Why do AP's need IP addresses?

Roy_M · 03-07-2007

Hi,

I have a question about the physical structure of an AP. Other than network management considerations, does the IP address in an AP do anything.

As far as I am aware, an AP looks like the attached picture: one Ethernet interface, one 802.11 radio and a bridge used to join the two interfaces at layer 2. The IP address is put on the bridged interface which means that it can be accessed from the wireless interface or the Ethernet interface.

If we consider what happens when a wireless station transmits a frame to an AP, the AP is completely oblivious to all layer three properties of the transmission. Only the router/default-gateway in the wired network will look at the destination IP address of a packet.

So, returning to the original question: is there any reason that an AP has an IP address other than for management to-and-from the AP.

Cheers

ccie4526 · 03-07-2007

Quote:

Originally Posted by Roy_M

So, returning to the original question: is there any reason that an AP has an IP address other than for management to-and-from the AP.

You said it right there. Management. How else you going to get into the unit remotely and change power output levels, channel assignments, etc., etc.?

Roy_M · 03-08-2007

I thought so.

However, for some reason I have an image in my head of a configuration screen on a Cisco 1200 where they specify a subnet mask of 255.255.255.224. Maybe I'm imagining things.

Thanks for the reply ccie4526

BTW: Are you really a CCIE?

MikeP928 · 03-08-2007

Quote:

Originally Posted by Roy_M

I thought so.

However, for some reason I have an image in my head of a configuration screen on a Cisco 1200 where they specify a subnet mask of 255.255.255.224. Maybe I'm imagining things.

Thanks for the reply ccie4526

BTW: Are you really a CCIE?

That could well be a legitimate mask if the ap's is being isolated from the rest of the network via a router.I'm too lazy to figure up how many host addresses that would be.

He probably is a CCIE, and I bet his cert # is 4526.

MikeP

Airstreamer · 03-08-2007

http://www.wildpackets.com/products/...ities/overview

ccie4526 · 03-08-2007

Quote:

Originally Posted by MikeP928

That could well be a legitimate mask if the ap's is being isolated from the rest of the network via a router.I'm too lazy to figure up how many host addresses that would be.

Correct, 255.255.255.224 is /27 mask, gives 32 total addresses in the network range. Less two for network number and broadcast, less one for router, yields 29 available addresses in the subnet for hosts.

Quote:

Originally Posted by Roy_M

BTW: Are you really a CCIE?

Quote:

Originally Posted by MikeP928

He probably is a CCIE, and I bet his cert # is 4526.

I would be in severe violations of the copyright and trademark laws if I were advertising myself as something I were not. Ergo, you may safely assume that I am IE # 4526. Passed the practical in San Jose in March of '99, right before they added ATM to the test. Due for my recert here in a couple weeks, even.

Quote:

Originally Posted by Roy_M

However, for some reason I have an image in my head of a configuration screen on a Cisco 1200 where they specify a subnet mask of 255.255.255.224.

AP1200s factory default to an address of 10.0.0.1 with a /27 netmask. Thus what you have in mind is correct. Once you change that, however, all bets are off.

Roy_M · 03-09-2007

Quote:

Originally Posted by ccie4526

Correct, 255.255.255.224 is /27 mask, gives 32 total addresses in the network range. Less two for network number and broadcast, less one for router, yields 29 available addresses in the subnet for hosts.

Host portion

Quote:

Originally Posted by ccie4526

I would be in severe violations of the copyright and trademark laws if I were advertising myself as something I were not. Ergo, you may safely assume that I am IE # 4526. Passed the practical in San Jose in March of '99, right before they added ATM to the test. Due for my recert here in a couple weeks, even.

Best of luck with the exam. I hear it's about has hard as exams get.

Quote:

Originally Posted by ccie4526

AP1200s factory default to an address of 10.0.0.1 with a /27 netmask. Thus what you have in mind is correct. Once you change that, however, all bets are off.

Yeah I think thats what I was thinking of. Maybe it is Cisco's way of saying "Dont use too many APs in a broadcast segment"

03-08-2007	#5 (permalink)
Airstreamer Sniffin' the aether Join Date: Nov 2004 Location: A little North of Reason Posts: 2,821	Subnet Calc and some other FREE goodies! http://www.wildpackets.com/products/...ities/overview __________________ "America is at that awkward stage. It's too late to work within the system, but too early to shoot the bastards.." - Claire Wolfe, 101 Things to Do 'Til the Revolution

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03-08-2007	#3 (permalink)
Roy_M Registered Member Join Date: Jun 2005 Posts: 72	I thought so. However, for some reason I have an image in my head of a configuration screen on a Cisco 1200 where they specify a subnet mask of 255.255.255.224. Maybe I'm imagining things. Thanks for the reply ccie4526 BTW: Are you really a CCIE?