I know I said in my last blog post that I’d be discussing the OSI layer, but I left my documentation at work and I received a nice package in the mail yesterday: an AIR-LAP1142N-EK9.

1142NIt’s a fully capable 802.11n access point, both 2.4 Ghz and 5 Ghz capable, powered by either an external adapter or PoE. It came without adapter and with Lightweight Access Point (LAP) IOS on board, hence I got it rather cheap. Of course, I don’t have a Wireless LAN Controller (WLC) lying around that can configure a LAP. So I had to convert the IOS image to one of a standalone AP.

That proved difficult at first. The 1142N does have a console port, but after booting up it starts searching for a WLC and gets stuck in a loop: DHCP, searching WLC? releasing IP, DHCP, searching WLC,… So console access was not possible. On top of that, it didn’t reply to ARP requests, except for those originating from the subnet gateway (I suspect this is a security feature).

But, just as with Cisco switches, the 1142N LAP has a mode button, and if you hold it while it powers up, it will not load in any configuration or IOS but instead will fallback to IP 10.0.0.1/24 and query for a TFTP server, requesting a file named ‘c1140-k9w7-tar.default’ It does this by sending out broadcasts. I’ve set up a TFTP server in the same subnet (e.g. 10.0.0.10/24) and indeed it reacted… But nothing happened: still ARP information missing. So, after creating a static ARP entry of the 1142N on the TFTP server, TFTP started working! The 1142N retrieved the IOS, and after rebooting it showed as ‘LAP-1142N-EK9 running AP-1142N-E-K9 IOS’. It requested an IP address by DHCP again, after which it was accessible by telnet. Default username and password: Cisco/Cisco. After gaining telnet access, most things were similar to any other Cisco device: SSH key generation, line vty, interfaces,… After configuring it, it didn’t disappoint: throughput was around 95 Mbps, while it was connected on a 100 Mbps PoE switch, and at 20 meters and three walls, still 80 Mbps!

Advertisements