On 15 Jul 00, at 13:44, Bharat Ale wrote:

> Just an elementary question. What does a router do ? Isn't it
> possible to connect a network to the internet without using a
> router ?

  In general, a router is a special case of gateway, a machine that
is a member of two (or more) different networks for the purpose of
"internetworking" -- allowing traffic between hosts on different
networks.
  [There are two basic kinds of gateway:  proxies, which hide the
fact that there is a whole network beyond them (amongst other things,
this makes protocol conversion practical), and routers, which do not.
 In a typical TCP/IP setup, a proxy rewrites header information at
Layer 3 and a router rewrites header information at Layer 2.]
  There are, of course, lots of extra complications that can be added
to the routing piece:  media conversions, security, multiple
networks, dynamic connections....
  On my desk at work, I have a 10Mbps Ethernet-to-Ethernet router
that cost less than $200; I'm awaiting delivery of a multi-port
router from Cisco whose pricetag was about $23K.  Of course, a router
*could* just be a standard computer with multiple NICs and
appropriate software running.

  Connecting a network to the Internet is going to require some sort
of gateway.  Whether that gateway is a router or something else is a
choice to be made.

David G

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