bravo good explanation Jim On Thu, 20 Mar 2003 20:25:27 +0000 Jim Cheetham <[EMAIL PROTECTED]> wrote:
> 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 > >
