Any Router experts ? - as in how they work

Would like an explanation of how they manage to route correctly ?

scenario

router + 2 pcs

if both dial say news.bbc.co.uk , does the router have some sort of table

with a list of ips asked for by each connected pc ?

intrigued to how it routes if the same web site asked for

thanks

Run a trace; in WinXp get a DOS command{Start/Run} and type in "CMD",
all without quotes.
type "tracert www.bbc.co.uk"
<Note space after tracert>
and see route and time taken to reach destination.

"zero" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Would like an explanation of how they manage to route correctly ?
>
> scenario
>
> router + 2 pcs
>
> if both dial say news.bbc.co.uk , does the router have some sort of table
>
> with a list of ips asked for by each connected pc ?
>
> intrigued to how it routes if the same web site asked for

You need to look up how NAT (Network Address Translation) and PAT (Port
Address Translation) works. Your router will overlap requests to the same
external IP which is why multiple requests can go out at the same time.

Here's a good link: http://www.cisco.com/warp/public/556/nat-cisco.shtml

Basically, your router maintains a table of all active connections. It
stores the request to go to the web site so when the return packet comes
back in it knows where to send it on your LAN.

"zero" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Would like an explanation of how they manage to route correctly ?
> scenario router + 2 pcs if both dial say news.bbc.co.uk , does the router
> have some sort of table
> with a list of ips asked for by each connected pc ?
> intrigued to how it routes if the same web site asked for

This scenario works in one of two ways:-

1) Each of the PCs in questions has its own global IP so this is fairly
straight forward as the requested website will see two different requests
from two different global IP addresses which not a problem.

2) There is only one global IP address and the router in question is
performing NAT. In this case each request to the bbc website will come from
a single IP address, but the "reply" is to be sent to a different port. The
router will "simply" relay the IP packets from each port to the appropriate
PC (using a internal routing table which it will maintain).

This is atleast how I understand it to work.

"Clueless2" <no.spam> wrote in news:41d833e2$0$16573$cc9e4d1f@news-
text.dial.pipex.com:

> In this case each request to the bbc website will come from
> a single IP address, but the "reply" is to be sent to a different port.

Not exactly true.

For web browsing it would go as follows:

PC1 TCP SYN from port 50000 -> www.bbc.co.uk port 80
IE 192.168.0.1:50000->212.58.224.116:80

The router would then store a copy of the two sockets in its NAT tables
as a single connection allowing further packets to be relayed back
through that connection.
If the server were to send a reply on a different port, it would get
dropped. If the router receives a RST or FIN packet on a session matching
those ports then it will not pass any further packets (except the RST,ACK
or FIN,ACK) for that session.

Another example is FTP, for direct connections with legitimate IP
addresses, you can use non passive FTP that will go exactly as above for
the control comms. FTP actually uses a second socket for transferring
data.
NAT with no forwarding rules will break non passive FTP as the server
opens the second socket. Passive mode gets around this by the server and
client negotiating the second socket and then the client opening that
socket so that a NAT table will accept the data.

You can probably find more info in whatis.com

zero wrote:
> Would like an explanation of how they manage to route correctly ?
>
> scenario
>
> router + 2 pcs
>
> if both dial say news.bbc.co.uk , does the router have some sort of table
>
> with a list of ips asked for by each connected pc ?
>
> intrigued to how it routes if the same web site asked for
>
> thanks
>
>
>

Have a look at this site http://www.warriorsofthe.net/ the movie
download is fairly large - you'll need broadband.

Most of your questions will be answered in an entertaining and
informative way.

--

Mark²³°°

thanks everyone

looks like a big table is the answer in simple terms

will check the links - at work tomorrow !



"Mark²³°°" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> zero wrote:
> > Would like an explanation of how they manage to route correctly ?
> >
> > scenario
> >
> > router + 2 pcs
> >
> > if both dial say news.bbc.co.uk , does the router have some sort of
table
> >
> > with a list of ips asked for by each connected pc ?
> >
> > intrigued to how it routes if the same web site asked for
> >
> > thanks
> >
> >
> >
>
> Have a look at this site http://www.warriorsofthe.net/ the movie
> download is fairly large - you'll need broadband.
>
> Most of your questions will be answered in an entertaining and
> informative way.
>
> --
>
> Mark²³°°