nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

*via 10.1.0.2, Eth4/1, [250/0], 04:11:21, am
N7K-1-Core1# show ip route 10.1.0.2
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%' in via output denotes VRF
10.1.0.2/32, ubest/mbest: 1/1, attached
*via 10.1.0.2, Eth4/1, [250/0], 04:12:54, am
**via 10.1.0.30, [1/0], 00:01:32, mstatic
N7K-1-Core1#
IGMP Operation
Internet Group Management Protocol (IGMP) is an important component of a multicast
network. IGMP is the protocol used by a host to signal it wants to join a specific multicast
group. The router that sees the IGMP join message begins to send the multicast traffic
requested by the host to the receiver. IGMP has matured over time, and there currently are
three versions specified, named appropriately enough: IGMPv1, IGMPv2, and IGMPv3.
IGMPv1 is defined in the Internet Engineering Task Force (IETF) RFC 1112, IGMPv2 is
defined in RFC 2236, and IGMPv3 is defined in RFC 3376.
Note
Most modern operating systems use IGMPv3, although there are legacy systems that
do not yet support it.
IGMP works through membership reports, and at its most simple process, routers on a
network receive an unsolicited membership report from hosts that want to receive multicast
traffic. The router processes these requests and begins to send the multicast traffic to the
host until either a timeout value or a leave message is received.
IGMPv3 adds support for SSM, previously described in the chapter. In addition, IGMPv3
hosts do not perform report suppression like IGMPv1 and IGMPv2 hosts. IGMP report
suppression is a methodology in which the switch sends only one IGMP report per multicast
router query to avoid duplicate IGMP reports and preserve CPU resources.
IGMP works on routers that understand multicast traffic. For switches that might operate
only at Layer 2, a technology called IGMP snooping enables intelligent forwarding of
multicast traffic without broadcast or flooding behaviors. IGMP snooping enables a Layer 2
switch to examine, or snoop, IGMP membership reports and send multicast traffic only to
ports with hosts that ask for the specific groups. Without IGMP snooping, a typical Layer 2
switch would flood all multicast traffic to every port. This can be quite a lot of traffic and
negatively impact network performance.
IGMP Configuration on Nexus 7000