Igmp Snooping; Igmp Snooping And Vlans - ZyXEL Communications GS2210-8 User Manual

Chapter 24 Multicast

IGMP Snooping

A Swit ch can passively snoop on I GMP packet s t ransferred bet ween I P m ult icast rout ers/ swit ches
and I P m ult icast host s t o learn t he I P m ult icast group m em bership. I t checks I GMP packet s passing
t hrough it , picks out t he group regist rat ion inform at ion, and configures m ult icast ing accordingly.
I GMP snooping allows t he Swit ch t o learn m ult icast groups wit hout you having t o m anually
configure t hem .
The Swit ch forwards m ult icast t raffic dest ined for m ult icast groups ( t hat it has learned from I GMP
snooping or t hat you have m anually configured) t o port s t hat are m em bers of t hat group. I GMP
snooping generat es no addit ional net work t raffic, allowing you t o significant ly reduce m ult icast
t raffic passing t hrough your Swit ch.

IGMP Snooping and VLANs

The Swit ch can perform I GMP snooping on up t o 16 VLANs. You can configure t he Swit ch t o
aut om at ically learn m ult icast group m em bership of any VLANs. The Swit ch t hen perform s I GMP
snooping on t he first 16 VLANs t hat send I GMP packet s. This is referred t o as aut o m ode.
Alt ernat ively, you can specify t he VLANs t hat I GMP snooping should be perform ed on. This is
referred t o as fixed m ode. I n fixed m ode t he Swit ch does not learn m ult icast group m em bership of
any VLANs ot her t han t hose explicit ly added as an I GMP snooping VLAN.
MLD Snooping-proxy
MLD snooping- proxy is a ZyXEL- propriet ary feat ure. I Pv6 MLD proxy allows only one upst ream
int erface on a swit ch, while MLD snooping- proxy support s m ore t han one upst ream port on a
swit ch. The upst ream port in MLD snooping- proxy can report group changes t o a connect ed
m ult icast rout er and forward MLD m essages t o ot her upst ream port s. This helps especially when
you want t o have a net work t hat uses STP t o provide backup links bet ween swit ches and also
perform s MLD snooping and proxy funct ions. MLD snooping- proxy, like MLD proxy, can m inim ize
MLD cont rol m essages and allow bet t er net work perform ance.
I n MLD snooping- proxy, if one upst ream port is learned via snooping, all ot her upst ream port s on
t he sam e device will be added t o t he sam e group. I f one upst ream port request s t o leave a group,
all ot her upst ream port s on t he sam e device will also be rem oved from t he group.
I n t he following MLD snooping- proxy exam ple, all connect ed upst ream port s ( 1 ~ 7) are t reat ed as
one int erface. The connect ion bet ween port s 8 and 9 is blocked by STP t o break t he loop. I f t here is
GS2210 Series User's Guide
187