Because a host at system startup typically does not have a unicast IPv6 address, the source address in the router solicitation message is
usually the unspecied IPv6 address (0:0:0:0:0:0:0:0). If the host has a unicast IPv6 address, the source address is the unicast IPv6
address of the host interface sending the router solicitation message.
Entering the ipv6 unicast-routing command automatically enables the sending of router advertisement messages on all congured
router Ethernet interfaces. You can congure several router advertisement message parameters. For information about disabling the
sending of router advertisement messages and the router advertisement parameters that you can congure, refer to Enabling and
disabling IPv6 router advertisements on page 174 and Setting IPv6 router advertisement parameters on page 172.
Neighbor redirect messages
After forwarding a packet, by default, a router can send a neighbor redirect message to a host to inform it of a better
rst-hop router. The
host receiving the neighbor redirect message will then readdress the packet to the better router.
A router sends a neighbor redirect message only for unicast packets, only to the originating node, and to be processed by the node.
A neighbor redirect message has a value of 137 in the Type eld of the ICMP packet header.
Setting neighbor solicitation parameters for duplicate address detection
Although the stateless auto conguration feature assigns the 64-bit interface ID portion of an IPv6 address using the MAC address of
the host’s NIC, duplicate MAC addresses can occur. Therefore, the duplicate address detection feature veries that a unicast IPv6
address is unique before it is assigned to a host interface by the stateless auto conguration feature. Duplicate address detection veries
that a unicast IPv6 address is unique.
If duplicate address detection identies a duplicate unicast IPv6 address, the address is not used. If the duplicate address is the link-local
address of the host interface, the interface stops processing IPv6 packets.
NOTE
Duplicate Address Detection (DAD) is not currently supported with IPv6 tunnels. Make sure tunnel endpoints do not have
duplicate IP addresses.
You can congure the following neighbor solicitation message parameters that aect duplicate address detection while it veries that a
tentative unicast IPv6 address is unique:
• The number of consecutive neighbor solicitation messages that duplicate address detection sends on an interface. By default,
duplicate address detection sends three neighbor solicitation messages without any follow-up messages.
• The interval in seconds at which duplicate address detection sends a neighbor solicitation message on an interface. By default,
duplicate address detection sends a neighbor solicitation message every 1000 milliseconds.
For example, to change the number of neighbor solicitation messages sent on Ethernet interface 1/3/1 to two and the interval between
the transmission of the two messages to 9 seconds, enter the following commands.
device(config)#interface ethernet 1/3/1
device(config-if-e1000-1/3/1)#ipv6 nd dad attempt 2
device(config-if-e1000-1/3/1)#ipv6 nd ns-interval 9000
Syntax: [no] ipv6 nd dad attempt number
Syntax: [no] ipv6 nd ns-interval number
For the number of neighbor solicitation messages, specify a number from 0 - 255. The default is 3. Conguring a value of 0 disables
duplicate address detection processing on the specied interface. To restore the number of messages to the default value, use the no
form of this command.
IPv6 neighbor discovery conguration
FastIron Ethernet Switch Layer 3 Routing
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