Forwarding of traffic with private IP destination addresses

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Sep 30th, 2009
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A co-worker of mine insists that a router, by default, will not forward traffic that is destined for a private IP address unless that private IP is specifically configured, either via a routing protocol or static routing. He thinks that if you only have a default route configured and try to send to a private IP address, the router will drop it, because it's considered "non-routeable".

For example, say you had no static routes and no routing protocol configured, only a static default route ( and a single path out, and then tried to send a packet to My co-worker thinks that the router would drop this packet.

I think that the router doesn't enforce those rules, at least not by default. The router doesn't know whether it's on a private LAN or if it's an edge router on the Internet. I think those "non-routeable" rules have to be configured, otherwise the router will attempt to match the packet against it's routing/forwarding table, and if it doesn't find a match, will just forward it out according to its default route.

So who's right - me or my co-worker? Please say me...ha ha.

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paolo bevilacqua Wed, 09/30/2009 - 06:07
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You are right.

Router doesn't enforce anything and unless destination address is all 0s or multicast, will forward it with a default route.


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