3.1.b Identify, implement and troubleshoot IPv6 addressing and subnetting

3.1.b [iii] ND, RS/RA

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 track neighboring devices.

The IPv6 static cache entry for neighbor discovery feature allows static entries to be made in the IPv6 neighbor cache. Static routing requires an administrator to manually enter IPv6 addresses, subnet masks, gateways, and corresponding MAC addresses for each interface of each device into a table. Static routing enables more control but requires more work to maintain the table.The table must be updated each time routes are added or changed.

By definition, a router is a node that forwards IP packets not explicitly addressed to it. IPv6 routers are compliant with this definition but , in addition, they regularly advertise information on the links to which they are connected— provided they are configured to do so. These advertisements are ICMPv6 Router Advertisement (RA) messages, sent to the multicast group FF02:: 1. All the systems on a link must belong to this group, and nodes configured for auto-configuration, among other things, analyze the option( s) of those messages. They might contain any routing prefix( es) for this segment.

Router Solicitation

Upon reception of one of those RA messages and according to local algorithm policy, an auto-configuring node not already configured with the corresponding global address will prepend the advertised prefix to the unique identifier built previously. However, the advertisement frequency, which is usually about ten seconds or more, may seem too long for the end user. In order to reduce this potential wait time, nodes can send Router Solicitation (RS) messages to all the routers on the link. Nodes that have not configured an address yet use the unspecified address “::”. In response, the routers must answer immediately with a RA message containing a global prefix. This router solicitation corresponds to ICMPv6 messages of type RS, sent to the all-router multicast group FF02:: 2. All routers on the link must join this group.

Thus, a node soliciting on-link routers in such a way is able to extract a prefix and build its global address. The method of using an advertised prefix is possible only for end nodes. IPv6 routers are usually manually configured as a stateless automatic configuration requires the advertisement of a prefix. This prefix is sent by a router. The router sending the prefix must be fully configured to do so.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2308-2315).  . Kindle Edition.