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Wikipedia lists 4 types of ICMP Redirect reasons:

0   Redirect for Network
1   Redirect for Host
2   Redirect for Type of Service and Network
3   Redirect for Type of Service and Host

I understand the purpose of ICMP Redirect, but why is there a need to distinguish between, say, a Network and a Host?

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Granularity, the possibility that single hosts might have different policies than others, or the network as a whole? – NickW May 13 '13 at 15:59
up vote 1 down vote accepted

In RFC 1812, there is a section about ICMP redirect that make your problem becomes clearly. Like this:

If the directly connected network is not subnetted (in the classical sense), a router can normally generate a network Redirect that applies to all hosts on a specified remote network. Using a network rather than a host Redirect may economize slightly on network traffic and on host routing table storage. However, the savings are not significant, and subnets create an ambiguity about the subnet mask to be used to interpret a network Redirect. In a CIDR environment, it is difficult to specify precisely the cases in which network Redirects can be used. Therefore, routers must send only host (or host and type of service) Redirects.

Best regards.

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