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Routers and MAC Addresses / ARP

Discussion in 'Networks' started by Twonk, Jan 19, 2009.

  1. Twonk

    Twonk New Member

    Hi All,

    Got a question about Routers and how they use ARP / Mac Addresses

    Now I know that a router will use ARP to send data link frames onto a specific host if it's on it's network and use it's ARP table to look it up (or do an ARP broadcast if it doesn't know it)

    What I'd like to know is how does the process work when it's router to router, i.e traversing the Internet over multiple hops to get where it needs to be.

    Im guessing it can't work purely on MAC Addresses because then there would be no need for layer3 (IP) addressing whatsoever. Does a router forward onto the next logical hop (another router) by IP only? If it does this, I don't understand how the data would ever physically reach the network card.

    Hope someone understands what I'm trying to ask!!!
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

    First - ARP and MAC addresses are used on Ethernet segments only. So between your router and your ISP, which isn't Ethernet, they aren't used.

    Second - routers use routing tables - either static preloaded ones, or dynamically updated ones.

    The router in your home will have a routing table to tell it to send anything that isn't on the local Ethernet to the ISP link (dial or ADSL).

    With most routers there should be a page that shows the routing table somewhere in its config pages.

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