ZyXEL Communications VMG1312-B Series User Manual page 105

Multicast
I P packet s are t ransm it t ed in eit her one of t wo ways - Unicast ( 1 sender - 1 recipient ) or Broadcast
( 1 sender - everybody on t he net work) . Mult icast delivers I P packet s t o a group of host s on t he
net work - not everybody and not j ust 1.
I nt ernet Group Mult icast Prot ocol ( I GMP) is a net work- layer prot ocol used t o est ablish m em bership
in a Mult icast group - it is not used t o carry user dat a. I GMP version 2 ( RFC 2236) is an
im provem ent over version 1 ( RFC 1112) but I GMP version 1 is st ill in wide use. I f you would like t o
read m ore det ailed inform at ion about int eroperabilit y bet ween I GMP version 2 and version 1, please
see sect ions 4 and 5 of RFC 2236. The class D I P address is used t o ident ify host groups and can be
in t he range 224.0.0.0 t o 239.255.255.255. The address 224.0.0.0 is not assigned t o any group
and is used by I P m ult icast com put ers. The address 224.0.0.1 is used for query m essages and is
assigned t o t he perm anent group of all I P host s ( including gat eways) . All host s m ust j oin t he
224.0.0.1 group in order t o part icipat e in I GMP . The address 224.0.0.2 is assigned t o t he m ult icast
rout ers group.
At st art up, t he Device queries all direct ly connect ed net works t o gat her group m em bership. Aft er
t hat , t he Device periodically updat es t his inform at ion.
DNS Server Address Assignment
Use Dom ain Nam e Syst em ( DNS) t o m ap a dom ain nam e t o it s corresponding I P address and vice
versa, for inst ance, t he I P address of www.zyxel.com is 204.217.0.2. The DNS server is ext rem ely
im port ant because wit hout it , you m ust know t he I P address of a com put er before you can access
it .
The Device can get t he DNS server addresses in t he following ways.
1 The I SP t ells you t he DNS server addresses, usually in t he form of an inform at ion sheet , when you
sign up. I f your I SP gives you DNS server addresses, m anually ent er t hem in t he DNS server fields.
2 I f your I SP dynam ically assigns t he DNS server I P addresses ( along wit h t he Device's WAN I P
address) , set t he DNS server fields t o get t he DNS server address from t he I SP .
IPv6 Addressing
The 128- bit I Pv6 address is writ t en as eight 16- bit hexadecim al blocks separat ed by colons ( : ) . This
is an exam ple I Pv6 address 2001:0db8:1a2b:0015:0000:0000:1a2f:0000.
I Pv6 addresses can be abbreviat ed in t wo ways:
• Leading zeros in a block can be om it t ed. So 2001:0db8:1a2b:0015:0000:0000:1a2f:0000 can
be writ t en as 2001:db8:1a2b:15:0:0:1a2f:0.
• Any num ber of consecut ive blocks of zeros can be replaced by a double colon. A double colon can
only appear once in an I Pv6 address. So 2001:0db8:0000:0000:1a2f:0000:0000:0015 can be
writ t en as 2001:0db8::1a2f:0000:0000:0015, 2001:0db8:0000:0000:1a2f::0015,
2001:db8::1a2f:0:0:15 or 2001:db8:0:0:1a2f::15.
IPv6 Prefix and Prefix Length
Sim ilar t o an I Pv4 subnet m ask, I Pv6 uses an address prefix t o represent t he net work address. An
I Pv6 prefix lengt h specifies how m any m ost significant bit s ( st art from t he left ) in t he address
VMG1312-B Series User's Guide
Chapter 6 Broadband
105