TP-Link T2700G-28TQ T2700G-28TQ User Guide V1 - Page 262

RP Discovering, DR Elect

Page 262 highlights

Figure 11-15 DR Elect As shown in Figure 11-15, the DR election process is illustrated below: (1) Routers in the shared network sends Hello message carrying DR-election priority to each other, and the router with the highest priority will be elected as the DR; (2) If the routers have the same priorities, or at least one route in the network doesn't support carrying the DR-election priority in the Hello packet, the routers with the highest IP address will be elected as the DR. When the DR fails, a new DR election process will be triggered if the other routers haven't received the hello packet from the DR before they time out.  RP Discovering RP is the core device in the PIM SM domain. In a small network with simple structure, the multicast data is so little that merely one RP is enough to forward it. In this network an RP can be statically designated among the routers in the PIM SM domain; in more circumstances, the PIM SM domain is of large scale and the forwarding data for the RP is huge. To release the burden of the RP and optimize the RPT topology, each multicast group should have its own RP. Thus the bootstrapping mechanism is needed to elect the RP dynamically. The BSR (BootStrap Router) should be configured in this mechanism. BSR is the administrative core in the PIM SM. It collects the Advertisement Messages sent from the C-RP (Candidate-RP) in the network and selects certain C-RP information to compose a RP-Set (which is the mapping relationship database between the multicast group and the RP). The RP-Set is published to the whole PIM SM domain and all the routers (including DR) can calculate the required RP location according to the information offered by the RP-Set. In a PIM SM domain (or administrative domain), there is only one BSR (for more details about BSR administrative domain, please refer to BSR Adminsitrative Domain) and several C-BSRs (Candidate-BSR). Once the BSR fails, a new BSR will be elected among the other C-BSRs to avoid business disruption. Similarly, several C-RPs can be configured in one PIM SM domain, and each multicast group's corresponding RP can be calculated through the BSR mechanism. The location of RP and BSR in the network is shown below: 250

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250
Figure 11-15 DR Elect
As shown in Figure 11-15, the DR election process is illustrated below:
(1) Routers in the shared network sends Hello message carrying DR-election priority to each
other, and the router with the highest priority will be elected as the DR;
(2) If the routers have the same priorities, or at least one route in the network doesn’t support
carrying the DR-election priority in the Hello packet, the routers with the highest IP address
will be elected as the DR.
When the DR fails, a new DR election process will be triggered if the other routers haven’t
received the hello packet from the DR before they time out.
RP Discovering
RP is the core device in the PIM SM domain. In a small network with simple structure, the
multicast data is so little that merely one RP is enough to forward it. In this network an RP can be
statically designated among the routers in the PIM SM domain; in more circumstances, the PIM
SM domain is of large scale and the forwarding data for the RP is huge. To release the burden of
the RP and optimize the RPT topology, each multicast group should have its own RP. Thus the
bootstrapping mechanism is needed to elect the RP dynamically. The BSR (BootStrap Router)
should be configured in this mechanism.
BSR is the administrative core in the PIM SM. It collects the Advertisement Messages sent from
the C-RP (Candidate-RP) in the network and selects certain C-RP information to compose a
RP-Set (which is the mapping relationship database between the multicast group and the RP).
The RP-Set is published to the whole PIM SM domain and all the routers (including DR) can
calculate the required RP location according to the information offered by the RP-Set.
In a PIM SM domain (or administrative domain), there is only one BSR (for more details about
BSR administrative domain, please refer to
BSR Adminsitrative Domain
) and several C-BSRs
(Candidate-BSR). Once the BSR fails, a new BSR will be elected among the other C-BSRs to
avoid business disruption. Similarly, several C-RPs can be configured in one PIM SM domain, and
each multicast group’s corresponding RP can be calculated through the BSR mechanism. The
location of RP and BSR in the network is shown below: