Chapter 24 Multicast
GS2210 Series User’s Guide
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IGMP Snooping
A Sw it ch can passively snoop on I GMP packet s t ransfer r ed bet w een I P m ult icast r out er s/ sw it ches
and I P m ult icast host s t o lear n t he I P m ult icast group m em ber ship. I t checks I GMP packet s passing
t hr ough it , picks out t he gr oup r egist rat ion infor m at ion, and configur es m ult icast ing accor dingly.
I GMP snooping allow s t he Sw it ch t o lear n m ult icast gr oups w it hout you having t o m anually
configure t hem .
The Swit ch for war ds m ult icast t raffic dest ined for m ult icast gr oups ( t hat it has lear ned fr om I GMP
snooping or t hat you have m anually configur ed) t o por t s t hat ar e m em ber s of t hat group. I GMP
snooping generat es no addit ional net w or k t raffic, allow ing you t o significant ly r educe m ult icast
t raffic passing t hr ough your Swit ch.
IGMP Snooping and VLANs
The Swit ch can per for m I GMP snooping on up t o 16 VLANs. You can configur e t he Sw it ch t o
aut om at ically lear n m ult icast gr oup m em ber ship of any VLANs. The Swit ch t hen perform s I GMP
snooping on t he fir st 16 VLANs t hat send I GMP packet s. This is referred t o as aut o m ode.
Alt er nat ively, you can specify t he VLANs t hat I GMP snooping should be per for m ed on. This is
r efer r ed t o as fixed m ode. I n fixed m ode t he Swit ch does not lear n m ult icast gr oup m em ber ship 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 Zy XEL- propriet ary feat ur e. I Pv6 MLD pr oxy allow s only one upst r eam
int er face on a sw it ch, w hile MLD snooping- pr ox y suppor t s m or e t han one upst r eam por t on a
sw it ch. The upst r eam por t in MLD snooping- pr ox y can r epor t gr oup changes t o a connect ed
m ult icast r out er and for war d MLD m essages t o ot her upst r eam por t s. This helps especially w hen
you want t o have a net wor k t hat uses STP t o pr ovide backup links bet ween sw it ches and also
per for m s MLD snooping and pr ox y funct ions. MLD snooping- pr oxy, like MLD pr ox y, can m inim ize
MLD cont r ol m essages and allow bet t er net w or k per for m ance.
I n MLD snooping- pr ox y, if one upst r eam por t is lear ned via snooping, all ot her upst r eam por t s on
t he sam e device w ill be added t o t he sam e gr oup. I f one upst r eam por t r equest s t o leave a gr oup,
all ot her upst r eam por t s on t he sam e device w ill also be r em oved fr om t he gr oup.
I n t he follow ing MLD snooping- pr oxy exam ple, all connect ed upst r eam por t s ( 1 ~ 7) ar e t r eat ed as
one int er face. The connect ion bet w een por t s 8 and 9 is blocked by STP t o br eak t he loop. I f t her e is
