IP layer and layer 2 IGMP Snooping
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Posted by vicky on June 7, 2008, 1:28 am
Please log in for more thread options What is the difference in IP Layer IGMP Snooping and, Layer 2 IGMP Snooping. Thanks in advance. Vikrant | |||||||||||||||||||||||||
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Posted by Albert Manfredi on June 7, 2008, 4:48 pm
Please log in for more thread options > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Layer 2=
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 | |||||||||||||||||||||||||
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Posted by Albert Manfredi on June 8, 2008, 12:57 pm
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> =A0 =A0 =A0What is the difference in
r IGMP Snooping =A0and,
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0IP Laye= > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Layer 2=
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 | |||||||||||||||||||||||||
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Posted by vicky on June 11, 2008, 2:50 am
Please log in for more thread options >
> > =A0 =A0 =A0What is the difference in
>
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0IP La=
yer IGMP Snooping =A0and,
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Layer=
2 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 ----------------------------------------------------- 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 | |||||||||||||||||||||||||
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Posted by vicky on June 11, 2008, 2:55 am
Please log in for more thread options >
> > > > > > > > =A0 =A0 =A0What is the difference in
>
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0IP =
Layer IGMP Snooping =A0and,
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Lay=
er 2 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
>
> ----------------------------------------------------- > Ok Mr. Bert > > As u written that there may be some ambiguty =A0when (Multicast)IP to > Mac resolution > Is this ambiguity is > for example there are two multicast ip addresses > > 224.1.1.3 =A0- =A0 01-00-5e-01-01-03 > 225.1.1.3 =A0- =A0 01-00-5e-01-01-03 > > these represent 2 different multicast group. > > Now when it resoluted to =A0ip-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 =A0and =A0 225.1.1.3 ) > > please tell me .................... > > Thanks > > Vikrant- Hide quoted text - > > - Show quoted text - ----------------------------------------------------------------- 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 | |||||||||||||||||||||||||
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> =A0 =A0 =A0What is the difference in
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> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0IP Laye=