily identify the best action to troubleshoot the issue. After confirming the configuration was correct, I was able to easily troubleshoot the issue.

Understanding the basic foundations of the technology that you use can really reduce the time it takes to troubleshoot. There are many resources on how PoE works, here is the resource I used to identify what pins are used in the CAT5 cable for PoE. There is a nice chart towards the bottom of the page.

Have you run into this PoE issue on a PoE device?
Do you have any good stories to share about a co-worker not understanding the basics of a technology they are using?

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Feb 25

QOS on the 4500-E with IOS XE is different from the older 4500s.

For years I have configured QOS on Cisco switches. The 4500’s and 6500’s always caused me the most frustration. Depending on the line card, you may have 2 or 4 hardware queues with the Priority queue different on each platform. The 4500’s and 6500’s are different then the other Cisco platforms.

I recently had the privilege to setup a new 4506-E running IOS-XE 3.3.0X0(15.1(1)XO). For the most part, this switch was very similar to the older 4500’s. Most of my configuration from the other 4500’s easily pasted into the switch. I was doing well until I got to the QOS portion of the config. I found that with the exception of the Marking policy, nothing else worked.

What did not work?
1. Trust DSCP commands on the uplink ports
2. Egress queueing, mapping COS value to the hardware queue
3. COS To DSCP mapping
4. Selecting the priority queue, what queue was the priority queue?

After some more digging I found out that the 4500 trust DSCP and COS values by default. This explains why the commands would not work. This in itself may cause new challenges to you. If you are not careful, an end user or application could put all of their traffic in the EF queue and use up all of your priority bandwidth. To resolve this challenge, I mark all traffic coming in from an edge port. How do you handle this?

Egress queuing, this is done with a policy map just like a router. The switch comes with 8 hardware queues. (I’m very happy to hear that Cisco finally added 8 hardware queues per port on their switches. Other vendors have been doing this for years.) In your policy map you identify what queue you want to be the priority queue, then under each class you can specify the bandwidth you want to give that queue. For more information on how to configure the policy map, please refer to the Cisco IOS XE Documentation You do need to be careful while going through this guide. The IOS XE software works on routers too. You may find documentation that only applies to ASR routers, but does not work on the 4500 platform.

COS to DSCP mappings may not be needed. I mark all of my traffic at the edge port with DSCP values. I mark DSCP so I do not need to worry about the COS value being dropped going over an access port. With IOS XE, the outbound queuing policy is capable of queuing egress traffic by DSCP value. Due to this, I don’t have to worry about the COS to DSCP or DSCP to COS mappings.

Now for the priority queue and mapping QOS markings to a hardware queue. This has been a major frustration for me due to the different capabilities and commands on the variety of Cisco platforms. To me, this has been no different then if every platform was a different vendors equipment. Due to the challenges in the past, I was really getting upset when I wasn’t able to find any documentation on how to perform this mapping. After speaking with my Cisco SE, I found out that IOS XE will automatically place the different classes in your policy map into different hardware queues. The specific queue for the priority traffic is GONE!!! The unique commands of allocating QOS markings to hardware queue is GONE!!!

Even though this new IOS was frustrating at first, I believe the changes in IOS regarding QOS is a drastic improvement. The old method was more difficult then I feel it should be. As long as you understand Cisco’s MQC logic, the change in Trust and automatic queuing methods, I believe you will find this IOS much better to work with. Do you agree?

Other then Marking and queuing, what other changes have you notices in this new version of software?
Are you happy with the newer IOS XE on the 4500?