Cisco Systems A9014CFD manual Stateless Autoconfiguration, ICMPv6, 32-5

Chapter 32 IPv6 Support on the Cisco ASR 901 Router

Information About IPv6 Support on the Cisco ASR 901 Router

provides more control over the network but it requires more work to maintain the table. The table must be updated every time routes are added or changed. Moreover, the static routes must be manually reconfigured if there is a change in the network topology.

Static configuration provides security and resource efficiency. It uses less bandwidth than dynamic routing protocols and no CPU cycles are used to calculate and communicate routes. Static routes created by the static configuration can be redistributed into dynamic routing protocols. However, routes generated by dynamic routing protocols cannot be redistributed into the static routing table.

Static configuration is useful for smaller networks with only one path to an outside network and in providing security for a larger network for certain types of traffic or links to other networks that need more control. In general, most networks use dynamic routing protocols to communicate between networking devices but may have one or two static routes configured for special cases.

Stateless Autoconfiguration

All interfaces on IPv6 nodes must have a link-local address, which is usually automatically configured from the identifier for an interface and the link-local prefix FE80::/10. A link-local address enables a node to communicate with other nodes on the link and can be used to further configure the node.

Nodes can connect to a network and automatically generate global IPv6 addresses without the need for manual configuration or help of a Dynamic Host Configuration Protocol (DHCP) server.

With IPv6, a router on the link advertises in RA messages any global prefixes, and its willingness to function as a default router for the link. RA messages are sent periodically and in response to router solicitation messages, which are sent by hosts at system startup.

A node on the link can automatically configure global IPv6 addresses by appending its interface identifier (64 bits) to the prefixes (64 bits) included in the RA messages. The resulting 128-bit IPv6 addresses configured by the node are then subjected to duplicate address detection (DAD) to ensure their uniqueness on the link. If the prefixes advertised in the RA messages are globally unique, then the IPv6 addresses configured by the node are also globally unique. Router solicitation messages, which have a value of 133 in the Type field of the ICMP packet header, are sent by hosts at system startup so that the host can immediately autoconfigure without needing to wait for the next scheduled RA message.

For more information on IPv6 Addressing and Discovery, see the Implementing IPv6 Addressing and Basic Connectivity chapter of IPv6 Configuration Guide, at the following location:

http://www.cisco.com/en/US/docs/ios-xml/ios/ipv6/configuration/15-2mt/ip6-addrg-bsc-con.html

ICMPv6

Internet Control Message Protocol (ICMP) in IPv6 functions the same as ICMP in IPv4. ICMP generates error messages such as ICMP destination unreachable messages, and informational messages such as ICMP echo request and reply messages. Additionally, ICMP packets in IPv6 are used in the IPv6 neighbor discovery process, path MTU discovery, and the Multicast Listener Discovery (MLD) protocol for IPv6.

For more information on ICMPv6, see the Implementing IPv6 Addressing and Basic Connectivity chapter of IPv6 Configuration Guide, at the following location:

http://www.cisco.com/en/US/docs/ios-xml/ios/ipv6/configuration/15-2mt/ip6-addrg-bsc-con.html

	Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09		32-5