Configuring Basal Multicast Functionality with PIM-DM
Problem
You appetite to canyon multicast cartage through the router.
Solution
In a baby arrangement with few routers and almost ablaze multicast appliance bandwidth requirements, the easiest way to apparatus multicast acquisition is to use PIM-DM. This archetype shows the configurations for two routers that are affiliated through a Serial connection, both with FastEthernet interfaces to represent the LAN connections. It is important to accredit multicast acquisition on all interfaces that affix to added multicast-enabled routers or to multicast user or server segments.
The aboriginal router looks like this:
Router1#configure terminal
Enter agreement commands, one per line. End with CNTL/Z.
Router1(config)#ip multicast-routing
Router1(config)#interface FastEthernet0/0
Router1(config-if)#ip abode 192.168.1.1 255.255.255.0
Router1(config-if)#ip pim dense-mode
Router1(config-if)#exit
Router1(config)#interface Serial1/0
Router1(config-if)#ip abode 192.168.2.5 255.255.255.252
Router1(config-if)#ip pim dense-mode
Router1(config-if)#end
Router1#
And the additional router looks appreciably similar:
Router2#configure terminal
Enter agreement commands, one per line. End with CNTL/Z.
Router2(config)#ip multicast-routing
Router2(config)#interface FastEthernet0/0
Router2(config-if)#ip abode 192.168.3.1 255.255.255.0
Router2(config-if)#ip pim dense-mode
Router2(config-if)#exit
Router2(config)#interface Serial1/0
Router2(config-if)#ip abode 192.168.2.6 255.255.255.252
Router2(config-if)#ip pim dense-mode
Router2(config-if)#end
Router2#
Discussion
With this simple configuration, you get all of the basal multicast functionality. The routers will administer multicast packets properly, they will accept for end accessories to accompany and leave groups with IGMP (Version 1, 2, or 3), and they will amend one addition with advice about what multicast groups are currently in use as able-bodied as area the servers and accumulation associates are. For abounding types of multicast applications, this is all you need. But it is important to bethink that the PIM-DM agreement is alone adapted for assertive types of networks with almost specific multicast acquisition requirements.
First, PIM-DM works best in almost baby networks with no added than a few hops amid the sender and the best alien receiver. Second, the cardinal of multicast servers should be small, and the receivers should be broadcast throughout the arrangement in almost ample numbers. And third, because PIM-DM uses the multicast cartage itself to accumulate advice about area the servers are, it needs a abiding breeze of traffic. In particular, it's a bad abstraction to use PIM-DM with multicast applications that can abeyance added than three account amid packets because the routers will even the acquisition advice out of their tables and accept to clean these tables back the abutting packet is received.
If one or added of these altitude is not accurate for any of your multicast applications again you should apparently accede one of the added acquisition protocols, decidedly PIM-SM.
One final point to accede in any array of acquisition is how the router will about-face the packets. As we discussed in Chapter 11, you appetite to abstain action switching annihilation unless it's actually necessary. Fortunately, multicast packets are fast switched by default. However, in abounding configurations, it is accepted to attenuate multicast fast switching. So it is a acceptable abstraction to attending at your router configurations and accomplish abiding that you don't accept any multicast interfaces that accommodate the account no ip mroute-cache. If any interfaces do accept this command, again you should re-enable the adopted absence fast switching behavior by application the interface akin command ip mroute-cache. This is accurate behindhand of which multicast acquisition agreement you use.