CCNP Tutorial For The BSCI Exam:
Rendezvous Point Discovery Methods
Chris Bryant, CCIE #12933
Vital Reading And Watching For All Cisco Certification Candidates:
The July 2010 CCNP Changes (And How To Beat Them!)
In earlier installments of this CCNP tutorial series for the BSCI exam, we saw how both PIM Sparse Mode and PIM Dense Mode operate.
During the PIM Sparse discussion, we saw the role of the rendezvous point (RP). It's one thing to decide which router should be the RP, but it's another to make sure all the other routers know where the RP is! The available methods depend on the PIM version in use.
PIM Version 1: Static configuration or Auto-RP
PIM Version 2: Static configuration, Auto-RP, or bootstrapping, the open standard method.
Let's take a closer look at these methods using the following hub-and-spoke network, beginning with the static configuration method. All routers are using their Serial0 interfaces on the 172.12.123.0 /24 network, with their router number as the fourth octet.
Each router will have multicast routing enabled with the ip multicast-routing command. Under the assumption that we will not have many recipients, we'll configure these routers for sparse mode. (If we had many recipients, we'd use dense mode.) All three routers will have R1 configured as the RP.
R1(config)#ip multicast-routing
R1(config)#ip pim rp-address 172.12.123.1
R1(config)#int s0
R1(config-if)#ip pim sparse
R2(config)#ip multicast-routing
R2(config)#ip pim rp-address 172.12.123.1
R2(config)#int s0
R2(config-if)#ip pim sparse
R3(config)#ip multicast-routing
R3(config)#ip pim rp-address 172.12.123.1
R3(config)#int s0
R3(config-if)#ip pim sparse
The command show ip pim neighbor verifies that PIM is running and in Version 2 on all interfaces.
R1#show ip pim neighbor
PIM Neighbor Table
Neighbor Address Interface Uptime Expires Ver Mode
172.12.123.3 Serial0 00:11:08 00:01:37 v2 (DR)
172.12.123.2 Serial0 00:11:37 00:01:38 v2
Both R2 and R3 show R1 as the RP for the multicast group 224.0.1.40, which is the RP-Discovery multicast group.
R2#show ip pim rp
Group: 224.0.1.40, RP: 172.12.123.1, v1, uptime 00:12:51, expires 00:03:11
R3#show ip pim rp
Group: 224.0.1.40, RP: 172.12.123.1, v1, uptime 00:12:43, expires 00:04:20
You don't have to use the same router as the RP for every single multicasting group. An access-list can be written to name the specific groups that a router should serve as the RP for.
We'll take a look at that configuration after this brief yet important note - and I look forward to continuing to help you earn your CCNP!
Earn Your CCNP With The Personal Guarantee Of Chris Bryant, CCIE #12933:
“I GUARANTEE You'll Pass The Current CCNP Exams - BSCI, ONT, ISCW, and BCMSN - Before The July 31, 2010 Cutoff Date With My CCNP Study Packages ...
... And If You Don't Pass FOR ANY REASON Before That Time, I'll Give You a 100% Free CCNP Study Package Download For The New Exam Track!"
You Also Get A FREE CCNA Security Study Package With The Purchase Of Any CCNP Study Package!
 
An access-list can be written to name the specific groups that a router should serve as the RP for, and that access-list can be called in the ip pim rp-address command. I'll show you the config for R1, and it would be the same on both R2 and R3.
R1(config)#access-list 14 permit 224.0.1.40
R1(config)#ip pim rp-address 172.12.123.1 ?
<1-99> Access-list reference for group
<1300-1999> Access-list reference for group (expanded range)
WORD IP Named Standard Access list
override Overrides Auto RP messages
<cr>
R1(config)#ip pim rp-address 172.12.123.1 14
There's one more option in the ip pim rp-address command you should note. See the override option in the above IOS Help readout? Using that option will allow this static RP configuration to override any announcement made by Auto-RP, Cisco's proprietary method of announcing RPs to multicast routers running Sparse Mode. (Auto-RP is now supported by some non-Cisco vendors.)
And how do you configure Auto-RP? Glad you asked!
Configuring Auto-RP
Auto-RP will have one router acting as the mapping agent (MA), and it is the job of this router to listen to the multicast address 224.0.1.39.
It's with this address that routers announce themselves as candidate RPs (C-RP). The MA listens to the candidate announcements, and then decides on a RP for each multicast group. The MA then announces these RPs on 224.0.1.40 via RP-Announce messages.
We'll first configure R2 and R3 as candidate RPs. PIM Sparse is already running on all three routers' serial interfaces and multicasting has been enabled on all three routers as well.
R2(config)#ip pim send-rp-announce ?
BRI ISDN Basic Rate Interface
Ethernet IEEE 802.3
Null Null interface
Serial Serial
R2(config)#ip pim send-rp-announce serial0 ?
scope RP announcement scope
R2(config)#ip pim send-rp-announce serial0 scope 5
R3(config)#ip pim send-rp-announce serial0 scope 5
The scope value sets the TTL of the RP-Announce messages.
Now that the candidate RPs are configured, R1 will be configured as the mapping agent.
R1(config)#ip pim send-rp-discovery serial 0 scope 5
As multicast groups are added to the network, both R2 and R3 will contend to be the RP by sending their RP-Announce messages on 224.0.1.39.
As the mapping agent, R1 will decide which router is the RP, and will make that known via RP-Discovery messages sent on 224.0.1.40.
We have one more RP discovery method to discuss, and we'll do just that on Monday, March 29 on our BSCI Exam Resource Page.
Visit every day in March and April for new CCNP study material - and watch the Bulldog Blog, too! Earn Your CCNP With The Personal Guarantee Of Chris Bryant, CCIE #12933:
“I GUARANTEE You'll Pass The Current CCNP Exams - BSCI, ONT, ISCW, and BCMSN - Before The July 31, 2010 Cutoff Date With My CCNP Study Packages ...
... And If You Don't Pass FOR ANY REASON Before That Time, I'll Give You a 100% Free CCNP Study Package Download For The New Exam Track!"
You Also Get A FREE CCNA Security Study Package With The Purchase Of Any CCNP Study Package!
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