The TCP/IP Guide - ICMPv6 Neighbor Advertisement and Neighbor Solicitation Messages

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The Neighbor Solicitation message format is much simpler, as depicted in Table 112 and Figure 161.

**Table 112: ICMPv6 *Neighbor Solicitation* Message Format**
Field Name	Size (bytes)	Description
*Type*	1	*Type:* Identifies the ICMPv6 message type; for Neighbor Solicitation messages the value is 135.
*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 reserved bytes set to 0.
*Target Address*	16	*Target Address:* The IPv6 address of the target of the solicitation. For IPv6 address resolution, this is the actual unicast IP address of the device whose layer two (link-layer) address we are trying to resolve.
*Options*	Variable	*Options:* If the device sending the Neighbor Solicitation knows both its own IP address and layer two address, it should include the layer two address in a Source Link-Layer Address option. The inclusion of this option will allow the destination of the Neighbor Solicitation to enter the layer two and layer three addresses of the source of this message into its own address cache. See the discussion of IPv6 address resolution.