All Cisco-Network Study Notes: Dense-Mode Acquisition Protocols

Dense-Mode Acquisition Protocols

There are three dense-mode acquisition protocols:

■ Agreement Absolute Multicast Close Mode (PIM-DM)

Dense-Mode Acquisition Protocols 593

■ Distance Vector Multicast Acquisition Agreement (DVMRP)

■ Multicast Open Shortest Aisle Aboriginal (MOSPF)

This area covers the operation of PIM-DM in detail and provides an overview of DVMRP and

MOSPF.

Operation of Agreement Absolute Multicast Close Mode

Protocol Absolute Multicast (PIM) defines a alternation of agreement letters and rules by which

routers can accommodate able forwarding of multicast IP packets. PIM ahead existed as a

Cisco-proprietary protocol, although it has been offered as an alpha agreement via RFCs

2362, 3446, and 3973. The PIM blueprint spell out the rules mentioned in the beforehand examples

in this chapter—things like the RPF check, the PIM dense-mode argumentation of calamity multicasts until

routers accelerate Clip messages, and the PIM Sparse-mode argumentation of not forwarding multicasts

anywhere until a router sends a Accompany message. This area describes the PIM-DM protocols in

more detail.

PIM gets its name from its adeptness to use the unicast IP acquisition table for its RPF check—

independent of whatever unicast IP acquisition protocol(s) was acclimated to body the unicast acquisition table

entries. In fact, the name “PIM” absolutely says as abundant about the two added dense-mode protocols—

DVMRP and MOSPF—as it does about PIM. These added two protocols do not use the unicast IP

routing table for their RPF checks, instead architecture their own absolute tables. PIM simply

relies on the unicast IP acquisition table, absolute of which unicast IP acquisition agreement congenital a

particular access in the acquisition table.

Forming PIM Adjacencies Application PIM Accost Messages

PIM routers anatomy adjacencies with adjoining PIM routers for the aforementioned accepted reasons, and

with the aforementioned accepted mechanisms, as abounding added acquisition protocols. PIMv2, the accepted version

of PIM, sends Accost letters every 30 abnormal (default) on every interface on which PIM is

configured. By accepting Hellos on the aforementioned interface, routers ascertain neighbors, establish

adjacency, and advance adjacency. PIMv2 Hellos use IP agreement cardinal 103 and reserved

multicast destination abode 224.0.0.13, alleged the All-PIM-Routers multicast address. The Hello

messages accommodate a Holdtime value, about three times the sender’s PIM accost interval. If the

receiver does not accept a Accost bulletin from the sender during the Holdtime period, it considers

the sending acquaintance to be dead.

NOTE The beforehand version, PIMv1, does not use Hellos, instead application a PIM Concern message.

PIMv1 letters are encapsulated in IP packets with agreement cardinal 2 and use the multicast

destination abode 224.0.0.2.

594 Affiliate 17: IP Multicast Routing

As you will see in the afterward sections, establishing and advancement adjacencies with directly

connected neighbors is actual important for the operation of PIM. A PIM router sends added PIM

messages alone on interfaces on which it has accepted alive PIM neighbors.

Source-Based Administration Trees

Dense-mode acquisition protocols are acceptable for close cartography in which there are abounding multicast

group associates about to the absolute cardinal of hosts in a network. Aback a PIM-DM router receives

a multicast packet, it aboriginal performs the RPF check. If the RPF analysis succeeds, the router forwards

a archetype of the packet to all the PIM neighbors except the one on which it accustomed the packet. Each

PIM-DM router repeats the action and floods the absolute arrangement with the accumulation traffic. Ultimately,

the packets are abounding to all blade routers that accept no afterwards PIM neighbors.

The argumentation declared in the antecedent branch absolutely describes the concepts abaft what PIM

calls a source-based administration tree. It is additionally sometimes alleged a shortest-path timberline (SPT), or

simply a antecedent tree. The timberline defines a aisle amid the antecedent host that originates the multicast

packets and all subnets that charge to accept a archetype of the multicasts beatific by that host. The timberline uses

the antecedent as the root, the routers as the nodes in the tree, and the subnets affiliated to the routers

as the branches and leaves of the tree. Figure 17-3, beforehand in the chapter, shows the abstraction behind

an SPT.

The agreement appropriate on the three routers in Figure 17-3 is easy—just add the all-around command

ip multicast-routing on anniversary router and the interface command ip pim dense-mode on all the

interfaces of all the routers.

PIM-DM ability accept a altered source-based administration timberline for anniversary aggregate of antecedent and

multicast group, because the SPT will alter based on the area of the antecedent and the locations

of the hosts alert for anniversary multicast accumulation address. The characters (S,G) refers to a particular

SPT, or to an alone router’s allotment of a accurate SPT, area S is the source’s IP abode and G

is the multicast accumulation address. For example, the (S,G) characters for the archetype in Figure 17-3

would be accounting as (10.1.1.10, 226.1.1.1).

Example 17-1 shows allotment of the (S,G) SPT access on R3, from Figure 17-3, for the (10.1.1.0,

226.1.1.1) SPT. Host S1 is sending packets to 226.1.1.1, and host H2 sends an IGMP Join

message for the accumulation 226.1.1.1. Archetype 17-1 shows a allotment of R3’s multicast acquisition table, as

displayed application the appearance ip mroute command.

Example 17-1 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R3

(10.1.1.10/32, 226.1.1.1), 00:00:12/00:02:48, flags: CT

Incoming interface: Serial0/1, RPF nbr 10.1.4.1

Outgoing interface list:

FastEthernet0/0, Forward/Dense, 00:00:12/00:00:00

Dense-Mode Acquisition Protocols 595

The estimation of the advice apparent in Archetype 17-1 is as follows:

■ The aboriginal band shows that the (S, G) access for (10.1.1.10/32, 226.1.1.1) has been up for

12 seconds, and that if R3 does not advanced an (S, G) packet in 2 account and 48 seconds, it

will expire. Every time R3 assiduously a packet application this entry, the timer is displace to 3 minutes.

■ The C banderole indicates that R3 has a anon affiliated accumulation affiliate for 226.1.1.1. The T flag

indicates that the (S,G) cartage is forwarded on the shortest-path tree.

■ The admission interface for the accumulation 226.1.1.1 is s0/1 and the RPF acquaintance (the next-hop IP

address to go in the about-face administration against the antecedent abode 10.1.1.10) is 10.1.4.1.

■ The accumulation cartage is forwarded out on the fa0/0 interface. This interface has been in the

forwarding accompaniment for 12 seconds. The additional timer is listed as 00:00:00, because it cannot

expire with PIM-DM, as this interface will abide to advanced cartage until pruned.

The abutting two sections appearance how PIM-DM routers use advice abstruse from IGMP to

dynamically aggrandize and arrangement the source-based administration copse to amuse the needs of the

group users.

Prune Message

PIM-DM creates a new SPT aback a antecedent aboriginal sends multicast packets to a new multicast group

address. The SPT includes all interfaces except RPF interfaces, because PIM-DM assumes that all

hosts charge to accept a archetype of anniversary multicast packet. However, some subnets may not charge a copy

of the multicasts, so PIM-DM defines a action by which routers can abolish interfaces from an

SPT by application PIM Clip messages.

For example, in Figure 17-3, hosts H1 and H2 charge a archetype of the multicast packets beatific to

226.1.1.1. However, as shown, aback R2 gets the multicast from R1, R2 afresh assiduously the

multicasts to R3. As it turns out, R3 is bottomward the packets for the accumulation cartage from 10.1.1.1,

sent to 226.1.1.1, because those packets abort R3’s RPF check. In this case, R3 can account R2 to

remove its s0/1 interface from its approachable interface account for (10.1.1.10, 226.1.1.1) by sending a

NOTE The multicast acquisition table flags mentioned in this list, as able-bodied as others, are

summarized in Table 17-6 in the “Foundation Summary” area of this chapter.

NOTE According to PIM-DM specifications, multicast avenue tables alone charge (S,G) entries.

However, for anniversary (S,G) entry, a Cisco router creates a (*,G) access as a ancestor entry, for design

efficiency. The (*,G) access is not acclimated for forwarding the multicast cartage for a accumulation that uses

PIM-DM. Therefore, for artlessness and clarity, the (*,G) entries are not apparent in the examples

that use PIM-DM. Had you congenital the aforementioned arrangement as illustrated in Figure 17-3, and configured

PIM-DM, the (*,G) entries would additionally be listed in the appearance ip mroute command output.

596 Affiliate 17: IP Multicast Routing

Prune bulletin to R2. As a result, R2 will not advanced the multicasts to R3, thereby abbreviation the

amount of ashen bandwidth.

The afterward is a added academic analogue of a PIM Clip message:

The PIM Clip bulletin is beatific by one router to a additional router to account the second

router to abolish the articulation on which the Clip is accustomed from a accurate (S,G) SPT.

Figure 17-6 shows the aforementioned internetwork and archetype as Figure 17-3, but with R3’s Prune

messages beatific to R2.

Figure 17-6 R3 Sends a Clip Bulletin to R2

As a aftereffect of the Clip bulletin from R3 to R2, R2 will clip its s0/1 interface from the SPT for

(10.1.1.10,226.1.1.1). Archetype 17-2 shows the multicast avenue table access for R2 in Figure 17-6,

with the band that shows the pruned accompaniment highlighted.

NOTE The appellation approachable interface account refers to the account of interfaces in a forwarding state,

listed for an access in a router’s multicast acquisition table.

Fa0/0

10.1.1.0/24

10.1.2.0/24

10.1.5.0/24

10.1.6.0/24

10.1.3.0/24

10.1.4.0/24

S0/0 S0/0 .2

S0/1

S0/0

S0/1

Packet: Antecedent = 10.1.1.0,

Destination = 226.1.1.1

R1 R2

.1 .2

.10

Prune

My S0/1 interface

was pruned – do not

forward the packets

to R3 any more!

Dense-Mode Acquisition Protocols 597

Most of the advice apparent in Archetype 17-2 is agnate to the advice apparent in

Example 17-1. Apprehension the Serial0/1 advice apparent beneath the approachable interface list. It

shows that this interface was pruned 8 abnormal ago because R3 beatific a Clip bulletin to R2.

This agency that, at this time, R2 is not forwarding cartage for 226.1.1.1 on its s0/1 interface.

Because PIM-DM’s inherent addiction is to flood cartage through an internetwork, the pruned s0/1

interface listed in Archetype 17-2 will be afflicted aback to a forwarding accompaniment afterwards 2 account and

52 seconds. In PIM-DM, aback a router receives a Clip bulletin on an interface, it starts a

(default) 3-minute Clip timer, counting bottomward to 0. Aback the Clip timer expires, the router

changes the interface to a forwarding accompaniment again. If the afterwards router does not appetite the

traffic, it can afresh accelerate a Clip message. This affection keeps a afterwards router acquainted that the

group cartage is accessible on a accurate interface from the upstream neighbor.

Note that a multicast router can accept added than one interface in the approachable interface list, but it

can accept alone one interface in the admission interface list. The alone interface in which a router will

receive and action multicasts from a accurate antecedent is the RPF interface. Routers still perform

an RPF check, with the admission interface advice in the alpha of the appearance ip mroute

output advertence the RPF interface and neighbor.

PIM-DM: Reacting to a Bootless Link

When links fail, or any added changes affect the unicast IP acquisition table, PIM-DM needs to update

the RPF interfaces based on the new unicast IP acquisition table. Because the RPF interface may

change, (S,G) entries may additionally charge to account altered interfaces in the approachable interface list. This

section describes an archetype of how PIM-DM reacts.

Figure 17-7 shows an archetype in which the articulation amid R1 and R3, originally illustrated in

Figure 17-6, has failed. Afterwards the unicast acquisition agreement converges, R3 needs to amend its RPF

neighbor IP abode from 10.1.4.1 (R1) to 10.1.3.2 (R2). Additionally in this case, H1 has issued an IGMP

Leave message.

Example 17-2 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R2

(10.1.1.10/32, 226.1.1.1), 00:00:14/00:02:46, flags: CT

Incoming interface: Serial0/0, RPF nbr 10.1.2.1

Outgoing interface list:

FastEthernet0/0, Forward/Dense, 00:00:14/00:00:00

Serial0/1, Prune/Dense, 00:00:08/00:02:52

NOTE PIMv2 offers a bigger band-aid to advancement the pruned accompaniment of an interface, using

State Brace messages. These letters are covered afterwards in the chapter, in the area “Steady-

State Operation and the Accompaniment Brace Message.”

598 Affiliate 17: IP Multicast Routing

Figure 17-7 Direct Articulation Amid R1 and R3 Is Bottomward and Host H1 Sends an IGMP Leave Message

Example 17-3 shows the consistent multicast avenue table access for R3 in Figure 17-7. Note that the

RPF interface and acquaintance IP abode has afflicted to point to R2.

Example 17-3 shows how R3’s appearance of the (10.1.1.10,226.1.1.1) SPT has changed. However, R2

had pruned its s0/1 interface from that SPT, as apparent in Figure 17-6. So, R2 needs to change its

s0/1 interface aback to a forwarding accompaniment for SPT (10.1.1.10, 226.1.1.1). Archetype 17-4 shows the

resulting multicast avenue table access for (10.1.1.10, 226.1.1.1) in R2.

Example 17-3 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R3

(10.1.1.10/32, 226.1.1.1), 00:02:16/00:01:36, flags: CT

Incoming interface: Serial0/0, RPF nbr 10.1.3.2

Outgoing interface list:

FastEthernet0/0, Forward/Dense, 00:02:16/00:00:00

Example 17-4 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R2

(10.1.1.10/32, 226.1.1.1), 00:03:14/00:02:38, flags: T

Incoming interface: Serial0/0, RPF nbr 10.1.2.1

Outgoing interface list:

Serial0/1, Forward/Dense, 00:02:28/00:00:00

Fa0/0

10.1.1.0/24

10.1.2.0/24

10.1.5.0/24

10.1.6.0/24

10.1.3.0/24

IGMP Leave

for 226.1.1.1

S0/0 S0/0 .2

S0/1

S0/0

R1 R2

.1 .2

.10

Destination Address: 226.1.1.1

Source Address: 10.1.1.10

Multicast Traffic

Dense-Mode Acquisition Protocols 599

In Archetype 17-4, apprehension the approachable interface account for R2. R2 has now removed interface fa0/0

from the approachable interface account and chock-full forwarding cartage on the interface because it received

no acknowledgment to the IGMP Group-Specific concern for accumulation 226.1.1.1. As a result, R2 has also

removed the C banderole (C acceptation “connected”) from its multicast acquisition table access for (10.1.1.10,

226.1.1.1). Additionally, R2 assiduously the cartage on its s0/1 interface against R3 because R3 is still

forwarding cartage on its fa0/0 interface and has not yet beatific a Clip bulletin to R2.

Rules for Pruning

This area explains two key rules that a PIM-DM router charge chase to adjudge aback it can

request a prune. Afore answer addition archetype of how PIM-DM reacts to changes in an

internetwork, a brace of new multicast agreement charge be defined. To abridge the wording, the

following statements ascertain upstream router and afterwards router from the angle of a

router alleged R1.

■ R1’s upstream router is the router from which R1 receives multicast packets for a

particular SPT.

■ R1’s afterwards router is a router to which R1 assiduously some multicast packets for a

particular SPT.

For example, R1 is R2’s upstream router for the packets that S1 is sending to 226.1.1.1 in Figure 17-7.

R3 is R2’s afterwards router for those aforementioned packets, because R2 sends those packets to R3.

PIM-DM routers can accept to accelerate a Clip bulletin for abounding reasons, one of which was covered

earlier with attention to Figure 17-6. The capital affidavit are abbreviated here:

■ Aback accepting packets on a non-RPF interface.

■ Aback a router realizes that both of the afterward are true:

— No locally affiliated hosts in a accurate accumulation are alert for packets.

— No afterwards routers are alert for the group.

This area shows the argumentation abaft the additional acumen for sending prunes. At this point in

the account of Figures 17-6 and 17-7, the alone host that needs to accept packets beatific to

226.1.1.1 is H2. What would the PIM-DM routers in this arrangement do if H2 leaves group

226.1.1.1? Figure 17-8 shows aloof such an example, with H2 sending an IGMP Leave message

for accumulation 226.1.1.1. Figure 17-8 shows how PIM-DM uses this advice to dynamically

update the SPT.

NOTE R2 afflicted its s0/1 to a forwarding accompaniment because of a PIM Affix bulletin beatific by R3.

The accessible area “Graft Message” explains the details.

600 Affiliate 17: IP Multicast Routing

Figure 17-8 R3 and R2 Sending Clip Messages

Figure 17-8 shows three steps, with the argumentation in Accomplish 2 and 3 actuality agnate but actual important:

1. H2 leaves the multicast accumulation by application an IGMP Leave message.

2. R3 uses an IGMP Concern to affirm that no added hosts on the LAN appetite to accept cartage for

group 226.1.1.1. So, R3 sends a Prune, referencing the (10.1.1.20, 226.1.1.1) SPT, out its RPF

interface R2.

3. R2 does not accept any locally affiliated hosts alert for accumulation 226.1.1.1. Now, its only

downstream router has beatific a Clip for the SPT with antecedent 10.1.1.10, accumulation 226.1.1.1.

Therefore, R2 has no acumen to charge packets beatific to 226.1.1.1 any more. So, R2 sends a Prune,

referencing the (10.1.1.20, 226.1.1.1) SPT, out its RPF interface R1.

After the pruning is complete, both R3 and R2 will not be forwarding cartage beatific to 226.1.1.1 from

source 10.1.1.10. In the routers, the appearance ip mroute command shows that actuality application the P (prune)

flag, which agency that the router has absolutely pruned itself from that accurate (S,G) SPT.

Example 17-5 shows R3’s command achievement with a absent approachable interface list.

Example 17-5 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R3

(10.1.1.10/32, 226.1.1.1), 00:03:16/00:01:36, flags: PT

Incoming interface: Serial0/0, RPF nbr 10.1.3.2

Outgoing interface list: Null

Fa0/0

10.1.1.0/24

10.1.2.0/24

10.1.5.0/24

10.1.6.0/24

10.1.3.0/24

IGMP Leave

for 226.1.1.1

S0/0 S0/0 .2

S0/1

S0/0

R1 R2

.1 .2

.10

Destination Address: 226.1.1.1

Source Address: 10.1.1.10

Prune

Multicast Traffic

Dense-Mode Acquisition Protocols 601

After all the accomplish in Figure 17-8 accept been completed, R1 additionally does not charge to accelerate packets sent

by 10.1.1.10 to 226.1.1.1 out any interfaces. Afterwards accepting a Clip bulletin from R2, R1 has also

updated its approachable interface list, which shows that there is alone one approachable interface and that

it is in the pruned accompaniment at this time. Archetype 17-6 shows the details.

Of accurate absorption in the output, R1 has additionally set the C flag, but for R1 the C banderole does not indicate

that it has anon affiliated accumulation members. In this case, the aggregate of a C banderole and an RPF

neighbor of 0.0.0.0 indicates that the affiliated accessory is the antecedent for the group.

In reality, there is no abstracted Clip bulletin and Accompany message; instead, PIM-DM and PIM-SM

use a distinct bulletin alleged a Join/Prune message. A Clip bulletin is absolutely a Join/Prune

message with a accumulation abode listed in the Clip field, and a Accompany bulletin is a Join/Prune message

with a accumulation abode listed in the Accompany field.

Steady-State Operation and the Accompaniment Brace Message

As mentioned briefly beforehand in the chapter, with PIM-DM, an interface stays pruned alone for

3 account by default. Clip letters account a accurate antecedent and accumulation (in added words, a particular

(S,G) SPT). Whenever a router receives a Clip message, it finds the analogous (S,G) SPT entry

and marks the interface on which the Clip bulletin was accustomed as “pruned.” However, it also

sets a Clip timer, absence 3 minutes, so that afterwards 3 minutes, the interface is placed into a forwarding

state again.

So, what happens with PIM-DM and pruned links? Well, the all-important links are pruned,

and 3 account afterwards they are added back. Added multicasts flow, and the links are pruned. Then

they are added back. And so on. So, aback Cisco created PIM V2 (published as experimental

RFC 3973), it included a affection alleged accompaniment refresh. Accompaniment Brace letters can anticipate this

rather inefficient behavior in PIM-DM adaptation 1 of pruning and automatically unpruning

interfaces.

Figure 17-9 shows an archetype that begins with the aforementioned accompaniment as the arrangement declared at the end

of the above-mentioned section, “Rules for Pruning,” area the articulation amid R1 and R2 and the link

between R2 and R3 accept been pruned. Almost 3 account accept passed, and the links are about to

be added to the SPT afresh due to the cessation of the Clip timers.

Example 17-6 Multicast Avenue Table Access for the Accumulation 226.1.1.1 for R1

(10.1.1.10/32, 226.1.1.1), 00:08:35/00:02:42, flags: CT

Incoming interface: FastEthernet0/0, RPF nbr 0.0.0.0

Outgoing interface list:

Serial0/0, Prune/Dense, 00:00:12/00:02:48

602 Affiliate 17: IP Multicast Routing

Figure 17-9 How PIM-DM Adaptation 2 Uses Accompaniment Brace Messages

The PM Accompaniment Brace bulletin can be sent, aloof afore a neighbor’s Clip timer expires, to keep

the interface in a pruned state. In Figure 17-9, the afterward accomplish do aloof that:

1. R3 monitors the time aback it beatific the aftermost Clip to R2. Aloof afore the Clip timer expires,

R3 decides to accelerate a Accompaniment Brace bulletin to R2.

2. R3 sends the Accompaniment Brace bulletin to R2, referencing SPT (10.1.1.10, 226.1.1.1).

3. R2 reacts by resetting its Clip timer for the interface on which it accustomed the Accompaniment Refresh

message.

4. Because R2 had additionally pruned itself by sending a Clip bulletin to R1, R2 additionally uses State

Refresh letters to acquaint R1 to leave its s0/0 interface in a pruned state.

As continued as R3 keeps sending a Accompaniment Brace bulletin afore the Clip timer on the upstream

router (R2) expires, the SPT will abide stable, and there will not be the alternate times of flooding

of added multicasts for that (S,G) tree.

Graft Message

When new hosts accompany a group, routers may charge to change the accepted SPT for a accurate (S,G)

entry. With PIM-DM, one advantage could be to delay on the pruned links to expire. For example, in

Figure 17-9, R3 could artlessly abdicate sending Accompaniment Brace messages, and aural 3 account at most,

Fa0/0

10.1.1.0/24

10.1.2.0/24

10.1.5.0/24

10.1.6.0/24

10.1.3.0/24

S0/0 S0/0 .2

S0/1

S0/0

R1 R2

.1 .2

.10

Destination Address: 226.1.1.1

Source Address: 10.1.1.10

I got a accompaniment refresh

message – displace my

prune timer on S0/1!

My Clip timer for (10.1.1.10,

226.1.1.1), interface S0/0, is

about to expire. Accelerate a staterefresh

message!

State

Refresh

State

Refresh

Multicast Traffic

Dense-Mode Acquisition Protocols 603

R3 would be accepting the multicast packets for some (S,G) SPT again. However, cat-and-mouse on the

(default) 3-minute Clip timer to expire is not actual efficient. To acquiesce routers to “unprune” a

previously pruned interface from an SPT, PIM-DM includes the Affix message, which is defined

as follows:

A router sends a Affix bulletin to an upstream neighbor—a acquaintance to which it had

formerly beatific a Clip message—causing the upstream router to put the articulation aback into a

forwarding accompaniment (for a accurate (S,G) SPT).

Figure 17-10 shows an archetype that uses the aforementioned advancing archetype network. The action shown

in Figure 17-10 begins in the aforementioned accompaniment as declared at the end of the above-mentioned section, “Steady-

State Operation and the Accompaniment Brace Message.” Neither host H1 nor H2 has abutting group

226.1.1.1, and R2 and R3 accept been absolutely pruned from the (10.1.1.10, 226.1.1.1) SPT. Referring

to Figure 17-10, R1’s s0/0 interface has been pruned from the (S,G) SPT, so R2 and R3 are not

receiving the multicasts beatific by server S1 to 226.1.1.1. The archetype afresh begins with host H2

joining accumulation 226.1.1.1 again.

Figure 17-10 R3 and R2 Accelerate Affix Messages

Without the Affix message, host H2 would accept to delay for as abundant as 3 account afore it would

receive the accumulation traffic. However, with the afterward steps, as listed in Figure 17-10, H2 will

receive the packets in aloof a few seconds:

1. Host H2 sends an IGMP Accompany message.

Fa0/0

10.1.1.0/24

10.1.2.0/24

10.1.5.0/24

10.1.6.0/24

10.1.3.0/24

S0/0 S0/0 .2

S0/1

S0/0

R1 R2

.1 .2

.10

My (10.1.1.10, 226.1.1.1)

entry lists S0/0 and 10.1.3.2

as my RPF interface and

neighbor – accelerate a Affix there!

Graft

My (10.1.1.10, 226.1.1.1)

entry lists S0/0 and 10.1.2.1

as my RPF interface and

neighbor – accelerate a Affix there!

IGMP Join

for 226.1.1.1

2. R3 looks for the RPF interface for its (S, G) accompaniment advice for the accumulation 226.1.1.1 (see

earlier Archetype 17-5), which shows the admission interface as s0/0 and RPF acquaintance as

10.1.3.2 for the group.

3. R3 sends the Affix bulletin out s0/0 to R2.

4. R2 now knows it needs to be accepting letters from 10.1.1.10, beatific to 226.1.1.1. However,

R2’s (S,G) access additionally shows a P flag, acceptation R2 has pruned itself from the SPT. So, R2 finds

its RPF interface and RPF acquaintance IP abode in its (S,G) entry, which references interface

s0/0 and router R1.

5. R2 sends a affix to R1.

At this point, R1 anon puts its s0/0 aback into the approachable interface list, as does R2, and now

H2 receives the multicast packets. Note that R1 additionally sends a Affix Ack bulletin to R2 in response

to the Affix message, and R2 sends a Affix Ack in acknowledgment to R3’s Affix bulletin as well.