On Thu, Mar 20, 2003 at 10:52:57PM +1200, Gareth Williams wrote: > On Thursday 20 March 2003 21:57, Mike Beattie wrote: > > What do you class as a router? A router is in charge of routing packets > > from one network onto another, and vice versa. Therefore, having only 2 > > sockets is quite acceptable. > > I thought the idea of a router was that it had to chose one particular route > (ie. interface?) from a selection, based on rules (routing tables etc)... If > there is only one in, and out, then... where does a routing decision need to > be made? You're just linking 2 networks together.. if a packet hits one > interface that's destined for the other network, you retransmit it on the > other interface, otherwise you don't... it shouldn't even need to 'speak' IP > (unlike a router?) .... sounds like an ethernet bridge to me, no?
If the box has multiple sockets, it would be easy to see that the "router" was able to separate traffic between the local machines, from traffic going out of your network. An ethernet bridge would do that for you, as you say - especially if you taught it the list of MAC addresses on each side of the interface. But what's the MAC address of google? IP provides a way of talking to a machine whose details you don't know - i.e. it mught not even be on an Ethernet (could be X.25, token ring, or anything at the other end. Especially ppp :-). The only thing you know about the remote machine is it's IP address, and the only thing that your PC knows is it's own IP address, and it's current netmask. Every packet that does not belong on the local network has to go somewhere, because the PC does not know how the Internet is structured. So it sends the IP packet to it's local router. It's the router's job to find out how the Internet is structured :-) (in practice, your local router will just send it to the ISP's router. They send the packet to their edge router. The edge router does know how the Internet is structured, because it's running BGP or something like that) So, even with only two interfaces, the router still has to do a fair bit of work ... The old name for routers is "gateway", and most iof the gates you see in the real world only have two sides :-) -jim
