I have PC->Router->DSL Modem->ISP, Does ISP Router learn the PC MAC address?

Router's are layer 3 devices. Layer 3 of the OSI layers that is. Layer

3 devices in normal operation overwrite the layer 2 information of a packet (the mac address). So only your router knows your mac address. Your ISP knows the mac address of your Router and associates that mac address with the IP address of your router (the IP address that your ISP gave you). Other routers out on the internet past your directly connected segment may only know the IP address of your router. They have a route table saying that in order to get there, they must send to the next router in the path, and they know the mac address of only the next hop, not the mac address of the final destination. This is how the typical ethernet segments are pieced together. ISP's of course use many different methods for moving data around on the internet, ethernet being rare and SONET, ATM and others being more prevelant. If you wish to write a network application, I suggest you lookup and study the OSI model, and take a look here at the already assigned TCP/UDP ports: Kevin

Kevin,

I ma little confused here, so my home Router knows only my PC's MAC address and IP, similarly My Routers's IP and MAC is known by my ISP (I have Cable modem in the middle, that doesn't have any MAC or IP?). In that case my ISP used IP + MAC to send and receive packets from corresponding web address right?. I am trying to understand why IP and MAC required, why not only one?. Why this MAC address came into picture since every PC/Router had IP address?. Thanks.

In article , wrote: :I ma little confused here, so my home Router knows only my PC's MAC :address and IP, similarly My Routers's IP and MAC is known by my ISP (I :have Cable modem in the middle, that doesn't have any MAC or IP?). In :that case my ISP used IP + MAC to send and receive packets from :corresponding web address right?. I am trying to understand why IP and :MAC required, why not only one?. Why this MAC address came into picture :since every PC/Router had IP address?. Thanks.

Not every ethernet device has an IP address. IP is -one- of the possible mid-layer communications protocols. Appletalk and IPX (Novell) are two other well-known mid-layer communications protocols.

Within a LAN, all the -real- work of deliverying packets is handled by MAC address. Outside of a LAN, all the real work of getting packets over multiple hops is done by IP address, with the MAC address being continually changed along the way in order to do device-to-device conversations.

Roughly speaking, your ISP gets your packets as far as your router by using the IP address. Once the packet is at your router, the router sends out a broadcast message saying, "I have a package here for Mr. Frank N. Packet", and your PC responds with, "That's me, I'm at pnuematic tube #182!"; your router then remembers that information for awhile, and further packets to Frank N. Packet are dropped into pneumatic tube #182 without pausing to check to see whether Frank N. Packet is still there or is Out To Lunch.

Or if you prefer, think of it as addressing a letter to a particular job title at a corporate office. The corporate address is what the mail system uses to get the letter as far as the corporate mailroom, and the mailroom looks up the appropriate office number; once that is done, delivery is done to the office. The same person might have several different roles, and receive mail for "Job Applications", "Head, Finances", and "Accounts Receivable" -- the mailroom can handle that easily, without requiring that each different role's mail be delivered to a different office.

Walter, Thanks for nice explanation, appreciated.