PIM sparse mode and auto-rp
Has anyone noticed any peculiarity with auto-rp and sparse mode. I
expected that even though by default 18.104.22.168 and 22.214.171.124 are in
dense mode, a mapping agent will only send the RP mappings to adjacent
neighbors and that's why one could get away with auto-rp and sparse
mode by having the MA and C-RP directly connected (or on the same
router) and the MA connected to other PIM routers.
With a topology as shown below, in which all the routers are setup for
sparse mode, I was able to see the RP mappings on R2, R3 and R1 but
not on R5 and R6. I understand typically I should use sparse-dense
mode or autorp listener with sparse or even use autorp with sparse and
static default RP but I just wanted to further understand how the RP-
announce and discovery groups work in sparse mode by default.
R4 was setup as C-RP and MA and I had the PIM nbma mode on R1's
physical interface. R5 is using a point-to-point subinterface for
connection to R1 and same goes for R2 over the frame relay network.
All other links are ethernet. Is it something about sparse mode with
autorp and serial point-to-point interfaces that is different over