Cisco 500 Series, Configuration Manual

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Cisco Security Appliance Command Line Configuration Guide
OL-12172-03
Chapter 12 Configuring IPv6
Configuring IPv6
Valid values for the value argument range from 0 to 3600000 milliseconds. The default is 0.
This information is also sent in router advertisement messages.
When 0 is used for the value , the reachable time is sent as undetermined. It is up to the receiving devices
to set and track the reachable time value. To see the time used by the security appliance when this value
is set to 0, use the
show ipv6 interface command to display information about the IPv6 interface,
including the ND reachable time being used.
Configuring Router Advertisement Messages
Router advertisement messages (ICMPv6 Type 134) are periodically sent out each IPv6 configured
interface of the security appliance. The router advertisement messages are sent to the all-nodes multicast
address.
Figure 12-2 IPv6 Neighbor Discovery—Router Advertisement Message
Router advertisement messages typically include the following information:
•
One or more IPv6 prefix that nodes on the local link can use to automatically configure their IPv6
addresses.
•
Lifetime information for each prefix included in the advertisement.
•
Sets of flags that indicate the type of autoconfiguration (stateless or stateful) that can be completed.
•
Default router information (whether the router sending the advertisement should be used as a default
router and, if so, the amount of time (in seconds) the router should be used as a default router).
• Additional information for hosts, such as the hop limit and MTU a host should use in packets that it
originates.
•
The amount of time between neighbor solicitation message retransmissions on a given link.
•
The amount of time a node considers a neighbor reachable.
Router advertisements are also sent in response to router solicitation messages (ICMPv6 Type 133).
Router solicitation messages are sent by hosts at system startup so that the host can immediately
autoconfigure without needing to wait for the next scheduled router advertisement message. Because
router solicitation messages are usually sent by hosts at system startup, and the host does not have a
configured unicast address, the source address in router solicitation messages is usually the unspecified
IPv6 address (0:0:0:0:0:0:0:0). If the host has a configured unicast address, the unicast address of the
interface sending the router solicitation message is used as the source address in the message. The
destination address in router solicitation messages is the all-routers multicast address with a scope of the
link. When a router advertisement is sent in response to a router solicitation, the destination address in
the router advertisement message is the unicast address of the source of the router solicitation message.
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Router advertisement packet definitions:
ICMPv6 Type = 134
Src = router link-local address
Dst = all-nodes multicast address
Data = options, prefix, lifetime, autoconfig flag
Router
advertisement Router
advertisement