UMN:CLI User Manual
V5808
364
The delegating router acts as a DHCP server, and is responding to the prefix request. It is
configured with a set of prefixes to be used for assignment to customers at the time of
each customer's first connection to the ISP service. The prefix delegation process begins
when the requesting router requests configuration information through DHCPv6. The
DHCP messages from the requesting router (DHCP client) are received by the delegating
router in the aggregation device. When the delegating router receives the request, it
selects an available prefix or prefixes for delegation to the requesting router. The
delegating router then returns the prefix or prefixes to the requesting router. The
requesting router subnets the delegated prefix and assigns the longer prefixes to links in
the subscriber's network. The requesting router subnets a single delegated /48 prefix into
/64 prefixes and assigns one /64 prefix to each of the links in the subscriber network.
The prefix delegation options can be used in conjunction with other DHCP options
carrying other configuration information to the requesting router. The requesting router
provides DHCP service to hosts attached to the internal network. For example, the
requesting router may obtain the addresses of DNS and NTP servers from the ISP
delegating router, and then pass that configuration information on to the subscriber hosts
through a DHCP server in the requesting router.
DHCPv6 Basic Operation
DHCPv6 clients and servers exchange DHCP messages using UDP port. DHCPv6 clients
listen for DHCP messages on UDP port 546. DHCPv6 servers and relay agents listen for
DHCPv6 messages on UDP port 547. The client can obtain server or relay agent’s
address using All-DHCP-Server and All-DHCP-Agent address.
Clients listen for DHCP messages on UDP port 546.
Server and relay agents listen for DHCP messages on UDP
port 547.
Tab. 8.5 DHCPv6 UDP port
There are no broadcast addresses defined for IPv6. Therefore, the use of the limited
broadcast address for some DHCPv4 messages has been replaced with the use of the
site-scoped multicast address (FF05::1:3) and link-scoped multicast address (FF02::1:2)
for DHCPv6.
All_DHCP_Servers
(Site-local scope)
A site-scoped multicast address used by a relay agent or client
to communicate with servers, either because the relay agent
wants to send messages to all servers or because it does not
know the unicast addresses of the servers. All DHCP servers
within a site are members of this multicast group.
All_DHCP_Relay_Agents
_and_Servers
(Link-local scope)
A link-scoped multicast address used by a client to
communicate with neighboring (i.e., on-link) relay agents and
servers. All servers and relay agents are members of this
multicast group.
Tab. 8.6 DHCPv6 Address
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