bridge detection

["G.P.M" <ice4ice () excite com>]

hi,
   I was wondering are there any programs which can detect switches/routers, based as well on linux.
   The problem is that one company is setting up large LAN, with internet access, based on static ip/mac address, for 
paying reasons. Many clients seperate their connection, often giving mac of the bridge not the PC.
   i had many ideas about that, eg. checking the vendor for the mac, signal replays from the source.
i worry also about 'clear' switches, non programmable ones.

  Could please someone give me some advise?

sorry for my bad english.

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