224.0.1.40 and 224.0.1.39 in sparse mode

[Quang Do Xuan]

Hi all,

I have several routers running OSPF and fully formed PIM neighborship.

AutoRP was configured on one router (172.28.56.51) and also a static RP (10.0.0.6) was configured (it is a reachable IP address)

I did the "show ip mroute" on some first hop routers and observed 2 things:

1. Some routers are listing 224.0.1.40 and 224.0.1.39 as Dense Mode

(*, 224.0.1.40), 7w3d/stopped, RP 0.0.0.0, flags: DCL

(*, 224.0.1.39), 7w3d/stopped, RP 0.0.0.0, flags: DC

A "show ip pim rp mapping" resulted in:

RP 172.28.8.51 (?), v2v1

   Info source: 172.28.56.51 (?), elected via Auto-RP

        Uptime: 1w4d, expires: 00:02:22

2. Some other routers are listing 224.0.1.40 and 224.0.1.39 as Sparse Mode

(*, 224.0.1.39), 7w0d/00:02:51, RP 10.0.0.6, flags: SJC

(*, 224.0.1.40), 7w0d/00:03:03, RP 10.0.0.6, flags: SJCLF

A "show ip pim rp mapping" resulted in:

Group(s) 224.0.0.0/4

  RP 172.28.8.51 (?), v2v1

    Info source: 172.28.56.51 (?), elected via Auto-RP

         Uptime: 6d06h, expires: 00:02:55

Group(s): 224.0.0.0/4, Static

    RP: 10.0.0.6 (?)

First case is totally what I expected as 224.0.1.40 and 224.0.1.39 should operate in Dense Mode by default, and a Auto RP should override a static RP

On all routers, for all other groups, 172.28.56.51 wins over 10.0.0.6 to become RP

Configurations on all 1st hop routers are the same

Can anyone explain to me why that happened?

[Quang Do Xuan]

Sorry if I wasted your time guys

I just found out those which are listing the 2 groups as Sparse Mode were configured with the static RP 10.0.0.6

And Auto RP's behavior is to ignore the 2 groups 224.0.1.40 and 224.0.1.39 then it wins over static RP for all groups except these 2 which were left behind for the static RP 10.0.0.6

Static RP, on the other hand, take all groups and makes them Sparse Mode. (however has lower priority compared to Auto RP)

Regards