Cisco 3524XL DHCP acting strange: spanning tree?

By robo_dev ·
The Cisco switch is connected to a generic 2Wire DHCP server. Everything works great, except....

I am installing some Ademco 8132 alarm keypads that are basically single-board computers that use DHCP. When plugged into the Cisco switch, they get no address.

Plug them into anything else, and they're happy as a clam.

For example, if I plug a my trusty netgear four port switch into a port on the Cisco, and plug the keypads into the netgear switch,the devices get an IP just fine that way. So DHCP is working...somehow the Cisco is having some heartburn at layer 2??

Are there any magic Cisco settings to look at?

The Cisco is set to factory defaults, so there is only one VLAN. I believe Spanning Tree is turned on by default.

Do I maybe need to disable spanning tree? (the network topology is flat). Any other weird settings to fiddle with?

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console in to the 3524

by CG IT In reply to Cisco 3524XL DHCP acting ...

does anything pop up ? speed and duplex problems will show up on the console as a mismatch. With a mismatch there's no communications.

one would think the devices would autonegotiate the speed and duplex, but sometimes this doesn't happen on Cisco switches. I've got a 2950 that doesn't autonegotiate with a 10baseT NIC so while the port is up, no traffic.

and is this a pwr model 3524?

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Good thought

by robo_dev In reply to console in to the 3524

these keypads are vintage 2004 and I bet they are 10mb devices. I will try nailing the ports up at 10 half, or full, or whatever it takes.

Too bad they cannot use power over ethernet, as I need to install a separate 12V PSU for these gizmos....

Ever seen a device that could use power-over-ethernet in a non-standard way?

It would be great if I could power my IP-based security cameras from the switch, but it seems that only phones and wireless access points use POE.

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you will know if it's a speed/duplex problem

by CG IT In reply to Good thought

if you console in. the switch will put a message in the console session that there's a mismatch, what mismatch there is and on what port the mismatch is on.

then you set speed and duplex on that port. Copy the config to start and your set. Just don't switch the host to other ports.

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Powered patch panel

by NetMan1958 In reply to Good thought

They do make powered patch panels that will apply the power to the correct wires and not damage the switch.

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by robo_dev In reply to Powered patch panel

Since my Cisco switch is plugged into a UPS, and you can control the power to each port remotely, it would be cool if you could power an IP camera, or even a low-power PC (NetPC) using just a plain old ethernet cable.

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yeah but isn't the 3500s putting out 48V for the phones

by CG IT In reply to Powered patch panel

well you just answered that question i guess.... you can set voltage per switchport?

not up on 3500 poe switches...

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and since were talking ip phones you guys ever do AA with CME?

by CG IT In reply to yeah but isn't the 3500s ...

damn if I can get AA service to work on CME 4.1

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Nope still stuck in the dark ages of the old-school PBX

by robo_dev In reply to and since were talking ip ...
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well there's always the trixbox

by CG IT In reply to Nope still stuck in the d ...

and SIP/SCCP phones...

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by robo_dev In reply to yeah but isn't the 3500s ...

Actually it looks like POE is used for security cameras. But most of my cameras run at 12V and POE is between 37-57 Volts (zap).

Also, the power is not 'just there', it takes a plugged-in 802.3af-aware device to wake it up.

(below from wiki)

Cisco's original PoE equipment was manufactured many years before there was an IEEE standard for delivering PoE. Cisco's original PoE equipment was capable of delivering up to 10 W per port. The amount of power to be delivered is negotiated between the endpoint and the Cisco switch based on a power value that was added to the Cisco proprietary Cisco Discovery Protocol (CDP). CDP is also responsible for dynamically communicating the Voice VLAN value from the Cisco switch to the Cisco IP Phone.

The PSE (switch) will send a Fast Link Pulse (FLP) on the transmit pair. The PD (device) connects the transmit line to the receive line via an low pass filter. And thus the PSE gets the FLP in return. And a common mode current between pair 1 and 2 will be provided resulting in 48 V DC[15] and 6.3 W[16] default of allocated power. The PD has then to provide Ethernet link within 5 seconds to the auto-negotiation mode switch port. A later CDP message with a type-length-value tells the PSE its final power requirement. A discontinued link pulses shuts down power.[17]

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