Ethan Banks Not writing about IT.

OECG – Chapter 20


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

Auto-RP – Cisco proprietary. Uses announce and discovery multicast messages to help routers learn who the rendezvous point is for specific multicast groups.

dense-mode protocol – a multicast protocol that presumes every segment wants to get all multicast traffic, unless pruned otherwise

designated router – the PIM router with the highest IP address on the segment

downstream router – the multicast router closer to the host.
DVMRP – distance vector multicast routing protocol – dense mode, uses its own unicast routing method kind of like RIP

graft message – sent by a PIM-DM router to the upstream router asking that multicast traffic for a specific group be delivered right away. Also: a note delivered by a Congressional page to his superior to let him know a new automobile has been unexpectedly delivered by a wealthy constituent.

graft ack message – unicast back to the sender of the graft message “Hey, I got your graft.” Also: a message relayed by a Congressman via page to a wealthy constituent saying, “The car is wonderful. Incidentally, I see the issue your way now. You can count on my vote.”

join/prune message – a PIM router uses these to tell the upstream router that it does or does not want to receive traffic for a specific multicast group

MOSPF – multicast OSPF – an extension of OSPF, cannot run without OSPF in fact. Uses LSA type 6 messages to build the SPF tree.

multicast scoping – determining how far away multicast traffic can go in your network

multicast state information – the mroute routing table entry

PIM-DM – functions independently of other routing protocols; this is the dense mode version, where all router segments will receive multicast group traffic by default.

PIM-SM – functions independently of other routing protocols; this is the sparse mode version, where no router segments will receive multicast group traffic by default.

PIM-SM (S, G) RP-bit Prune – used when a router changes from RPT (routed through the rendezvous point) to SPT (routed via best path back to the source). The prune message used has the RP bit set.

PIM Hello message – sent every 30 seconds, by default, to discover other PIM routers and form an adjacency

prune override – a 3 second timer used by an upstream router that’s received a prune message. If a join is received during that 3 seconds, the prune request will be overridden.

RP – rendezvous point – in PIM-SM, this is where multicast traffic for a group is first delivered.

RPF check – a multicast loop prevention mechanism. The reverse path forwarding check makes sure that the multicast traffic isn’t sent back out the interface it came in on.

shared distribution tree – traffic flow from the RP to the routers receiving multicast group traffic

shortest-path tree switchover – when a router no longer follows the path back to the RP, but rather back to the source of the multicast

source-based distribution tree – the way a dense-mode multicast routing protocol forwards multicast traffic – via the most efficient path back to the source

source DR – a designated router on the same segment as the multicast source

source registration – how a router encapsulated packets received from a new multicast source, forwarding them on via unicast to the RP

sparse-mode protocol – a multicast routing protocol that presumes no one wants to receive multicast traffic unless a join says they do.

TTL scoping – limits how far away a multicast packet can go. A router will only forward a multicast packet if the TTL value of the multicast router is less than or equal to the TTL value of the multicast packet.

upstream router – a router that’s forwarded a multicast packet to a downstream router. The upstream rotuer is closer to the multicast source.

By Ethan Banks
Ethan Banks Not writing about IT.

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