Configuration Guide User guide
FastIron Configuration Guide 1581
53-1002494-02
DVMRP overview
Pruning a multicast tree
After the multicast tree is constructed, pruning of the tree will occur after IP multicast packets
begin to traverse the tree.
As multicast packets reach leaf networks (subnets with no downstream interfaces), the local IGMP
database checks for the recently arrived IP multicast packet address. If the local database does
not contain the address (the address has not been learned), the router prunes (removes) the
address from the multicast tree and no longer receives multicasts until the prune age expires.
In Figure 178, Router 5 is a leaf node with no group members in its local database. Consequently,
Router 5 sends a prune message to its upstream router. This router will not receive any further
multicast traffic until the prune age interval expires.
FIGURE 178 Downstream broadcast of IP multicast packets from source host
FIGURE 179 Pruning leaf nodes from a multicast tree
...
...
...
229.225.0.1
Group
Member
Group
Member
Video Conferencing
Server
(207.95.5.1, 229.225.0.1)
(Source, Group)
229.225.0.1
Group
Member
Group
Member
Group
Member
Group
Member
Group
Member
Group
Member
229.225.0.1
Leaf Node
Leaf Node
Leaf Node
(No Group Members)
Intermediate Node
(No Group Members)
R2
R1
R3
R4
R5
R6