From: Jung-I Lin (easyman.lin@gmail.com)
Date: Thu Oct 12 2006 - 21:31:20 ART
Hi, STEELFIN
This command is introduced in ver 12.3(4)T.
You might not see this command in your IOS version 12.3(20).
As you can see this command is use to prevent "falling backup to
dense-mode".
What would cause a router falling back to dense-mode?
If the interface are in sparse-only-mode, it rely on RP(staticly or
dynamically) to join/transmit to the group.
If no RP exist for that group, then it is unable to join/transmit to the
group.
But if the interface is in sparse-dense-mode, it will switch the group to
dense-mode operation if the rp fails or not exist for that group.
The dm-fallback command is used in this situation, if you do not want the
router switch to dense-mode while the interface is configured in
"sparse-dense-mode".
You can issue "no ip pim dm-fallback". (This command is on by default)
Note this command will not affect the two "auto-rp" group
224.0.1.39/224.0.1.40.
These two group will always in dense-mode(if you configured sparse-dense-mod
on interfaces).
HTH.
On 10/13/06, STEELFIN <steelfin@gmail.com> wrote:
>
> Hi
>
> Is the "no ip pim dm-fallback" command used with sparse mode ? All of the
> documentation I read state that it is a command and should be entered on
> all
> sparse-mode routers to prevent fallback to dense mode in the event of RP
> failure.
>
> I am unable to enter this command :
>
> ROM: System Bootstrap, Version 12.2(7r) [cmong 7r], RELEASE SOFTWARE (fc1)
> ROM: C2600 Software (C2600-ADVENTERPRISEK9-M), Version 12.3(20), RELEASE
> SOFTWARE (fc2)
>
> R2(config)#no ip pim ?
> accept-register Registers accept filter
> accept-rp RP accept filter
> autorp Configure AutoRP global operations
> bidir-enable Enable Bidir-PIM
> bsr-candidate Candidate bootstrap router (candidate BSR)
> log-neighbor-changes Log PIM neighbor up/down and DR changes
> register-rate-limit Rate limit for PIM data registers
> register-source Source address for PIM Register
> rp-address PIM RP-address (Rendezvous Point)
> rp-announce-filter Auto-RP announce message filter
> rp-candidate To be a PIMv2 RP candidate
> send-rp-announce Auto-RP send RP announcement
> send-rp-discovery Auto-RP send RP discovery message (as RP-mapping
> agent)
> spt-threshold Source-tree switching threshold
> ssm Configure Source Specific Multicast
> state-refresh PIM DM State-Refresh configuration
> vrf Select VPN Routing/Forwarding instance
>
> Is this command no longer available?
>
> Thank you
>
> SF
>
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-- Thanks Best Regards,Jung-I Lin
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