07/26/99


     Configuring a Bidir-PIM capable router to run in all 3 modes
     ------------------------------------------------------------

A Bidir-PIM capable router can run in bidir-mode, sparse-mode, dense-mode 
or any combination of them. If a router is configured for bidir-mode but 
does not learn of a bidir capable RP it will operate in sparse-mode. If a 
bidir capable router learns of a bidir RP then the group range advertised 
by the RP will operate in bidir-mode. If the RP advertises any groups with
a negative prefix they will operate in dense-mode.

By default a bidir RP advertises all groups as bidir. An access group on the
RP can be used to specify a list of groups to be advertised as bidir. Groups 
with the "deny" clause will operate in dense-mode.

A different (non bidir) RP address needs to be specified for groups that
need to operate in sparse-mode. This is because a single access-list allows 
only "permit" or a "deny" clause.

Following example shows how to configure a bidir RP to run all 3 modes. 
224/8 and 227/8 are bidir groups, 225/8 is dense-mode and 226/8 is sparse- 
mode. Both the bidir RP and the sparse-mode RP are configured on one router 
using two different loopback interfaces.

    ip pim send-rp-announce Loopback0 scope 10 group-list 45 bidir
    ip pim send-rp-announce Loopback1 scope 10 group-list 46
    ip pim send-rp-discovery scope 10
  
    access-list 45 permit 224.0.0.0 0.255.255.255
    access-list 45 permit 227.0.0.0 0.255.255.255
    access-list 45 deny   225.0.0.0 0.255.255.255
  
    access-list 46 permit 226.0.0.0 0.255.255.255