From: simon hart (simon.hart@btinternet.com)
Date: Sat Feb 12 2005 - 13:19:24 GMT-3
Hi see if can help.
As far as I know this is normally used on Multicast Media and is a means by
which an interface (or NIC) can determine both its local and globally scoped
IPv6 address.
First the Interface will generate a Link Local address by prefixing its own
MAC address to the well known link local prefix FE80::/10. The Interface
will then send out a Router Solicitation message (although it could just
wait for a Router Advertisement message).
Next the interface will send a Neighbor solicitation message - this is to
make sure that no one else is using the link-local prefix. If the address
is in use by another interface then this interface will recieve a Neighbor
advertisement message. If this is the case, then IPv6 stateless
autoconfiguration will terminate. The IP address will have to applied in
another manner (ie DHCPv6 or Manual configuration).
The Interface will now listen for Router Advertisement messages (these
messages are multicast periodically on the link - the message is contained
within an ICMPv6 packet). The Interface can, from these messages, determine
its Globally Scoped address (IPv6 aggregatable unicast address) eg:
2001:0408:001F::/64. Armed with this information the interface can now
apply this prefix and thus talk locally and to the rest of the world in IPv6
speak.
I believe that Cisco Routers will automatically pick up the Link Local
address by default (that is FE80::/10 + MAC address). Therefore the command
IPv6 address autoconfig will allow the router to pick up a Globally
significant address. This saves having to type out long hex numbers on each
interface, or having to use DHCP.
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
ccie2be
Sent: 12 February 2005 15:35
To: Group Study
Subject: ipv6 address autoconfig
Hi guys,
What pre-requisites, if any, exist for using this command?
I can see from the command reference below what this command does but I
don't understand when I can or should use this command. If someone can
provide a simple example or scenario that illustrates how this command
should or shouldn't be used, I would be very grateful.
Thanks, Tim
ipv6 address autoconfig
To enable automatic configuration of IPv6 addresses using stateless
autoconfiguration on an interface and enable IPv6 processing on the
interface, use the ipv6 address autoconfig command in interface
configuration mode. Addresses are configured depending on the prefixes
received in Router Advertisement messages. To remove the address from the
interface, use the no form of this command.
ipv6 address autoconfig
no ipv6 address autoconfig
Syntax Description
This command has no keywords or arguments.
Defaults
No IPv6 address is defined for the interface.
Command Modes
Interface configuration
Command History
Release Modification
12.2(13)T This command was introduced.
Usage Guidelines
If the Cisco IOS software detects another host using one of its IPv6
addresses, it will display an error message on the console.
The system automatically generates a link-local address for an interface
when IPv6 processing is enabled on the interface, typically when an IPv6
address is configured on the interface.
If router advertisements (RAs) received on this interface have the "other
configuration" flag set, then the interface will also attempt to acquire
other configuration (i.e., non-address) using DHCP for IPv6.
Examples
The following example assigns the IPv6 address automatically.
Router(config)# interface ethernet 0
Router(config-if)# ipv6 address autoconfig
This archive was generated by hypermail 2.1.4 : Thu Mar 03 2005 - 08:51:20 GMT-3