Default Route working

Unanswered Question
May 28th, 2008

How default route works as configuring a gateway for a subnet works and understandable but by adding a gateway for different subnets through default route it start to understand all the subnets.So my question is that default route packet adds some sort of flag in its packet for the gateway that he starts forwarding everything.

I have this problem too.
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ralphcarter Wed, 05/28/2008 - 04:31

The default route "ip route 0.0.0.0 0.0.0.0 x.x.x.x" is placed in the routing table to tell your router where to route packets for destinations not defined in the routing table.

So you can have a default gateway for one of your subnets pointing to the router, but when the router receives the packet, it needs to know how to forward this packet. The default route is used when the routing table has no specific route for the destinaton of a packet.

bvsnarayana03 Wed, 05/28/2008 - 04:48

The function of default-route is different in case of a classless routig on router & when clasless routing is not enabled on router.

Classless routing-When a default route exists, and no specific match is made when comparing

the destination of the packet and the routing table, the default route is used.

Classful routing-When a default route exists, and the class A, B, or C network for the destination IP address does not exist at all in the routing table, the default route is used. If any part of that classful network exists in the routing table, but the packet does not match any of the existing subnets of that classful network, the router does not use the default route and

thus discards the packet.

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