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message exceeds the maximum transmission unit (MTU). In respect of such IP fragmentation, 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
bootstrap message fragments (BSMFs).
• After receiving a BSMF that contains the RP-set information of one group range, a non-BSR router
updates corresponding RP-set information directly.
• If the RP-set information of one group range is carried in multiple BSMFs, a non-BSR router updates
corresponding RP-set information after receiving all these BSMFs.
Because the RP-set information contained in each segment is different, loss of some IP fragments will not
result in dropping of the entire message.
Generally, a BSR performs BSM semantic fragmentation according to the MTU of its BSR interface.
However, the semantic fragmentation of BSMs originated because of learning of a new PIM neighbor is
performed according to the MTU of the outgoing interface.
The function of BSM semantic fragmentation is enabled by default. Devices not supporting this function
might deem a fragment as an entire message and learn only part of the RP-set information. Therefore, if
such devices exist in the PIM-SM domain, you need to disable the 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 public network PIM
view or VPN instance PIM
view.
pim [ vpn-instance
vpn-instance-name ]
N/A
3. Disable the BSM semantic
fragmentation function.
undo bsm-fragment enable
By default, the BSM semantic
fragmentation function is enabled.
Configuring administrative scoping
When administrative scoping is disabled, a PIM-SM domain has only one BSR. The BSR manages the
whole network. To manage your network more effectively and specifically, partition the PIM-SM domain
into multiple admin-scope zones. Each admin-scope zone maintains a BSR, which provides services for
a specific multicast group range. The global scope zone also maintains a BSR, which provides services
for all the remaining multicast groups.
Enabling administrative scoping
Before you configure an admin-scope zone, you must enable administrative scoping.
Perform the following configuration on all routers in the PIM-SM domain.
To enable administrative scoping:
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