Planning for Multicast Services in a Network
So what’s bare to arrange IP multicast? A lot of backbone and planning is needed. OK, so
maybe backbone and planning aren’t the alone things needed, but they help. All accessories in the
network should be able to adapt multicasts. What accessories are important? How about routers,
switches, and servers, for starters. All your audience accepting multicasts ability be helpful. The
point actuality is that the adjustment interface cards (NICs) should abutment multicasts.
The use of switches is about a claim for today’s high-speed, high-bandwidth LAN
environment. However, not all switches are up to the assignment of assuming able multicasting.
The about-face backplane or switching bolt charge acquiesce a aerial allotment of multicast cartage to
be passed. So, back arcade for a about-face architecture, be acquainted of the charge for a robust
switching fabric. The Catalyst about-face architectonics is advised for able multicasting.
In action campus networks, the use of Layer 2 switches is not the end solution. A Layer 3
routing device, such as a router about-face bore or a abounding absolute alien router, is additionally needed.
Figure 11-2 illustrates the adjustment accessories about bare to abutment a adjustment with multicast
services.
Figure 11-2 IP Multicast Components
Cisco acquisition accessories accommodate abutment for multicasts through the use of multicast routing
protocols such as Distance Vector Multicast Acquisition Agreement (DVMRP), Agreement Independent
Multicast (PIM), and Core-Based Copse (CBT), as discussed in detail in Affiliate 10.
Configuring IP Multicast
IP multicast and the assignment configuring it are somewhat avant-garde topics. Fortunately, the material
on the CCNP Switching assay covers alone the basics of configuring IP multicast. We will do
the aforementioned here, but will account as alternative a few of the avant-garde tasks.
Core
Video
servers
Router
Distribution
switch Access
switch
Host
374 Affiliate 11: Configuring Multicast Networks
The two basal tasks in enabling multicast are
• Enabling IP multicast routing
• Enabling PIM on an interface
Advanced tasks are alternative and accommodate the following:
• Configuring a affair point
• Configuring the Time To Live (TTL) threshold
• Debugging IP Multicast
• Configuring Internet Accumulation Management Agreement (IGMP)
• Enabling Cisco Accumulation Management Agreement (CGMP)
Enabling IP Multicast Routing
Enabling IP multicast acquisition allows the Cisco IOS software to advanced multicast packets.
Much like enabling added acquisition protocols, you charge accomplish an admission in all-around configuration
mode to about-face this on for the absolute router. Then, application interface commands, you can about-face on
various modes of multicast acquisition application alone specific interfaces. To accredit IP multicast routing
on the router, admission the afterward command in all-around agreement mode.
Router(config)#ip multicast-routing
To attenuate IP multicast routing, admission the no ip multicast-routing command. By default,
multicast acquisition is disabled on an interface.
Enabling PIM on an Interface
When you accredit multicast acquisition on a avenue processor or router, it is candy on an
individual interface basis. Enabling anniversary alone interface acclimated with a specific multicast
routing agreement is necessary.
The command to accredit PIM on an interface is
DallasR1>(config-if)#ip pim {dense-mode | sparse-mode | sparse-dense-mode}
The options for this command are authentic as follows.
• dense-mode—Enables abutting approach of operation. Abutting approach is acclimated back all routers in
the adjustment will charge to administer multicast cartage for anniversary multicast group.
• sparse-mode—Enables dispersed approach of operation. Dispersed approach is acclimated back relatively
few routers in the adjustment will be complex in anniversary multicast.
Configuring IP Multicast 375
• sparse-dense-mode—The interface is advised in the approach in which the accumulation operates. If
the accumulation is operating in dispersed mode, the interface does as well. If the accumulation is operating
in abutting mode, afresh the interface does.
PIM can be implemented in three altered modes: dispersed mode, abutting mode, or a combination
called sparse-dense mode, as defined by the ip pim options ahead listed. The approach used
depends on the “density” of the hosts in an area.
Enabling PIM in Abutting Mode
In abutting mode, the antecedent of the multicast and its receivers are all in abutting proximity, such as a
campus environment. Abutting approach should be acclimated back bandwidth is plentiful, due to periodic
flooding. Pruning is acclimated in this ambiance to abstain accidental multicast packets being
flooded to a router with no anon affiliated neighbors.
Outgoing interface lists (oilist) are acclimated to affectation those interfaces that accommodated one of the
following criteria:
• An interface is heard from a PIM neighbor.
• A host has abutting a accumulation that uses that interface.
• A accurate interface has been manually configured to accompany a group.
Enabling PIM in Dispersed Mode
Sparse approach should be configured back there are few multicast hosts, appropriately the appellation sparse
mode. Because they are sparse, a affair point is bare in this scheme.
Sparse approach protocols are added adapted for ample internetworks area abutting mode
protocols would decay bandwidth by calamity packets to all genitalia in the adjustment and afresh prune
back all exceptionable connections. Dispersed approach protocols use absolute accompany letters to set up
distribution trees. Timberline accompaniment is afresh set up alone on routers on the administration tree, and data
packets are alone forwarded to LANs that accept hosts who accompany the group. Abutting approach protocols
build alone source-distribution trees—they actuate the area of receivers by calamity data
throughout the adjustment and afresh pruning off the receiverless branches. PIM dispersed approach can
be acclimated for any aggregate of sources and receivers, whether densely or sparsely populated.
Rendezvous credibility (RPs) are configured and act as a array of proxy for multicast hosts. Multicast
senders use the RP to advertise the hosts, and multicast receivers use RP to apprentice about other
hosts.
376 Affiliate 11: Configuring Multicast Networks
Enabling PIM in Sparse-Dense Mode
To configure PIM sparse-dense mode, use the afterward commands on all PIM routers inside
the PIM domain, alpha in all-around agreement mode:
Router#ip multicast-routing
Router#interface blazon number
Router#ip pim sparse-dense-mode
Verifying PIM Configuration
You can verify the PIM agreement that you aloof completed by accounting the following
command:
DallasR1>#show ip pim interface [type number] [count]
where blazon is the interface blazon and the cardinal is the cardinal of the interface. The count
parameter represents the cardinal of packets accustomed and beatific out the interface.
Selecting a Appointed Router
In a accustomed activity multicast network, PIM queries are beatific periodically to ascertain other
routers in the adjustment alive PIM. For multi-access networks such as Ethernet, PIM queries
are beatific to the acclaimed multicast abode of 224.0.0.2, contrarily accepted as “all routers.” In
a multi-access network, a appointed router is elected. If this action sounds accustomed to you,
you ability bethink it as a action additionally acclimated in OSPF networks.
The acclamation action is additionally actual agnate to OSPF, which uses the accomplished IP abode received
in PIM concern letters from a adjustment device’s neighbors. If no PIM queries are accustomed after
a accustomed time period, the acclamation action for Appointed Router runs again.
When alive PIM in dispersed mode, the appointed router is amenable for sending multicast
join letters to the RP on account of host computers on the network. No appointed router exists
when alive PIM in abutting mode.
Displaying PIM Neighbors
As is archetypal on a Cisco router, a appearance command will affectation PIM neighbors:
DallasR1>#show ip pim acquaintance blazon number
where blazon is the blazon of interface and cardinal is the cardinal of the interface. On a Avenue Switch
Module, the blazon would be a accurate VLAN and the cardinal a accurate VLAN number
(VLAN 10 is an example). Archetype 11-1 shows some archetypal achievement from the appearance ip pim
neighbor command.
Configuring IP Multicast 377
Most of the advice in Archetype 11-1 is self-explanatory. The Expires constant is defined
as the breadth of time that the PIM acquaintance is advised active. Note that the appointed router
is apparent out to the appropriate as (DR).
Configuring a Affair Point
One of the appearance that you accept to configure if you use PIM in dispersed approach is a Rendezvous
Point (RP).
The routers apprentice that they are RPs automatically. RPs are acclimated by multicast senders in a sparse
mode ambiance to advertise their existence. Through the destination, receivers apprentice about
new senders.
Multi-RP environments can be configured for any accustomed multicast group. One appellation acclimated in the
description of RPs is blade routers. Blade routers are either anon affiliated to a multicast group
member or to a sender.
The RP abode is acclimated by first-hop routers to accelerate PIM annals letters on account of a host
sending a packet to the group. The RP abode is additionally acclimated by last-hop routers to accelerate PIM join/
prune letters to the RP to acquaint about accumulation membership. The RP abode is configured
only on the first-hop and last-hop routers (leaf routers).
A PIM router can be configured as an RP for added than one group. A accumulation can additionally accept more
than one RP configured. An admission account is acclimated to actuate the groups for which the router is
an RP.
Although a accumulation can accept added than one RP, alone one RP abode is acclimated per accumulation at any
given time. You can configure assorted bombastic RPs, but alone one is used.
To configure the abode of the RP, use the afterward command in all-around agreement mode:
DallasR1>#ip pim rp-address ip-address [group-access-list-number][override]
As usual, you can attenuate the RP abode by application the no anatomy of the command.
Example 11-1 appearance ip pim acquaintance Command Achievement Displays Advice About PIM Neighbors
DallasR1>show ip pim neighbor
PIM Acquaintance Table
Neighbor Abode Interface Uptime Expires Mode
192.168.100.1 FastEthernet0 1w2d 00:01:33 Dense
192.168.101.1 FastEthernet0 1w4d 00:01:21 Abutting (DR)
192.168.21.1 FastEthernet0 1w1d 00:01:16 Dense
192.168.57.1 FastEthernet0 2w5d 00:01:33 Dense
192.168.99.1 Serial0.4 22:00:01 00:01:08 Dense
192.168.78.1 Serial0.1 22:00:15 00:01:19 Dense
378 Affiliate 11: Configuring Multicast Networks
Auto-RP
Auto-RP is a affection that automates the administration of group-to-RP mappings in a PIM
network. This affection has the afterward benefits:
• Easy-to-use assorted RPs aural a adjustment to serve altered accumulation ranges.
• Allows amount agreeable amid altered RPs and adjustment of RPs according to the
location of accumulation participants.
• Avoids inconsistent, chiral RP configurations that can account connectivity problems.
Multiple RPs can be acclimated to serve altered accumulation ranges or serve as hot backups of anniversary other.
To accomplish Auto-RP work, you charge baptize a router as an RP Mapping Abettor that receives the
RP-announcement letters from the RPs and arbitrates conflicts. The RP mapping abettor then
sends the constant group-to-RP mappings to all added routers. Thus, all routers automatically
discover which RP to use for the groups they support.
One way to alpha is to abode (preserve) the absence RP for all all-around groups at or abreast the border
router of your acquisition domain, while agreement addition RP in a added centrally amid router for
all bounded groups application the administratively scoped addresses (239.x.x.x).
As illustrated by Figure 11-3, Router X announces to the Mapping Abettor that it would like to
be the RP for Accumulation X and Router Y announces to the Mapping Abettor that it would like to be
the RP for Accumulation Y. The Mapping Abettor afresh passes this advice to the Appointed Routers
(DR).
NOTE If you configure PIM in dispersed approach or sparse-dense approach and do not configure Auto-RP, you
must statically configure an RP as declared in the area “Configuring a Affair Point”
later in this chapter.
If you are ambience up Auto-RP in a new internetwork, you do not charge a absence RP. For the initial
deployment of Auto-RP into an absolute dispersed approach cloud, use the afterward guidelines to
allow basal disruption to the absolute multicast infrastructure:
Step 1 Accept a absence RP.
Step 2 Advertise the RP and the accumulation ambit it serves.
Step 3 Accredit the RP mapping agent.
Step 4 Verify the group-to-RP mapping.
Configuring IP Multicast 379
Figure 11-3 Affair Point Announcement
Follow the aforementioned accomplish to set up Auto-RP in a new internetwork, but omit Step 1 (default RPs
are not appropriate in a new internetwork). The sections that chase call anniversary of these accomplish in
further detail.
Step 1: Accept a Absence RP
Sparse approach environments charge a absence RP; sparse-dense approach environments do not. If you
have sparse-dense approach configured everywhere, you do not charge to accept a absence RP.
Adding Auto-RP to a dispersed approach billow requires a absence RP. In an absolute PIM dispersed mode
region, you charge ascertain at atomic one RP beyond the adjustment that has acceptable connectivity and
availability. By “existing PIM additional approach region,” we beggarly that the ip pim rp-address
command is already configured on all routers in this network.
Use that RP for the all-around groups (for example, 224.x.x.x and added all-around groups). You do
not charge to reconfigure the accumulation abode ambit that RP serves. RPs apparent dynamically
through Auto-RP booty antecedence over statically configured RPs. Application a additional RP for the
local groups is desirable.
RP Mapping Agent
Router X
Router Y
DR DR
380 Affiliate 11: Configuring Multicast Networks
Step 2: Advertise the RP and the Accumulation Ambit It Serves
Find addition router to serve as the RP for the bounded groups. The RP mapping abettor can double
as an RP itself. Accredit the accomplished ambit of 239.x.x.x to that RP or accredit a subrange of that (for
example, 239.2.x.x).
To baptize that a router is the RP, accomplish the afterward assignment in all-around agreement mode:
DallasR1>#ip pim send-rp-announce blazon cardinal ambit ttl group-list access-listnumber
To change the accumulation ranges this RP optimally serves in the future, change the announcement
setting on the RP. If the change is valid, all added routers automatically accept the new group-to-
RP mapping.
The afterward archetype advertises the IP abode of Ethernet 0 as the RP for the administratively
scoped groups.
Step 3: Accredit the RP Mapping Agent
The RP mapping abettor is the router that sends the accurate Discovery packets cogent other
routers which group-to-RP mapping to use. Such a role is all-important in the accident of conflicts
(such as overlapping group-to-RP ranges).
Find a router whose connectivity is not acceptable to be disconnected and accredit it the role of RP
mapping agent. All routers aural TTL cardinal of hops from the antecedent router accept the Auto-
RP Discovery messages. To accredit the role of RP mapping abettor in that router, admission the
following command in all-around agreement mode:
DallasR1>#ip pim send-rp-discovery ambit ttl
Step 4: Verify the Group-to-RP Mapping
To see if the group-to-RP mapping has arrived, affair one of the afterward commands in EXEC
mode on the appointed routers:
DallasR1>#show ip pim rp mapping
DallasR1>#show ip pim rp [group-name | group-address] [mapping]
The aboriginal command is a all-encompassing appearance all mapping, but the additional one allows you to specify
either the alone accumulation or accumulation address.