Configuring IPv6 for Gigabit Ethernet Interfaces
S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
Path MTU Discovery for IPv6
As in IPv4, path MTU discovery in IPv6 allows a host to dynamically discover and adjust to differences
in the MTU size of every link along a given data path. In IPv6, however, fragmentation is handled by the
source of a packet when the path MTU of one link along a given data path is not large enough to
accommodate the size of the packets. Having IPv6 hosts handle packet fragmentation saves IPv6 router
processing resources and helps IPv6 networks run more efficiently.
In IPv4, the minimum link MTU is 68 octets, which means that the MTU size of every link along a given
data path must support an MTU size of at least 68 octets.
In IPv6, the minimum link MTU is 1280 octets. We recommend using an maximum transmission unit
(MTU) value of 1500 octets for IPv6 links.
IPv6 Neighbor Discovery
The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast addresses to
determine the link-layer address of a neighbor on the same network (local link), verify the reachability
of a neighbor, and keep track of neighboring routers.
IPv6 Neighbor Solicitation and Advertisement Messages
A value of 135 in the Type field of the ICMP packet header identifies a neighbor solicitation message.
Neighbor solicitation messages are sent on the local link when a node wants to determine the link-layer
address of another node on the same local link. (See
link-layer address of another node, the source address in a neighbor solicitation message is the IPv6
address of the node sending the neighbor solicitation message. The destination address in the neighbor
solicitation message is the solicited-node multicast address that corresponds to the IPv6 address of the
destination node. The neighbor solicitation message also includes the link-layer address of the source
OL-16184-01, Cisco MDS SAN-OS Release 3.x
46-7.) When a node wants to determine the
Cisco MDS 9000 Family CLI Configuration Guide