Appendix E IPv6
VMG1312-B Series User’s Guide
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the t im e T2 is reached and the server does not respond, the client sends a Rebind m essage to any
available server (S2 ) . For an I A_TA, t he client m ay send a Renew or Rebind m essage at t he client 's
discret ion.
DHCP Relay Agent
A DHCP r elay agent is on t he sam e network as the DHCP client s and helps forward m essages
bet ween the DHCP server and client s. When a client cannot use it s link-local address and a well-
known m ulticast address to locat e a DHCP server on it s network, it then needs a DHCP relay agent
to send a m essage to a DHCP server t hat is not at t ached to the sam e network.
The DHCP relay agent can add t he rem ot e ident ification (rem ot e-I D) opt ion and the interface-I D
opt ion t o the Relay- Forward DHCPv6 m essages. The rem ot e-I D option carries a user- defined st ring,
such as t he system nam e. The interface-I D opt ion provides slot num ber, port inform at ion and the
VLAN I D to the DHCPv6 server. The r em ot e-I D opt ion (if any) is stripped from t he Relay- Reply
m essages before t he relay agent sends the packets t o the client s. The DHCP server copies t he
interface-I D opt ion from the Relay- Forward m essage into the Relay-Reply m essage and sends it to
the relay agent . The int erface-I D should not change even after t he relay agent restarts.
Prefix Delegation
Prefix delegat ion enables an I Pv6 router to use t he I Pv6 prefix (network address) received from t he
I SP (or a connect ed uplink router) for its LAN. The Device uses the received I Pv6 prefix ( for
exam ple, 2001: db2: : / 48) to generate it s LAN I P address. Through sending Rout er Advertisem ents
( RAs) regularly by m ulticast , t he Device passes the I Pv6 prefix inform at ion t o its LAN hosts. The
host s t hen can use the prefix t o generate their I Pv6 addresses.
ICMPv6
I nternet Control Message Prot ocol for I Pv6 ( I CMPv6 or I CMP for I Pv6) is defined in RFC 4443.
I CMPv6 has a preceding Next Header value of 58, which is different from t he value used to identify
I CMP for I Pv4. I CMPv6 is an int egral part of I Pv6. I Pv6 nodes use I CMPv6 t o report errors
encountered in packet processing and perform other diagnost ic functions, such as "ping".
Neighbor Discovery Protocol (NDP)
The Neighbor Discovery Prot ocol ( NDP) is a prot ocol used t o discover other I Pv6 devices and t rack
neighbor’s reachability in a network. An I Pv6 device uses t he following I CMPv6 m essages types:
• Neighbor solicit at ion: A request from a host t o determ ine a neighbor’s link-layer address ( MAC
address) and det ect if the neighbor is st ill reachable. A neighbor being “ reachable” m eans it
responds t o a neighbor solicitat ion m essage ( from the host ) wit h a neighbor advert isem ent
m essage.
T1
T2
Renew
Rebind
Rebind
to S1
Renew
to S1
Renew
to S1
Renew
to S1
Renew
to S1
Renew
to S1
to S2
to S2
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