Routing Question [Newbie]

[RBH]

I have a little routing project coming up and am a little confused in terms of how computers on one subnet "find" a computer on another. I realise that routing tables are how an individual box knows where to go (i.e. which router is their first port of call) for a particular subnet, but how does that box learn of those routes in the first place? Is it something handled by DHCP or is there some other protocol responsible for publishing routes out to clients?

This feels like a really daft question to ask but I'm probably searching for the wrong things.

Any help much appreciated.

[malern]

If you're talking about a standard desktop computer with one NIC, then yes, it's most likely that the default route was obtained via DHCP. Or it was manually specified when the machine was setup.

If you're wondering how things like ISP level routers figure out how to route traffic then they tend to use BGP.

[Veldrin]

Google, or Wikipedia in that case, is your friend...

Basically there are 3 Ways of learning those routes:

• static: the good old manual way
  
• interior routing protocols: RIP, OSPF, EIGRP
  
• exterior routing protocols: BGP, IS-IS

The static way, means to configure every single route, on every single router. As you may imagine, this is a rather time-consuming task.

The developed alternative are routing protocols, which propagate this routing information from one router to another. Those are split into 2 categories: interior routing protocols, and exterior routing protocols. The main difference is the area they are deployed in: interior routing protocols within a (corporate) network, and exterior to route between large networks (think ISP).

Interior routing protocols are metric based (each route has a specified cost), while exterior (only knowing BGP) are policy based (the operator decides where to route to).

cheers
V.

I hope this gives you some insight...