ndp.7p (2010 09)
n
ndp(7P) ndp(7P)
NAME
ndp - Neighbor Discovery Protocol, NDP
DESCRIPTION
Neighbor Discovery Protocol (NDP) is a protocol used by hosts and routers to:
1. Find the link-layer address of the neighbors known to be attached to the same link.
2. Find the neighboring routers that are willing to forward packets on their behalf.
3. Actively keep track of which neighbors are reachable and which are not.
4. Search for alternate routers when the path to a router fails.
To accomplish the above mentioned tasks, NDP defines the following processes:
1. Router and Prefix Discovery
Router discovery is a process through which hosts locate the neighboring routers and learn prefix
plus other parameters necessary for address autoconfiguration.
Prefix discovery is used by the hosts to learn the range of IPv6 addresses that reside on-link and can
be reached without going through a router.
Routers send Router Advertisements which will make the hosts treat them as the default routers.
The Router Advertisements will also contain prefix information options that will identify the range
of IPv6 addresses that are on-link (Subnet prefix).
2. Router and Host Requirements
Router requirements in NDP specify a set of rules for host to act as a router. These rules include:
• Router configuration variables.
These configuration variables include intervals between successive unsolicited router adver-
tisements, etc.
• How to make an interface an advertising interface.
When an interface is made an advertising interface, it means that the node is going to send
periodic router advertisements and is willing to forward packets on behalf of hosts on that
link.
• Message content for router advertisements.
A router will send periodic as well as solicited Router Advertisements on an advertising inter-
face. NDP specifies the format of these messages.
• Sending unsolicited router advertisements.
Apart from sending solicited router advertisements in response to router solicitations, routers
can send unsolicited router advertisements. For example, unsolicited router advertisements
can be sent to expire a prefix or to advertise a new prefix, etc.
• Stopping router advertisements on an interface.
A router can stop advertising prefixes on an interface. This can happen due to system
management decisions when a router may be stopped from being one. NDP specifies what the
router should be doing under these circumstances.
• Processing router solicitation messages.
Hosts as part of the stateless autoconfiguration process will send Router Solicitations. Routers
should respond to such solicitations with a router advertisement.
• Steps to be taken when the link-local address for the router changes.
Normally the link-local address of a Router should not change. However, NDP still defines the
steps should be taken by the router when its link-local address changes for any of its inter-
faces.
Host requirements are a set of rules that apply for a IPv6 host. They are:
• IPv6 variables that have to be maintained.
These variables include the time between retransmissions of neighbor solicitations, link MTU
for each interface, etc.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1