4000 Router Series IP Multicast Configuration Guide

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Ste

Command

Remarks

3. Configure a PIM domain

border.

pim bsr-boundary

By default, no PIM domain border

is configured.

Disabling the BSM semantic fragmentation function

Generally, a BSR periodically advertises the RP-set information in BSMs within the PIM-SM domain. It

encapsulates a BSM in an IP datagram and might fragment the datagram if the message exceeds the

MTU. In this case, loss of a single IP fragment leads to unavailability of the entire message.

Semantic fragmentation of BSMs can solve this issue. When a BSM exceeds the MTU, it is split to multiple

BSM fragments (BSMFs).

• If the RP-set information for a multicast group range is carried in one BSMF, a non-BSR router directly

updates the RP-set information for the group range after receiving the BSMF.

• If the RP-set information for a multicast group range is carried in multiple BSMFs, a non-BSR router

updates the RP-set information for the group range after receiving all these BSMFs. Because the

RP-set information contained in each segment is different, loss of some IP fragments does not result

in dropping of the entire BSM.

The BSM semantic fragmentation function is enabled by default. A device that does not support this

function might regard a fragment as a BSM and thus learns only part of the RP-set information. Therefore,

if such devices exist in the PIM-SM domain, you must disable the BSM semantic fragmentation function on

the C-BSRs.

To disable the BSM semantic fragmentation function:

Ste

Command

Remarks

1. Enter system view.

system-view N/A

2. Enter PIM view.

pim [ vpn-instance

vpn-instance-name ]

N/A

3. Disable the BSM semantic

fragmentation function.

undo bsm-fragment enable

By default, BSM semantic

fragmentation is enabled.

NOTE:

Generally, a BSR performs BSM semantic fragmentation according to the MTU of its BSR interface.

However, for BSMs originated due to learning of a new PIM neighbor, semantic fragmentation is

performed according to the MTU of the interface that sends the BSMs.

Configuring multicast source registration

In a PIM-SM domain, the source-side DR sends register messages to the RP, and these register messages

have different multicast source or group addresses. You can configure a filtering rule to filter register

messages so that the RP can provide services for specific multicast groups. If the filtering rule denies an

(S, G) entry, or if the filtering rule does not define the action for this entry, the RP sends a register-stop

message to the DR to stop the registration process for the multicast data.

In view of information integrity of a register message in the transmission process, you can configure the

device to calculate the checksum based on the entire register message. However, to reduce the workload

of encapsulating data in register messages and for the sake of interoperability, do not use this checksum

calculation method.