IP layer and layer 2 IGMP Snooping

Hi,,

What is the difference in

IP Layer IGMP Snooping and, Layer 2 IGMP Snooping.

Thanks in advance.

Vikrant

Reply to
vicky
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r IGMP Snooping =A0and,

IGMP Snooping.

There is no such thing as IP layer IGMP snooping.

IGMP snooping is something that the link layer does, in order to be more clever about forwarding MAC layer multicasts.

When the IP layer uses IGMP, it is not called snooping. If someone called it snooping, they are using confusing and inexact terminology.

Bert

Reply to
Albert Manfredi

r IGMP Snooping =A0and,

IGMP Snooping.

Wait, I think I know what this is referring to.

When doing IGMP snooping, the L2 switch can use the IP address of the IGMP join messages to derive the MAC multicast address, then use the MAC multicast address of the arriving data frames to make forwarding decisions. This is the more "classic" approach. Or the L2 switch can use the IP address of the arriving UDP/IP datagrams to make the forwarding decision, and never bother using the MAC multicast address at all.

Perhaps this is what the terminology is referring to. Using the IP address to make forwarding decisions is actually preferable, because

28 bits of an IPv4 multicast address determine the multicast group. When mapped to the MAC address, only 23 bits are used to differentiate IPv4 multicast groups at the MAC layer, so there is some ambiguity as to what MAC hosts really want the multicast.

Bert

Reply to
Albert Manfredi

yer IGMP Snooping =A0and,

2 IGMP Snooping.

----------------------------------------------------- Ok Mr. Bert

As u written that there may be some ambiguty when (Multicast)IP to Mac resolution Is this ambiguity is for example there are two multicast ip addresses

224.1.1.3 - 01-00-5e-01-01-03 225.1.1.3 - 01-00-5e-01-01-03

these represent 2 different multicast group.

Now when it resoluted to ip-mac for multicast table entry in l 2 switch as well as to come at DA of multicast packet.

then how a switch can able to differentiate the two multicast ranges (224.1.1.3 and 225.1.1.3 )

please tell me ....................

Thanks

Vikrant

Reply to
vicky

Layer IGMP Snooping =A0and,

er 2 IGMP Snooping.

-----------------------------------------------------------------

One more thing i want to ask

Is the Multicast IP to mac resolution is done at host pc's end also. to make a multicast MAC address

For exp if multicast ip address is

227.2.3.7

then its mac address

01-00-5e-02-03-07

is made at host pc end , as then it send packet by setting this mac address to the DA field.

Vikrant

Reply to
vicky

If the L2 switch uses the MAC multicast DA to decide which ports to forward the frame to, then it cannot differentiate between those two IP multicast groups. So the L2 switch sends frames from both of those IP multicast groups to all hosts that have joined one or the other (or both).

It is then the responsibility of the IP stack of the hosts to filter the incoming UDP/IP packets, based on the IP Class D address.

Bert

Reply to
Albert Manfredi

In transmission, and in reception. Yes. As explained in RFC 1112.

Bert

Reply to
Albert Manfredi

----------------------------------------------------------------------------=

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My new query is related to registration in a mulicasting group so for i m taking a case

For exp

register in another multicasting group

at one time another send its group registration in an another time)

so registration for different multicast group is sent by hosts is some before

So my question is if by one host the registration is sent some hours before as well as by anther one is few minutes before the fix time of multicast data is flow by router , so how the layer 2 switch manages there (hosts) table ?

Vikrant

Reply to
vicky

ill register in another multicasting group

uest at one time another send its group

The IGMP snooping switch must send "join" messages to the router if there is at least one host connected to that switch wants to join the multicast group. So as soon as that first host joins, the multicasts reach the switch.

But the snooping switch also keeps track of each individual host that indicates it wants to join the group, and only forwards the multicast packets on THOSE ports. And it also keeps track of the leave messages, to stop forwarding to particular switch ports.

So, no problem if hosts join late or leave early.

Read

formatting link
Bert

Reply to
Albert Manfredi

r will register in another multicasting group

request at one time another send its group

---------------------------------------------------------------------------=

------------------

Hello

Can u plz tell me about the DA (Destination Mac Address) and SA (Source mac Address)

of a frame which contains multicast data (or multicast member ship requist or leave requist)

is at this case is DA =3D=3D SA or SA contain a unique mac address of either router or host.

Please tell me

Thanks in advance

Vikrant

Reply to
vicky

will register in another multicasting group

equest at one time another send its group

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Hello Sir

can u plz tell me about

IGMP and GMRP

and if we r using IGMP Snooping at l2 switch , then we 've a requirment of GMRP also.

Thanks in advance

Vikrant

Reply to
vicky

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