ProCurve 8200zl Uživatelská příručka stáhnout pdf (Strana 111)

PIM-SM (Sparse Mode)

PIM-SM Operation and Router Types

page 4-65.) When completed, the switchover from the RPT to a shorter SPT

can reduce unnecessary traffic concentrations in the network and reduce

multicast traffic throughput delays.

Note that the switchover from RPT to SPT is not instantaneous. For a short

period, packets for a given multicast group may be received from both the

RPT and the SPT. Also, in some topologies, the RPT and the SPT to the same

edge router may be identical.

PIM-SM

Router “A”

PIM-SM

Router “B”

PIM-SM

Router “C”

PIM-SM

Router “D”

Source of

Multicast

Group “X”

Host “Y”

Designated Router

(DR) for Unicast Source of

Multicast Group “X”

Elected Bootstrap Router

for the Domain, and

Elected Rendezvous

Point (RP) for Supporting

Multicast Group “X”

In default PIM-SM operation, the STP path

activates and the RPT path drops off after

the first multicast packet for a group is

received via the Rendezvous Point (RP).

Intermediate

Router in

RPT Path for

Group “X”

Figure 4-2. Example PIM-SM Domain with SPT Active To Support a Host that Has

Joined a Multicast Group

Restricting Multicast Traffic to Rendezvous-Point

Trees (RPTs)

An alternate method to allowing the domain to use SPTs is to configure all of

the routers in the domain to use only RPTs. However, doing so can increase

the traffic load in the network and cause delays in packet delivery.

Maintaining an Active Route for Multicast Group Members

The edge router itself and any intervening routers on the active tree between

the members (receivers) of a multicast group and the DR for that group, send

periodic joins. This keeps the active route available for as long as there is a

multicast receiver requesting the group. When a route times out or is pruned,

the DR ceases to send the requested group traffic on that route.

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