Default gateway

Hi,

can some one explain what is meant by a default gateway and which node acts like a default gateway normally ?

The default gateway is the path through which packets move if the destination is not within the local network.
You only need a default gateway if you are communicating between two networks.
Therefore the default gateway is the router node on which the LAN is attached to.
For example if a LAN is attached to FastEthernet 0/0
interface of the Router, ALL hosts on that LAN will have a default gateway that is the ip address of the FastEhternet 0/0 interface.

Does you mean to say that router is teh default gateway ?

Then if so why are we referring 2 names here ..

Routers sometimes called default gateway.

Does you mean to say that router is teh default gateway ?

Then if so why are we referring 2 names here ..

In Laymans terms, the router is the gate you use to reach other (remote) networks. Without this gate you woun't have access to any other network apart from yours.

Therefore you configure a default gateway on your network so that packets destined for other (remote) networks go to the router to be directed which gate to use to reach the other network.

'Default gateway' is the precise technical term for the "gateway of last resort" as defined within the specifications of IP itself. In practice as you say the default gateway will probably be a router, but you might have one or more routers on your network being used for other things that aren't acting as default gateways so the terms aren't necessarily interchangeable.
To understand what the default gateway is you need to understand how IP routing works. Basically when a PC on a network wants to send a packet it will look at the destination IP address it needs to send to and at the subnet mask. Using these it will decide whether the destination is on the local IP network (the same one this PC is connected to) or on a distant one that is somewhere else. If it is somewhere else then the packet needs to be sent to a gateway (or router) that can transport it to that remote network. The PC will then look in its routing table to see whether a specific gatway has been defined by which it can reach the network in question. If there is one, the PC will send the packet to that gateway. If there isn't then the PC has to send the packet somewhere so it will send it to it's default gateway - the place all packets go to if they need to be sent to a distant network but we don't have any specific instructions on how to get there