3.2.c [ii] SA filter
MSDP-SA messages contain Source, Group (S, G) information for rendezvous points (RPs) (also known as MSDP peers) in PIM sparse-mode (PIM-SM) domains. This mechanism allows RPs to learn about multicast sources in remote PIM-SM domains so that they can join those sources if there are local receivers in their own domain. You can also use MSDP between multiple RPs in a single PIM-SM domain to establish MSDP mesh-groups. With a default configuration, MSDP exchanges SA messages without filtering them for specific source or group addresses.
Typically, there are a number of (S, G) states in a PIM-SM domain that should stay within the PIM-SM domain, but, due to default filtering, they get passed in SA messages to MSDP peers. Examples of this include domain local applications that use global IP multicast addresses , and sources that use local IP addresses (such as 10. x.y.z). In the native IP multicast Internet, this default leads to excessive (S, G) information being shared.
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2570-2573). . Kindle Edition.