[SOLVED] Consecutive MAC addresses for the same device?

Louis_Carole · 10-21-2012, 08:16 PM

Dear All,

I'm learning about many many networking topics so I can "do proxy ARP."

My router, here named sinai, reports its MAC address as xx:xx:xx:xx:xx:F8 on its HTML status page.
My wireless adapter (wlan0) reports its access point's MAC address as xx:xx:xx:xx:xx:F9 using `iwconfig`.
The ARP cache reports that the MAC address of IP 192.168.10.1 is xx:xx:xx:xx:xx:F7.

If sinai has IP address 192.168.10.1 and is serving as wlan0's access point, then why does it have 3 distinct (and consecutive) MAC addresses?

- Louis

PS My guess is it either has something to do with routers having multiple NICs, or with somebody lying to someone.
PPS I haven't learned where the handle to the ARP toilet is yet, or I'd flush before asking this question.

Code:

schmo@mitzvah:~$ date ; iwconfig wlan0 ; arp -a
Sun Oct 21 20:32:53 EDT 2012
wlan0     IEEE 802.11bg  ESSID:"sinai"  
          Mode:Managed  Frequency:2.5 GHz  Access Point: 21:AB:B5:23:35:F9
          Bit Rate=54 Mb/s   Tx-Power=20 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=61/70  Signal level=-49 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:805  Invalid misc:110   Missed beacon:0

? (192.168.10.1) at 21:ab:b5:23:35:f7 [ether] on wlan0

HTML Router Status Page:

Code:

Current Time: Sun, 21 Oct 2012 17:32:58
MAC Address:  21:AB:B5:23:35:F8
Router Name:  sinai

wildwizard · 10-22-2012, 02:33 AM

So you have these interfaces (most likely) :-

1. Ethernet
2. WAN port
3. WiFi

Each physical interface needs it's own ARP address as at the network layer these are the addresses that are used to send the packets.

If your curious as to why your WiFi router has them in order like that then you should look at how they are assigned :-
The first half belongs to an equipment manufacturer and they allocate the second half as they produce equipment so a single device with multiple interfaces will normally have sequential ARP addresses.

Louis_Carole · 10-22-2012, 03:33 AM

Danke, WWiz.

The three MAC addresses correspond to separate NICs in my wireless router, sinai. I'll buy that, since that's how the MAC bureaucrats alot things in the best of times.

xx:xx:xx:xx:xx:F8 is the sinai-to-internet T-10 port?
xx:xx:xx:xx:xx:F9 is the sinai-to-wlan0 WiFi port?
xx:xx:xx:xx:xx:F7 is the sinai-to... ???

My eth0 is currently out of the picture - it's there on-board if need be, but is not configured or physically plugged in. There are no wires involved on the lee-side of sinai.

Does this mean that the access-pointness of a wifi connection is separate from its etherness, commanding 2 NICs for one WiFi connection? The MAC of wlan0 itself is from a different manufacturer.

wildwizard · 10-22-2012, 03:47 AM

It depends on how they put the thing together.

Yours looks like they integrated a modem/router device with a wireless AP connected internally via ethernet, this is why you can see 2 ARP addresses via that interface.

This is typical cheap manufacturing, you have a chip that does Y and one that does X but putting chip X and chip Y on a circuit board is cheaper than producing a chip that does X&Y.

Louis_Carole · 10-22-2012, 11:14 AM

I won't knock 'em for making lemonade. That's what I'm trying to do! I declare this solved enough. Thanks again, WW.