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Understanding the Protocol Redirect Mechanism on EX Series Switches
Internet Control Message Protocol (ICMP) redirect, also known as protocol redirect, is a mechanism used by switches and routers to convey routing information to hosts. ICMP redirect messages are used by switches and routers to notify the hosts on the same data link of the best route available for a given destination. All EX series switches support sending ICMP redirect messages for both IPv4 and IPv6 traffic.
 | Note: EX series switches do not send ICMP redirect messages if the data packet contains routing information. |
The ICMP redirect messages inform a host to update its routing information and to send packets on an alternate route. Suppose a host tries to send a data packet through a switch (say, S1) and S1 sends the data packet to another switch (say, S2). Also, suppose that a direct path from the host to S2 is available (that is, the host and S2 are on the same Ethernet segment). S1 then sends a protocol redirect message to inform the host that the best route for the destination is the direct route to S2. The host should then send packets directly to S2 instead of sending them through S1. S2 still sends the original packet that it received from S1 to the intended destination. Refer to RFC-1122 and RFC-4861 for more details on ICMP redirecting.
By default, the switch sends protocol redirect messages. For security reasons, you might want to disable the switch from sending protocol redirect messages.
