Layer 2 Multicast Technique
In LAN there are three methods for LAN multicast optimization.
- CGMP: Cisco Group Multicast management protocol
- IGMP Snooping
- RGMP: Router-port group management Protocol
Let’s discuss these topics and its working
Cisco Group management protocol has following features:
- It is cisco propriety protocol
- It is used because switch does not understand IGMP message.
- Switch by default floods multicast traffic to all switch ports in broadcast domain. CGMP helps layer-2 switch to determine how to distribute multicast traffic to host and switch does not understand multicast address.
- CGMP enable router to communicate to switch switch port about layer-2 multicast MAC address through CGMP message and CGMP modify the CAM table for switch
- Only Router generates the CGMP message, switch only listen to CGMP message and to achieve this, CGMP must be enabled on both router and switch connection.
- Layer 3 switch acts as router for CGMP and on these switches CGMP can be enabled on layer 3 interface that connect to layer-2 switches.
- Destination Address of CGMP is well known CGMP multicast address 0x100:0cdd: dddd
- CGMP has two more Mac address: Group Destination MAC address and Unicast Source Address.
Working of CGMP:
There are two method related to working of CGMP.
CGMP join msg Process:
Below figure states the working of CGMP join process