PIM tunnels are enabled automatically on routing platforms that have a tunnel PIC and on which you enable PIM sparse mode. You do not need to configure the tunnel interface.
PIM tunnels are unidirectional.
In PIM sparse mode, the first-hop routing platform encapsulates packets destined for the Rendezvous Point (RP) routing platform. The packets are encapsulated with a unicast header and are forwarded through a unicast tunnel to the RP. The RP then de-encapsulates the packets and transmits them through its multicast tree. To perform the encapsulation and de-encapsulation, the first-hop and RP routing platforms must be equipped with Tunnel PICs.
If you have a Tunnel PIC installed in your routing platform, you can configure IPv6-over-IPv4 tunnels. To do this, you configure a unicast tunnel across an existing IPv4 network infrastructure. IPv6 packets are encapsulated in IPv4 headers and sent across the IPv4 infrastructure through the configured tunnel. You manually configure configured tunnels on each end point.
PIM Tunnels (DR-to-RP)
branch#show ipv6 pim tunnel
Type : PIM Encap
RP : 2001:DB8:C003:1116::2
branch#show interface tunnel 1
Tunnel1 is up, line protocol is up
Hardware is Tunnel
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 2001:DB8:C003:111E::2 (Serial0/2),
Tunnel protocol/transport PIM/IPv6, key disabled,
Checksumming of packets disabled
Tunnel is transmit only
Last input never, output never, output hang never
Last clearing of “show interface” counters never
… output truncated…
PIM Tunnels (RP)
Source registering (on RP) – two virtual tunnels are created
- One transmit only for registering sources locally connected to the RP
- One receive only for decapsulation of incoming registers from remote designated routers
- No one-to-one relationship between virtual tunnels on designated routers and RP!