How Can I Easily Tell If My Network Has Power Over Ethernet?

Question

How could I easily identify whether my network at my office is capable or is utilizing PoE? I have Cisco IP phones but I know some phones can operate entirely over ultra-low voltage. How could I look at my network set up and be able to identify if my network has PoE?

If it doesn't have/utilize PoE would it be easy to implement it?

Answer 1

Adding to what YLearn already said, show power inline is how you can quickly retrieve that information from the cli to see if your hardware supports it.

A non-PoE supported device would display the output below if it were available.

MHN00642AN01#show power inline

Module   Available     Used     Remaining
          (Watts)     (Watts)    (Watts)
------   ---------   --------   ---------
1             n/a        n/a         n/a
Interface Admin  Oper       Power   Device              Class Max
                            (Watts)
--------- ------ ---------- ------- ------------------- ----- ----
MHN00642AN01#

Versus a fully PoE capable system:

MHN00421AN01#show power inline
Available:124.0(w)  Used:0.0(w)  Remaining:124.0(w)

Interface Admin  Oper       Power   Device              Class Max
                            (Watts)
--------- ------ ---------- ------- ------------------- ----- ----
Fa0/1     auto   off        0.0     n/a                 n/a   15.4
Fa0/2     auto   off        0.0     n/a                 n/a   15.4
Fa0/3     auto   off        0.0     n/a                 n/a   15.4
Fa0/4     auto   off        0.0     n/a                 n/a   15.4
Fa0/5     auto   off        0.0     n/a                 n/a   15.4
Fa0/6     auto   off        0.0     n/a                 n/a   15.4
Fa0/7     auto   off        0.0     n/a                 n/a   15.4
Fa0/8     auto   off        0.0     n/a                 n/a   15.4
MHN00421AN01#

On a chassis style switch, it's even simpler. Just issuing the show power command gives detailed output of what your system can offer.

MHN00526CAN01#show power
Power                                             Fan      Inline
Supply  Model No          Type       Status       Sensor   Status
------  ----------------  ---------  -----------  -------  -------
PS1     PWR-C45-2800AC    AC 2800W   good         good     good
PS2     PWR-C45-2800AC    AC 2800W   good         good     good

Power supplies needed by system    : 1
Power supplies currently available : 2

Power Summary                      Maximum
 (in Watts)              Used     Available
----------------------   ----     ---------
System Power (12V)        856        1360
Inline Power (-50V)       182        1400
Backplane Power (3.3V)     40          40
----------------------   ----     ---------
Total                    1078        2800

MHN00526CAN01#

Answer 2

Some ways to check if you have PoE on the network:

• On a Cisco switch, log in and enter show power inline and if it supports PoE, you should get output showing which ports are drawing power, a summary of configuration, etc. Any managed PoE switch should have a similar command.
• Do a web search for your network equipment's model/line and see if it lists PoE as one of the features.
• Use a testing tool that checks for PoE, such as the Fluke LinkRunner AT.
• Check for "midspan" power injection devices. These can be on the switch side or the client side (or somewhere in between). The small form factor ones will have two network connections, a data in and a data/power out. Larger ones may have multiple pairs of data in and data/power out.

Since you mention Cisco VoIP phones, they need to be getting power from somewhere. The two options are PoE or a power supply. If they are using a power supply, then you probably don't have PoE (or at least enough power available on PoE). Neither allows you to connect a PoE device to the PC port to get power (there is no PoE pass through).

If you find you really need to daisy chain, then you may be able to use a product like the Cisco 700W AP. Haven't used them myself, but I know they have a PoE port in the switch ports they provide, so you could possibly plug the phone into the AP. However I do believe they require 802.3at power to do so.

The two pieces of equipment you list are a 2811 router and a 2950 switch. Most routers do not provide PoE, and to my knowledge, the 2811 is no exception to this. I also don't know of any 2950 series switches that have PoE, and based on the age of that product line, if there were any it would be the Cisco pre-standard proprietary flavor, not 802.3af or 802.3at.

As to how easy it is to implement if you don't have it, typically most places will either replace their older switch or add a new switch that supports PoE for their PoE devices. You will probably wish to have a new switch anyhow as the 2950s are all 10/100Mbps (with a couple exceptions that have two or transceiver capabilities) and even 802.11n wireless access points can exceed 100Mbps of throughput so 1000Mbps ports are nice to have.

If you don't want to go down the new switch route, then you can use midspan power injectors. These come in inexpensive non-managed versions as well as more expensive managed versions. The problem with most non-managed versions is that there is no way to remotely power cycle a non-responsive access point, someone will have to physically disconnect the cable.

In either case, some form of PoE will almost always be less expensive than running electricity to the AP location.