View Source: DestinationNetworkUnreachable

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[ICMP] reason subcode 0, used with ICMP reason code 3 to explain why a DestinationUnreachable message was sent.

If a router cannot forward a packet because it has no routes at all (including no default route) to the destination specified in the packet, then the router must generate a Network Unreachable.

It is usally generated by a gateway when it does not have a route for the destination specified in the IP packet that caused the error.

Note a server with a default gateway won't ever issue this message (since it always has a route for packets...).

Reject routes can also solicit this error.  I recommend you add the routes below to any machine that is physically on the internet.  It'll make any packet that doesn't have a more specific route (via some VPN, or locally connected machine) generate an [ICMP] DestinationNetworkUnreachable message and not just leak random IP's out onto the Internet.
 route add -net 10.0.0.0/8 reject metric 10000
 route add -net 192.168.0.0/16 reject metric 10000

One page links to DestinationNetworkUnreachable:

DestinationNetworkUnknown

Last edited on Thursday, April 12, 2007 3:04:58 pm by BenStaz

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