CCIE Candidate

05/02/2007 - 1.5 hours. Complete Ch. 16 write-up and definitions.
05/05/2007 - 3.0 hours. Complete Ch. 17 write-up and definitions in one shot. Ow.
05/07/2007 - 2.0 hours. Complete Ch. 18 write-up and definitions. And tomorrow I can start in on the next juggernaut - multicasting.
05/09/2007 - 2.0 hours. Purchased “TESTiT” from netmasterclass.com. [...]

administrative scoping - limits what routers will receive multicast traffic on the 239.xx.xx.xx range be applying a filter to an interface.
assert message - PIM routers use these to determine which one will forward traffic for a particular multicast group onto a segment by comparing administrative distance and metric back to the multicast source

In the previous post, it was mentioned that you can statically assign the RP, so that PIM-SM routers know where it is. And that’s about as exciting as doing a static route. Icky. Of course, you can dynamically discover RPs, as well as configure redundant RPs. (Side note - I’ve worked [...]

The last post on Protocol Independent Multicast Sparse Mode would have been way too long if I’d kept it going…so it continues here.
Various PIM-SM Behaviors

PIM-SM routes are in the context of returning to the rendezvous point, not the source. This forms a shared distribution tree, or root-path tree, with the tree root at the [...]

The book mentions 2 sparse-mode multicast routing protocols: Protocol Independent Multicast Sparse Mode (PIM-SM) and Core-Based Tree (CBT). Looking ahead in the chapter, I don’t see any further mention of CBT…so off we go with PIM-SM.
PIM-SM is similar in core functionality to PIM-DM, with one major exception. Whereas PIM-DM assumes everyone wants [...]

The book spends all of a single page discussing the 2 multicast routing protocols DVMRP & MOSPF. So I won’t belabor them beyond these notes in the book
Distance Vector Multicast Routing Protocol (DVMRP) - RFC 1075

IOS doesn’t support full-blown DVMRP, although you can hook up an IOS router to a DVMRP network.

In local area networks (i.e. multiaccess networks versus point-to-point links), there are three areas the book touches on that are notable.
Prune Override

In a LAN scenario, it’s possible to have several routers sharing a network segment.

The book spends the most time on Protocol Independent Multicast Dense Mode (PIM-DM), with barely a mention of the other dense mode multicast routing protocols DVMRP and MOSPF. I’ll cover PIM-DM in this post, and the other 2 in another post before moving on to sparse mode multicast routing protocols.
PIM-DM

PIM was Cisco proprietary, but [...]

Multicast routing is fundamentally different from unicast routing in that multicast destinations are not stored in the routing table. The router doesn’t keep a list of all hosts that have enrolled in a multicast group. So when a router receives a packet destined for a multicast address, how does the router make its [...]

administratively scoped addresses - 239.0.0.0 through 239.255.255.255; used for private network multicasting
CGMP - Cisco group management protocol. Used by a router to inform a switch of multicast MACs it should add or remove from its CAM table. The switch then knows which ports to forward multicast traffic to, rather than flooding to all [...]

Router-Port Group Management Protocol (RGMP) restricts the multicast destinations that a switch will forward to a router. This is intended to reduce router overhead. RGMP and CGMP, both Cisco proprietary, are mutually exclusive. Enabling one disables the other. RGMP does work with IGMP snooping, however. Remember that while IGMP snooping [...]

IGMP snooping is appropriate when you are not an end-to-end Cisco shop. Remember that CGMP is Cisco proprietary, although many Cisco switches support IGMP snooping as well as CGMP. A switch engaged in IGMP snooping does what it sounds like - it eavesdrops on the IGMP conversion between hosts and routers.
IGMP Snooping - [...]

Now we move away from the host-to-router interaction, and review the role that switches play in the world of multicast routing. While IGMP tells a router what LAN ports it should be forwarding multicast traffic through, IGMP doesn’t do a thing for switches. Other functions such as Cisco Group Management Protocol (CGMP), IGMP [...]

The book points out that IGMPv3 is a major protocol change, and implementing it is A Very Big Deal. Some major IGMPv3 points:

IGMPv3 allows hosts to control who is sending traffic to their group by filtering the source address. This is known a Source-Specific Multicast (SSM). This a DoS mitigation control.
How would [...]

IGMPv2 Host with IGMPv1 Routers

An IGMPv2 host normally sends a report with a message type of 0×16. This is not a message type understood by an IGMPv1 router. Therefore, the IGMPv2 needs a mechanism to recognize when the router on his segment is only IGMPv1 capable.