Chapter 19

"Do I Know This Already?"

13.A and D


1.Reverse Path Forwarding (RPF) checks to make sure traffic always flows away from the root of the tree—from the source toward the recipients.
2.Protocol Independent Multicast (PIM) is a routing protocol that can be used for forwarding multicast traffic between IP subnets or network segments. PIM makes use of the IP unicast routing table and does not keep a separate multicast routing table.
3.PIM routers can be configured for dense mode. The source of the multicast traffic becomes the root of the tree, and the multicast tree is formed from the source to each of the recipients. This is also termed (S,G) multicast traffic, where the path between the source and group members is unique and well-defined.
4.With PIM sparse mode, the multicast tree is not extended to a router unless a host there has already joined the group. The multicast tree is built by beginning with the group members at the end-leaf nodes and extending back toward a central root point. The tree is grown in reverse, from the leaves toward the root.
5.If a group has an RP defined, sparse mode is used; otherwise, dense mode is used.
6.Auto-RP is a Cisco proprietary means of automatically informing PIM-SM routers of the appropriate RP for a group. This is done by identifying a centrally located and well-connected router to function as the mapping agent. The mapping agent learns of all candidate RPs that are announced over the Cisco-RP-Announce multicast address
7.PIMv2 uses a method similar to auto-RP. A bootstrap router (BSR) is identified; this router learns about RP candidates for a group and advertises them to PIM routers. You need to configure only the BSR and candidate RPs; all other PIM routers learn of the appropriate RP from the BSR.
8.Auto-RP is a PIMv1 function, whereas Bootstrap routers are used by PIMv2.
9.Enable Multicast Routing:
Router(config)#ip multicast-routing

Turn on PIM in appropriate mode on selected interfaces:

Router(config-if)#ip pim {dense-mode | sparse-dense-mode | sparse-mode}

Set up RPs:

Router(config)#ip pim send-rp-announce {interface type} {scope ttl} {group-list acl}


Router(config)#ip multicast-routing
Router(config)#interface s0/1
Router(config-if)#ip pim sparse-dense-mode
Router(config-if)#interface f0/0
Router(config-if)#ip pim sparse-dense-mode
Router(config-if)#interface s0/2
Router(config-if)#ip pim sparse-dense-mode

Router(config)#ip pim send-rp-announce f0/0 scope 5

12.Routes that are not source-specific (routes to an RP) are (*,G). Routes to a source are listed as (S,G).