ZyXEL Communications VMG1312-B Series User Manual page 354

Appendix E IPv6
t he t im e T2 is reached and t he server does not respond, t he client sends a Rebind m essage t o 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 relay agent is on t he sam e net work as t he DHCP client s and helps forward m essages
bet ween t he DHCP server and client s. When a client cannot use it s link- local address and a well-
known m ult icast address t o locat e a DHCP server on it s net work, it t hen needs a DHCP relay agent
t o send a m essage t o a DHCP server t hat is not at t ached t o t he sam e net work.
The DHCP relay agent can add t he rem ot e ident ificat ion ( rem ot e- I D) opt ion and t he int erface- I D
opt ion t o t he Relay- Forward DHCPv6 m essages. The rem ot e- I D opt ion carries a user- defined st ring,
such as t he syst em nam e. The int erface- I D opt ion provides slot num ber, port inform at ion and t he
VLAN I D t o t he DHCPv6 server. The rem ot e- I D opt ion ( if any) is st ripped from t he Relay- Reply
m essages before t he relay agent sends t he packet s t o t he client s. The DHCP server copies t he
int erface- I D opt ion from t he Relay- Forward m essage int o t he Relay- Reply m essage and sends it t o
t he relay agent . The int erface- I D should not change even aft er t he relay agent rest art s.
Prefix Delegation
Prefix delegat ion enables an I Pv6 rout er t o use t he I Pv6 prefix ( net work address) received from t he
I SP ( or a connect ed uplink rout er) for it s LAN. The Device uses t he received I Pv6 prefix ( for
exam ple, 2001: db2: : / 48) t o generat e it s LAN I P address. Through sending Rout er Advert isem ent s
( RAs) regularly by m ult icast , t he Device passes t he I Pv6 prefix inform at ion t o it s LAN host s. The
host s t hen can use t he prefix t o generat e t heir I Pv6 addresses.
ICMPv6
I nt ernet Cont rol 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 t o ident ify
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
encount ered in packet processing and perform ot her diagnost ic funct ions, such as " ping" .
Neighbor Discovery Protocol (NDP)
The Neighbor Discovery Prot ocol ( NDP) is a prot ocol used t o discover ot her I Pv6 devices and t rack
neighbor 's reachabilit y in a net work. An I Pv6 device uses t he following I CMPv6 m essages t ypes:
• Neighbor solicit at ion: A request from a host t o det erm ine a neighbor 's link- layer address ( MAC
address) and det ect if t he neighbor is st ill reachable. A neighbor being " reachable" m eans it
responds t o a neighbor solicit at ion m essage ( from t he host ) wit h a neighbor advert isem ent
m essage.
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T1
Renew
to S1
Renew
to S1
T2
Renew
Renew
to S1
to S1
Renew
Renew
to S1
to S1
Rebind
to S2
Rebind
to S2
VMG1312-B Series User's Guide