78
Disabling BSM semantic fragmentation
Generally, a BSR periodically distributes the RP-set information in bootstrap messages within the
BIDIR-PIM 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 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. Devices not supporting this function
might deem a fragment as an entire message, thus learning only part of the RP-set information. Therefore,
if such devices exist in the BIDIR-PIM 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 BIDIR-PIM domain has only one BSR. The BSR manages the
whole network. To manage your network more effectively and specifically, you can divide the BIDIR-PIM
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 rest
multicast groups.
Enabling administrative scoping
Before you configure an admin-scoped zone, you must enable administrative scoping first.
Perform the following configuration on all routers in the BIDIR-PIM domain.
To enable administrative scoping:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
