cols for host membership of multicast groups. When running multicast at
layer 2, things get a little complicated for the switch. It doesn't know which
packets are membership report messages or which are actual multicast group
data packets because all of them have the same MAC address. Cisco Group
Management Protocol (CGMP) was implemented to fill this void. It runs on
both routers and switches.
address mapped to the MAC multicast address.
the host. It allows the host to send multicast membership reports to the
multicast router--the multicast router can also be a Route Switch Module
(RSM) or Multilayer Switch Feature Card (MSFC)--and still tell the
switch which port needs to receive the multicast data using the USA.
any ports that need to receive multicast data, CGMP will inform the router
that it doesn't need to forward multicast group data out the router interface.
that CGMP is used between the router and switch. When switches are
involved, the IGMP requests must be translated to CGMP and passed on to
the switch. These processes include the following:
nects to use it. When a host sends an IGMP report (membership report)
advertising membership of a multicast group, the message is forwarded to
the router (i.e., an actual multicast router, RSM, or an MSFC) for process-
ing. The router sees the request and processes it accordingly. The multicast
group is set up, and the two MAC addresses are generated. The router then