Hi Donald,
 
I've restartet the FRR in colo1. Now I can see the pimreg in colo1 and colo2, which was missing in colo1 last time.
But now I have a missing mroute in colo1, whereas colo2 can see the mroute ... 
 
>`show ip multicast`
Colo1:
-----
Mroute socket descriptor: 7(Default-IP-Routing-Table)
Mroute socket uptime: 00:02:47
Zclient update socket: 10 failures=0
Zclient lookup socket: 13 failures=0
Maximum highest VifIndex: 31
Upstream Join Timer: 60 secs
Join/Prune Holdtime: 210 secs
PIM ECMP: Disable
PIM ECMP Rebalance: Disable
RPF Cache Refresh Delay:    50 msecs
RPF Cache Refresh Timer:    0 msecs
RPF Cache Refresh Requests: 2
RPF Cache Refresh Events:   2
RPF Cache Refresh Last:     00:01:40
Nexthop Lookups:            3
Nexthop Lookups Avoided:    0
Scan OIL - Last: 00:01:40  Events: 2
MFC Add  - Last: --:--:--  Events: 0
MFC Del  - Last: --:--:--  Events: 0
Interface Address            ifi Vif  PktsIn PktsOut    BytesIn   BytesOut
Colo1:Colo2  172.21.21.75     16   0       0       0          0          0
ens4f1.308   172.22.190.10    12   0       0       0          0          0
pimreg       0.0.0.0          18   0       0       0          0          0

Colo2:
-----
Mroute socket descriptor: 7(Default-IP-Routing-Table)
Mroute socket uptime: 47:36:45
Zclient update socket: 10 failures=0
Zclient lookup socket: 13 failures=0
Maximum highest VifIndex: 31
Upstream Join Timer: 60 secs
Join/Prune Holdtime: 210 secs
PIM ECMP: Disable
PIM ECMP Rebalance: Disable
RPF Cache Refresh Delay:    50 msecs
RPF Cache Refresh Timer:    0 msecs
RPF Cache Refresh Requests: 22
RPF Cache Refresh Events:   18
RPF Cache Refresh Last:     00:01:13
Nexthop Lookups:            769
Nexthop Lookups Avoided:    0
Scan OIL - Last: 00:01:13  Events: 18
MFC Add  - Last: 00:00:13  Events: 28
MFC Del  - Last: 00:01:13  Events: 385
Interface Address            ifi Vif  PktsIn PktsOut    BytesIn   BytesOut
Colo2:Colo1  172.21.21.76     21   0       0   27155          0   38361631
eth0         172.24.37.3       2   1   27155       0   38361631          0
pimreg       0.0.0.0          45   0       0   27155          0   38361631
>`show ip pim upstream`
Colo1:
-----
Iif       Source          Group           State       Uptime   JoinTimer RSTimer   KATimer   RefCnt
Colo1:Colo210.55.0.33      232.122.14.42   J           00:01:18 00:00:42  --:--:--  --:--:--       1
Colo2:
-----
Iif       Source          Group           State       Uptime   JoinTimer RSTimer   KATimer   RefCnt
eth0      10.55.0.33      232.122.14.42   J           00:01:41 00:00:44  --:--:--  --:--:--       1
>`show ip mroute`
Colo1:
-----
Source          Group           Proto  Input      Output     TTL  Uptime

Colo2:
-----
Source          Group           Proto  Input      Output     TTL  Uptime
10.55.0.33      232.122.14.42   PIM    eth0       FR2HKX     1    00:02:37

> cat /proc/net/ip_mr_cache
Colo1:
------
Group    Origin   Iif     Pkts    Bytes    Wrong Oifs

Colo2:
-----
Group    Origin   Iif     Pkts    Bytes    Wrong Oifs
2A0E7AE8 2100370A 1         30    44940        0  0:1

greetings,
Jonas