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ICMP Redirect & Router Discovery

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ICMP Redirect: R1 tells host to take a shortcut

ICMP Redirect (Type 5) is sent by a router when it forwards a packet out the same interface it arrived on — meaning there's a more efficient path the host should use directly.

This optimizes routing on shared LAN segments: instead of always going through R1, the host learns to send certain traffic directly to R2.

Packets in motion — click to inspect:

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