Multicast – All you need to know for the CCIE R&S lab


Hello !

We all know how much information is on the internet about multicast and believe me my intension is not to create another post about multicast just so it’s there and is not different from what you can find on the internet but to show you that there is not really that much to it when it comes to CCIE R&S exam. Of course there are hundreds of books written about Multicast but for CCIE R&S it’s easy !multicast

Multicast has always been one of those sections in networking that I find it really hard to understand logically and from my experience and people I have talked to about it over the years almost 90% of them have had the same view !

Recently I decided to face it and once for all understand what is going on in Multicast. I have watched and read tons of multicast materials in order to prepare myself for the CCIE R&S exam and believe it or not in every single book and every single video course I’d see exact same features just explained differently ….

Well I’ve decided to put it all together and show you how much you actually need to know to pass this section on the exam and it’s not a lot !

Set up a practise LAB and experiment using all below commands then do it all over again until you feel confident , retain that knowledge and that’s it !multicast

Multicast scope : 224.0.0.0 – 239.0.0.0 /4
Enabel PIM under interface level
(config-if)ip pim dense-mode
(config-if)ip pim sparse-mode
(config-if)ip pim sparse-dense-mode

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THREE METHODS OF SPECIFYING RP

 Static assignemnt
 Auto RP (Cisco only)
 Bootstrap Router (BSR-IETF) known as a mapping agent – industry standard RP

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STATIC RP
ACL REFERENCES FOR WHICH MULTICAST GROUPSdense-mode-1
ALL ROUTERS POINT TO RP

Static RP for all groups
ip pim rp-address 200.0.0.4

Static RP for specific groups
access-list 10 permit 228.0.0.0 1.255.255.255
ip pim rp-address 200.0.0.4 10

Static RP – force a particular RP for one group but use auto methods for others
access-list 10 permit 228.0.0.0 1.255.255.255
ip pim rp-address 200.0.0.4 10 override

In our case the groups are 228.0.0.0 and 229.0.0.0

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AUTO RP
224.0.1.40 – All other routers will be listening for messages on the mapping agent on 224.0.0.40
224.0.1.39 – RPs send their information to 224.0.0.39 which is the mapping agent

AUTO RP for all groups
Scope tells the router how far multicast packect can traverse the network – hop count
ip pim send-rp-announce Loopback0 scope 15

AUTO RP for specific groups
access-list 10 permit 228.0.0.0 1.255.255.255
ip pim send-rp-announce Loopback0 scope 15 group-list 10

AUTO RP for specific groups with interval change
access-list 10 permit 228.0.0.0 1.255.255.255
ip pim send-rp-announce loopback 0 sco 15 group-list 10 interval 10

Updates will now be sent every 10 seconds. The default is 60 seconds.

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dense-mode-1-sparseAUTO RP LISTENER

If only SPARSE MODE is configured throughout the network remember that for AUTO RP DENSE MODE is necessary to move multicast traffic.
In this case either configure IP PIM SPARSE-DENSE-MODE under each interface on every device and you’re in a lab environment and you are not allowed
to do so then the global command you want is:

ip pim autorp listener

The IP Pim autorp listener allows the Group 224.0.0.39 & 224.0.0.40 to be densed flooded

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MA – MAPPING AGENT
BEST PLACE IS ON HUB ROUTER
YOU CAN HAVE MORE THAN ONE MA ON THE NETWORK – HIGHEST IP ADDRESS OF MA WINS

Configures MA for all RPs and all multicast groups
ip pim send-rp-discovery Loopback0 scope 15

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FILTERING

To ensure that only R4 is accepted as RP for only 228.0.0.0 & 229.0.0.0 groups

IP access-list standard R4
    10 permit 200.0.0.4
IP access-list standard R4GROUP
    10 permit 228.0.0.0 1.255.255.255

ip pim rp-announce-filter rp-list R4 group-list R4GROUP

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BSR (bootstrap router)
USES 224.0.0.13 BUT HAS NOTHING TO DO WITH DENSE-MODE
SPARSE MODE ONLY !
YOU CAN HAVE MORE THAN ONE BSP-MA ON THE NETWORK – HIGHEST PRIORITY OR HIGHEST IP ADDRESS OF BSR-MA WINS

Configures BSR-MA
ip pim bsr-candidate loopback 0 24 200

The router will become the BSR with the hash 24 and priority 200
The hash (24 in our case) is used for load-balancing purposes between RPs

Configures BSR RP for all groups
ip pim rp-candidate loopback 0

Configures BSR RP for specific groups
access-list 10 permit 232.0.0.0 7.255.255.255
ip pim rp-candidate loopback 0 group-list 10

Configures BSR RP for specific groups with interval change
access-list 10 permit 232.0.0.0 7.255.255.255
ip pim rp-candidate loopback 0 group-list 10 interval 10

Configures BSR RP for specific groups with interval change and priority
access-list 10 permit 232.0.0.0 7.255.255.255
ip pim rp-candidate loopback 0 group-list 10 interval 10 priority 200

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PIM BORDERS
FOR SEPERATE MULTICAST DOMAIN WHERE PIM AND BSR SHOULD NOT MIX
IN THE EXAM GOOD PLACE TO PUT THIS COMMAND (unless otherwise specified) WOULD BE ON EACH ROUTER INTERFACE THAT CONNECTS TO BACKBONE ROUTER

(config-if)ip pim bsr-border

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MULTICAST BOUNDARY
DEFINE WHICH MULTICAST TRAFFIC CAN PASS THROUGH

Access-list 13 deny 239.0.0.0. 0.255.255.255
Access-list 13 permit 224.0.0.0 15.255.255.255

(config-if)ip multicast boundary 13

This will permit groups 224.0.0.0 15.255.255.255 and deny 239.0.0.0. 0.255.255.255

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MULTICAST FRAME RELAY
DOES NOT WORK WITH DENSE MODE
Intended to overcome the default split-horizon policy that prevents forwarding packets out the same interface they were received on. This is a loop prevention method.
ip pim nbma-mode operates like OSPF’s point-to-multipoint mode, where the connection from the HUB to each SPOKE is treated like a separate point-to-point link, and separate mroute entries are created in the HUB’s multicast routing table.
There is no reason to configure this mode on a SPOKE router – the SPOKE router only has a single connection to the HUB router, and no direct connections to any other router in the hub and spoke environment

On HUB Router interface
(config-if)ip pim nbma-mode
(config-if)ip pim sparse-mode

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DVMRP – DISTANCE VECTOR MULTICAST ROUTING PROTOCOL
USED TO CONNECT MULTICAST NETWORK ACCROSS A NON-MULTICAST NETWORKS

R2
interface Tunnel0
 ip address 10.24.24.2 255.255.255.0
 ip pim sparse-dense-mode
 tunnel source 150.100.24.2
 tunnel destination 150.100.24.4
 tunnel mode dvmrp

R4
interface Tunnel0
 ip address 10.24.24.4 255.255.255.0
 ip pim sparse-dense-mode
 tunnel source 150.100.24.4
 tunnel destination 150.100.24.2
 tunnel mode dvmrp

If you receive below messages when doing debugs
RPF lookup failed for source / not RPF interface

USE STATIC MROUTE TO FIX
ip mroute 0.0.0.0 0.0.0.0 tunnel 0

This will send any multicast groups via Tunnel0 interface

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JOINING MULTICAST GROUPS

ip igmp join-group 228.0.0.0
(process switched traffic)

ip igmp static-group 228.0.0.0
(fast switched traffic)

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PIM DR PRIORITY
Every multi-access interface with multiplie PIM devices elects a PIM DR
Default priority is 1
Highest IP address wins

(config-if)#ip pim dr-priority 100

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MULTIPATH MULTICAST
Allows load-sharing for multicast over equal cost paths

ip multicast multipath

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MSDP – MULTICAST SOURCE DISCOVERY PROTOCOL
MULTICAST ANYCAST
When we have a shared ip address on our network RP’s must be able to somehow sync with eachother
as otherwise all other routers will lose multicast connectivity if one of the RP’s goes down
Runs over TCP session between RPs (TCP/639)

R1
int loo 0
ip add 17.17.17.17 255.255.255.255
ip pim sparse-mode
ip pim send-rp-announce loo0 scope 15
ip msdp peer 17.17.17.17 connect-source loopback 0
R7
int loo 0
ip add 17.17.17.17 255.255.255.255
ip pim sparse-mode
ip pim send-rp-announce loo0 scope 15
ip msdp peer 17.17.17.17 connect-source loopback 0

17.17.17.17 must be reachable across the network

 

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MULTICAST BIODIRECTIONAL PIM – Bidir
PHANTOM RPs
ALLOWS MULTICAST TO SCALE WITH AN ARBITRARY NUMBER OF SOURCES AND RECEIVERS WITHIN MULTICAST DOMAIN

On all routers :
ip pim bidir-enable
ip pim rp-address 22.22.22.2 override bidir
ip pim rp-candidate 22.22.22.2 override bidir
ip pim send-rp-announce 22.22.22.2 override bidir

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Tip : wr t is a short for show run

Please let me know if I’ve missed anything

Enjoy !

Tom

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