Hello Vadim
Yes, that is correct. The process of choosing the RP is something that is done independently for each group. Also, each individual mapping agent independently and individually makes these decisions regardless of what other mapping agents do. As stated in this Cisco documentation:
The mapping agent receives announcements of intention to become the RP from Candidate-RPs. The mapping agent then announces the winner of the RP election. This announcement is made independently of the decisions by the other mapping agents.
In addition, when there are multiple mapping agents, conflicts are resolved following these rules:
- If there are two announcements with the same group range but different RPs, the mapping agent will select the announcement with the highest RP IP address.
- If there are two announcements where one group is a subset of another but the RPs are different, both will be sent.
- All other announcements are grouped together without any conflict resolution.
Now mapping agents send out their conclusions based on these rules to the 224.0.1.40 multicast group, to which all regular routers join. Based on this content, each router is responsible for populating its own Auto-RP cache with the Group to RP mappings. The cache contains both negative and positive entries.
When looking for an RP for a particular group, the Auto-RP algorithm will look through the negative entries. If there is a match to a negative entry, no RP is used, and the group is considered to operate in dense mode. Any RP information in the negative entries will be ignored since RPs are not used in dense mode.
If the group does not match a negative entry, the algorithm will begin to search in the positive list.
Now in this list, because each group corresponds to a particulate RP, there may be conflicts where multiple RPs try to serve overlapping group ranges. The receiving router uses the longest match rule to resolve all conflicts. If there are multiple matches, only the one with the longest prefix length is selected.
So you see, any conflicts, even due to malicious misinformation given by a rogue mapping agent, are ultimately resolved within each multicast router with very specific criteria.
I hope this has been helpful!
Laz