26, what is RPF (Reverse Path Forwarding)?
A：Forwarding multicast traffic away from the source, rather than to the receiver, is called Reverse Path
Forwarding (RPF). This RPF check helps to guarantee that the distribution tree will be loop-free.
RPF is a key concept in multicast forwarding. It enables routers to correctly forward multicast traffic downstream
the distribution tree. RPF makes use of the existing unicast routing table to determine the upstream and
downstream neighbors. A router will forward a multicast packet only if it is received on the upstream interface.
27. what’s IOS command, you can see the output as below:
Neighbor address interface uptime/expire s ver DR Prio/mode
11.11.12.2 ethernet 0/0 00:00:05/00:01:39 V2 1/DR S
11.11.13.3 ethernet 0/1 00:00:05/00:01:39 V2 1/DR S
A：show ip pim neighbor
28.what about the EIGRP Administer Distance
A: 1.internal distance 90
2.external distance 170
3.summay distance 5
29. what’s IOS command , you can see the output as below
Neighbor ID Pri State Dead Time Address Interface
12.12.1.1 0 FULL/ - 00:00:37 12.12.1.1 Serial1/1
A: show ip ospf neighbor
30、BGP Administrative distance
A：BGP has a distance bgp command that allows you to set different administrative distances for three route
types: external,internal, and local.
External route 20
Internal route 200
Local route 200
