Dense Mode
You should use Dense Mode for dense population of hosts and plentiful bandwidth
- DVMRP Distance Vector Multicast Routing Protocol
- Used frequently on the MBONE
- Uses reverse path flooding
- Periodic floodings to offer groups to new hosts
- Unicast path based on hop counts
- Cisco routers use PIM to unteract with DVMRP routers, but do not directly implement DVMRP
- PIMDM
Sparse Mode
- Use for a sparse distribution of multicast members
- assumes specific requests are used to join
- used when crossing WANs
Source:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/himc_c/mcbcncpt.htm#wp1077054