Friday, December 14, 2012

Ubiquiti Unifi POE

The Ubiquiti Unifi is a fairly cheap and straightforward managed WiFi solution if you are happy with a L2 bridging architecture with not too much additional stuff.
My biggest issue with the hardware is the non-standard POE implementation, which uses 24V "Ubiquiti POE".

Based on the datasheet and experience (, our base UAP devices can't directly use 802.3af POE, only the Pro UAP-Pro models can do that. Luckily, an official POE-adapter is sold by Ubiquiti (, and it's pretty cheap.

The 802.3af POE is 48V, but fear not: standard POE uses a detection mechanism before sending out the juice, so it won't fry your Unifi AP if you connect it directly to a POE switch, it just won't start up.

If you want to go with long cable runs, as higher voltage is better suited for longer runs, I'd suggest to use standard 48V POE to drive the cable, and use the Unifi adapter near the AP to convert it to 24V.

Thursday, December 6, 2012

Fun factsheet for Cisco 3500XL and 2900XL switches

It still seems like a popular topic, and these switches never really die, so here are some fun facts about them that I found to be useful (both from my experience and from the documentation):
  • These are layer 2 switches;
  • So they don't have DHCP snooping capabilities;
  • Nor any ARP inspection (DAI).
  • They can't do IP routing, or NAT.
  • Traffic distribution over an etherchannel can be based on source or destination MAC addresses, but not both. Distribution can be configured per etherchannel, not just system-wide. You can't distribute based on layer3-4 (IP,TCP/UDP) info.
  • No layer3 ACLs for switching. (Just for the control plane).
  • They have 2 hardware priority queues.
  • They only support L2 COS, not DSCP or TOS.
  • For IP phones, you have to go with a switchport trunk, encapsulation dot1q, nonegotiate, native vlan , allowed vlan ,, swichport voice vlan  type of setup.
  • The 3500XL and 2900XL use the same software, you can run 2900XL images on a 3500XL box.
  • The only members of the 2900XL family with Gigabit ports are the modular, 2U high chassis.
  • They do not support MSTP and GVRP.
  • They do not support LLDP.
  • The 2900 series does not support POE; but some 3500 series models do: look for the -PWR in the model name.
So far that's it, I might extend the list if something comes to mind.