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Old 12-17-2003, 02:28 AM   #1
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Please restate in a more technical manner - home LAN

I am a newbie, and just successfully set up my first home LAN; it's aLAN (let's call it small LAN) within a LAN (let's call it big LAN), the big LAN being our home lan set up by my able brother.

I set my router to do dynamic IP.

The two routers (small and big LANs') have the same default and I kinda figured out (please correct me if I'm wrong) that the reason I cannot access the internet from the small LAN is because the traffic sort of *loops* within itself, since its default gateway is which is essentially itself. It cannot forward any request to the next router.

I changed the small LAN's IP to .... the pc's eventually were assigned its own 192.168.168.* address - and, voila, the PCs can access the net now.

Now ... if anyone can kindly restate that in a more technical - maybe more correct - manner, I'd really appreciate it !!!!!!!!!!

Thanks !

Old 12-17-2003, 04:41 AM   #2
Registered: Dec 2003
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Distribution: Redhat WS 3
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Consider now two separate Ethernet networks that are joined by a PC, C, acting as an IP router (for instance, if you have two Ethernet segments on your server).

Device C is acting as a router between these two networks. A router is a device that chooses different paths for the network packets, based on the addressing of the IP frame it is handling. Different routes connect to different networks. The router will have more than one address as each route is part of a different network.

Since there are two separate Ethernet segments, each network has its own Class C network number. This is necessary because the router must know which network interface to use to reach a specific node, and each interface is assigned a network number. If A wants to send a packet to E, it must first send it to C who can then forward the packet to E. This is accomplished by having A use C's Ethernet address, but E's IP address. C will receive a packet destined to E and will then forward it using E's Ethernet address. These Ethernet addresses are obtained using ARP as described earlier.

If E was assigned the same network number as A, 200.1.2, A would then try to reach E in the same way it reached C in the previous example - by sending an ARP request and hoping for a reply. However, because E is on a different physical wire, it will never see the ARP request and so the packet cannot be delivered. By specifying that E is on a different network, the IP module in A will know that E cannot be reached without having it forwarded by some node on the same network as A.


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