Which multicast group is used for all PIM routers?

http://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml

Local Network Control Block (224.0.0.0 – 224.0.0.255 (224.0.0/24))

Registration Procedure(s)
Expert Review, IESG Approval, or Standards Action
Reference
[RFC5771]
Note
(*) It is only appropriate to use these values in explicitly-
configured experiments; they MUST NOT be shipped as defaults in
implementations. See [RFC3692] for details.
Available Formats

CSV
Address(es) Description References Date Registered Last Reviewed
224.0.0.0 Base Address (Reserved) [RFC1112][Jon_Postel]
224.0.0.1 All Systems on this Subnet [RFC1112][Jon_Postel]
224.0.0.2 All Routers on this Subnet [Jon_Postel]
224.0.0.3 Unassigned [Jon_Postel]
224.0.0.4 DVMRP Routers [RFC1075][Jon_Postel]
224.0.0.5 OSPFIGP OSPFIGP All Routers [RFC2328][OSPF_WG_Chairs]
224.0.0.6 OSPFIGP OSPFIGP Designated Routers [RFC2328][OSPF_WG_Chairs]
224.0.0.7 ST Routers [RFC1190][Karen_Seo]
224.0.0.8 ST Hosts [RFC1190][Karen_Seo]
224.0.0.9 RIP2 Routers [RFC1723][Gary_S_Malkin]
224.0.0.10 IGRP Routers [Dino_Farinacci] 1996-03-01
224.0.0.11 Mobile-Agents [[Bill Simpson]]
224.0.0.12 DHCP Server / Relay Agent [[Unknown]]
224.0.0.13 All PIM Routers [Dino_Farinacci] 1996-03-01