Évaluations - 4, GPA: 4.5
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Figure 3-96 Service Policy Settings CLI - This example applies a service policy to an ingress interface. Console(config)#interface ethernet 1/5 4-143 Console(config-if)#service-policy input rd_policy#3 4-225 Console(config-if)# Multicast Filtering Multicast Filtering Multicasting is used to support real-time applications such as videoconferencing or streaming audio. A multicast server does not have to establish a separate connection with each client. It merely broadcasts its service to the network, and any hosts that want to receive the multicast register with their local multicast switch/ router. Although this approach reduces the Unicast Flow network overhead required by a multicast server, the broadcast traffic must be carefully pruned at Multicast every multicast switch/router it passes through to Flow ensure that traffic is only passed on to the hosts which subscribed to this service. This switch uses IGMP (Internet Group Management Protocol) to query for any attached hosts that want to receive a specific multicast service. It identifies the ports containing hosts requesting to join the service and sends data out to those ports only. It then propagates the service request up to any neighboring multicast switch/router to ensure that it will continue to receive the multicast service. This procedure is called multicast filtering. The purpose of IP multicast filtering is to optimize a switched network’s performance, so multicast packets will only be forwarded to those ports containing multicast group hosts or multicast routers/switches, instead of flooding traffic to all ports in the subnet (VLAN). This switch not only supports IP multicast filtering by passively monitoring IGMP query and report messages and multicast routing probe messages to register end-stations as multicast group members, but also supports the DVMRP and PIM-DM multicast routing protocols required to forward multicast traffic to other subnets (page 3-265 and 3-272). IGMP Protocol The Internet Group Management Protocol (IGMP) runs between hosts and their immediately adjacent multicast router/switch. IGMP is a multicast host registration protocol that allows any host to inform its local router that it wants to receive transmissions addressed to a specific multicast group. A router, or multicast-enabled switch, can periodically ask their hosts if they want to receive multicast traffic. If there is more than one router/switch on the LAN performing IP multicasting, one of these devices is elected “querier” and assumes the role of querying the LAN for group members. It then propagates the service requests on to any adjacent multicast switch/router to ensure that it will continue to receive the multicast service. Configuring the Switch Based on the group membership information learned from IGMP, a router/switch can determine which (if any) multicast traffic needs to be forwarded to each of its ports. At Layer 3, multicast routers use this information, along with a multicast routing protocol such as DVMRP or PIM, to support IP multicasting across the Internet. Note that IGMP neither alters nor routes IP multicast packets. A multicast routing protocol must be used to deliver IP multicast packets across different subnetworks. Therefore, when DVMRP or PIM routing is enabled for a subnet on this switch, you also need to enable IGMP. L3 -network core (multicast routing) L2 -edge switches (snooping and query) L2 switch to end nodes (snooping on IGMP clients) Layer 2 IGMP (Snooping and Query) IGMP Snooping and Query – If multicast routing is not supported on other switches in your network, you can use IGMP Snooping and IGMP Query (page 3-171) to monitor IGMP service requests passing between multicast clients and servers, and dynamically configure the switch ports which need to forward multicast traffic. Static IGMP Router Interface – If IGMP snooping cannot locate the IGMP querier, you can manually designate a known IGMP querier (i.e., a multicast router/switch) connected over the network to an interface on your switch (page 3-174). This interface will then join all the current multicast groups supported by the attached router/switch to ensure that multicast traffic is passed to all appropriate interfaces within the switch. Static IGMP Host Interface – For multicast applications that you need to control more carefully, you can manually assign a multicast service to specific interfaces on the switch (page 3-176). IGMP Query (Layer 2 or 3) – IGMP Query can only be enabled globally at Layer 2, but can be enabled for individual VLAN interfaces at Layer 3 (page 3-177). However, note that Layer 2 query is disabled if Layer 3 query is enabled. Multicast Filtering Configuring IGMP Snooping and Query Parameters You can configure the switch to forward multicast traffic intelligently. Based on the IGMP query and report messages, the switch forwards traffic only to the ports that request multicast traffic. This prevents the switch from broadcasting the traffic to...