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Disabling BSM semantic fragmentation
Generally, a BSR periodically distributes the RP-set information in bootstrap messages within the PIM-SM
domain. It encapsulates a BSM in an IP datagram and might split the datagram into fragments if the
message exceeds the 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
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 due to 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. A device that does not support this
function might regard a fragment as an entire message and learns 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:
Step 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-scoped zones. Each admin-scoped zone maintains a BSR, which serves a specific
multicast group range. The global-scoped zone also maintains a BSR, which serves all the remaining
multicast groups.
Enabling administrative scoping
Before you configure an admin-scoped zone, you must enable administrative scoping.
Perform the following configuration on all routers in the PIM-SM domain.
To enable administrative scoping:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
