IGMP and CGMP messages

ccnpninja

Hi folks,
I read that there are IGMP Join, Leave and Query messages. However I read that CGMP has Join, Leave and Query messages too.
Are they the same?
thanks.

scheistermeister

ccnpninja wrote:

Hi folks,
I read that there are IGMP Join, Leave and Query messages. However I read that CGMP has Join, Leave and Query messages too.
Are they the same?
thanks.

No they are not. CGMP works only with Cisco equipment. IGMP is the industry standard. Also the way they work is different. CGMP works with a router instructing a switch while IGMP is done on the switch itself.

tech-airman

ccnpninja wrote:

Hi folks,
I read that there are IGMP Join, Leave and Query messages. However I read that CGMP has Join, Leave and Query messages too.
Are they the same?
thanks.

ccnpninja,

The key word in IGMP is "Internet" which is the key word in "Internet Protocol" or IP for short. IP is a Layer 3 protocol. The key letter in CGMP is 'C' which is in the word switCh. SwitChes operate at Layer 2. So that's how I remember the difference between IGMP and CGMP.

APA

CGMP takes the inspection load off the switch as it is passed the messages from the router which has intercept join,leave and query messages.

IGMP is actually conducted by the switch itself and it intercepts join,leave and query messages sent\received can be hardware intensive.... No need for the router to pass on the messages.....

CGMP is cisco proprietary as well which means cisco router to cisco switch for the messages to be passed through.

scheistermeister

tech-airman wrote:

ccnpninja,

The key word in IGMP is "Internet" which is the key word in "Internet Protocol" or IP for short. IP is a Layer 3 protocol.

But that does not mean that a switch HAS (although it should) to be a Layer 3 device to identify IGMP packets. Just thought your explanation could be potential confusing.

If care is not taken as to how IGMP snooping is implemented, a switch may have to intercept all Layer 2 multicast packets to identify IGMP packets.

dtlokee

A router running CGMP doesn't do additional inspection of the IGMP messages since it receiving and processing them to allow multicast routing to function. What it does is to report the information regarding joins and leaves to the attached L2 switches.

Now, the preferred path is to use IGMP snooping since modern switches (L2 or L3) can do this function in hardware at wire speed and it does not impact the performance of the switch.

ccnpninja

Guys, here's what is written in Chris Bryant 's Study Guide:

When CGMP is first enabled on both the multicast router and switch, the
router will send a CGMP Join message, informing the switch that a
multicast router is now connected to it.

tech-airman

scheistermeister,

scheistermeister wrote:

tech-airman wrote:

ccnpninja,

The key word in IGMP is "Internet" which is the key word in "Internet Protocol" or IP for short. IP is a Layer 3 protocol.

But that does not mean that a switch HAS (although it should) to be a Layer 3 device to identify IGMP packets. Just thought your explanation could be potential confusing.

The OP asked...

ccnpninja wrote:

Are they the same?

My answer was an attempt at REDUCING confusion by INCREASING the DIFFERENCE between IGMP and CGMP by differentiating as Layer 3 and Layer 2 respectively. I didn't mention anything about equipment requirements. Equipment requirements if a Layer 2 or Layer 3 switch should be used depends on the existing network, network design goals, and other factors that are involved.

So I believe your post may be an irrelevant confusion increaser.

ccnpninja

I found an answer from a CCIE,
IGMP has Join, Leave and Query. However, CGMP has only Join and Leave. And they are different.
CGMP:
When the router gets an IGMP Join (Report) message from a host wanting to join a multicast group, he sends a CGMP Join, along with the Group Destination Address (i.e. the MAC address of the multicast group) and the Client Destination Address (host's MAC). So the switch forwards the multicast traffic of that group to the appropriate port (by reading its CAM table).
The same thing with CGMP Leave. The switch won't forward the unwanted multicast traffic out the "leaving" port, and still forwards it out the ports where there are hosts interested in it.

HTH.

networker050184

ccnpninja wrote:

I found an answer from a CCIE,
IGMP has Join, Leave and Query. However, CGMP has only Join and Leave. And they are different.
CGMP:
When the router gets an IGMP Join (Report) message from a host wanting to join a multicast group, he sends a CGMP Join, along with the Group Destination Address (i.e. the MAC address of the multicast group) and the Client Destination Address (host's MAC). So the switch forwards the multicast traffic of that group to the appropriate port (by reading its CAM table).
The same thing with CGMP Leave. The switch won't forward the unwanted multicast traffic out the "leaving" port, and still forwards it out the ports where there are hosts interested in it.

HTH.

You got an answer from a CCIE a couple of lines up!