Here are some common multicast addresses. All of these are worth knowing for the CCNA.

This is by no means a comprehensive list — just some of the more noteworthy ones!

Common Multicast Addresses
PurposeIPv6 AddressIPv4 Address
All nodes/hosts
(Functions like a broadcast message)
All routersFF02::2224.0.0.2
All OSPF routersFF02::5224.0.0.5
All OSPF DRs/BDRsFF02::6224.0.0.6
All RIP routersFF02::9224.0.0.9
All EIGRP routersFF02::A224.0.0.10