Field Name

Size (bytes)

Description

Type

1

Type: Identifies the ICMPv6 message type; for Redirect messages the value is 137.

Code

1

Code: Not used; set to 0.

Checksum

2

Checksum: 16-bit checksum field for the ICMP header, as described in the topic on the ICMP common message format.

Reserved

4

Reserved: 4 bytes sent as zeroes.

Target Address

16

Target Address: The address of the router that the router creating the Redirect is telling the recipient of the Redirect to use as a first hop for future transmissions to the destination. Phew. Example time: if router R2 generated a Redirect telling host A that in the future transmissions to host B should be sent first to router R1, then R1's IPv6 address would be in this field.

Destination Address

16

Destination Address: The address of the device whose future transmissions are being redirected; this is the destination of the datagram that originally led to the Redirect being generated. Repeating the example above: if router R2 generated a Redirect telling host A that in the future transmissions to host B should be sent first to router R1, then host B's IPv6 address would be in this field.

Options

Variable

Options: Redirect messages normally include two ICMPv6 option fields:

[ Target Link-Layer Address: The layer-two address of the Target Address, if known. This saves the recipient of the Redirect message from needing to perform an address resolution on the target.

[ Redirected Header: As much of the IPv6 datagram that spawned this Redirect as will fit without causing the size of the ICMPv6 error message (including its own IP header) to exceed the minimum IPv6 maximum transmission unit (MTU) of 1280 bytes.