MPLS Multicast Routing (IOS)
Here are my notes for configuring multicast in an MPLS
environment from a recent training. This will be broken down into four
major sections with output samples for each configuration step and validation:
- MPLS in the Core
- Multicast between the PE/CE
- Multicast Distribution Tree
- Final Validations and Test
BASIC TOPOLOGY
MPLS IN THE CORE
Core Network Setup Steps
The assumption is that you already have a fully configured and
functioning IGP. These configuration steps are performed on the 'P'
routers within the core of the MPLS network.
- Enable multicast routing
- Configure PIM on the Interface
- If using sparse-mode, configure rendezvous point in the core
1. Enable Multicast routing
ip
multicast-routing
2. Configure PIM on the Interface
interface x/y
ip pim
sparse-mode
The easiest way to avoid trouble with the RPF check and
multicast forwarding is to maintain a 1:1 ratio between your PIM enabled
interfaces and your IGP enabled interfaces.
3. Configure the rendezvous point
The configuration of the RP can be auto-rp, bootstrap router or
static. I chose bsr in this case.
ip pim bsr-candidate loopback0
ip pim
rp-candidate loopback0
Core Network Validation Steps
- Validate the appropriate interfaces are configured with PIM
- Validate the PIM neighbors are seen successfully
- Validate the RP is seen on all multicast enabled core routers
- Enable a multicast receiver in the core
- Compare the unicast routing table, rpf for the rp and the outgoing interfaces list
- Source multicast traffic to the receiver from another device
1. Validate PIM Interfaces
Compare the output of the 'show ip pim interface' command to your
diagram to ensure all required interfaces have been configured. Perform
this step on all routers in the MPLS core.
P5#sho ip pim int
Address Interface Ver/ Nbr Query DR
DR
Mode Count Intvl Prior
20.4.5.5 FastEthernet0/0 v2/S 1 30
1 20.4.5.5
20.5.6.5 FastEthernet0/1 v2/S 1 30
1 20.5.6.6
20.3.5.5 FastEthernet1/0 v2/S 0 30
1 0.0.0.0
20.5.19.5 FastEthernet1/1 v2/S 1 30
1 20.5.19.19
5.5.5.5 Loopback0 v2/S 0 30 1
5.5.5.5
2. Validate PIM Neighbors
Perform this test on all multicast enabled routers and validate
all interfaces are appropriately configured. In the sample topology all
interfaces have been PIM enabled.
show ip pim neighbor
SAMPLE OUTPUT
P5#sho ip pim neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR -
Designated Router, N - Default DR Priority,
P - Proxy
Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires
Ver DR
Address Prio/Mode
20.4.5.4 FastEthernet0/0
00:25:59/00:01:35 v2 1 / S P G
20.5.6.6 FastEthernet0/1
00:39:45/00:01:44 v2 1 / DR S P G
20.5.19.19 FastEthernet1/1
00:38:53/00:01:15 v2 1 / DR S P G
3. Validate RP Assignment
Execute this check on all core routers that are going to be
multicast enabled.
show ip pim rp mapping
P5#show ip pim rp mapping
PIM Group-to-RP Mappings
Group(s) 224.0.0.0/4
RP 4.4.4.4 (?), v2
Info source: 4.4.4.4
(?), via bootstrap, priority 0, holdtime 150
Uptime: 00:37:23, expires: 00:01:46
4. Enable Multicast Receiver
interface Loopback0
ip address 6.6.6.6
255.255.255.255
ip router isis 1
ip pim sparse-mode
ip igmp join-group 224.1.1.1
5. Unicast routing, rpf check and OIL
Validate the unicast route to the RP address and the rpf are in
agreement
P5#sho ip route 4.4.4.4
Routing entry for 4.4.4.4/32
Known via "isis",
distance 115, metric 10, type level-2
Redistributing via isis 1
Last update from 20.4.5.4 on FastEthernet0/0,
01:05:42 ago
Routing Descriptor Blocks:
* 20.4.5.4, from 4.4.4.4,
01:05:42 ago, via FastEthernet0/0
Route metric
is 10, traffic share count is 1
P5#sho ip rpf 4.4.4.4
RPF information for ? (4.4.4.4)
RPF interface:
FastEthernet0/0
RPF neighbor: ? (20.4.5.4)
RPF route/mask: 4.4.4.4/32
RPF type: unicast (isis 1)
Doing distance-preferred
lookups across tables
RPF topology: ipv4 multicast
base, originated from ipv4 unicast base
P5#sho ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B -
Bidir Group, s - SSM Group, C - Connected,
L -
Local, P - Pruned, R - RP-bit set, F - Register flag,
T -
SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
X -
Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD,
I - Received Source Specific Host Report,
Z -
Multicast Tunnel, z - MDT-data group sender,
Y -
Joined MDT-data group, y - Sending to MDT-data group,
V - RD
& Vector, v - Vector
Outgoing interface flags: H -
Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface,
Next-Hop or VCD, State/Mode
(*, 224.1.1.1), 01:04:13/00:03:20,
RP 4.4.4.4, flags: S
Incoming interface:
FastEthernet0/0, RPF nbr 20.4.5.4
Outgoing interface list:
FastEthernet0/1,
Forward/Sparse, 01:04:13/00:03:20
(*, 224.0.1.40), 01:20:58/00:02:16,
RP 0.0.0.0, flags: DCL
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 01:20:56/00:02:16
•
The incoming interface should match the RPF interfaces toward
the RP
•
The outgoing interface list (OIL) should contain the interface
toward the router with the igmp join statement
MULTICAST BETWEEN THE PE/CE
CE Router Configuration
The multicast configuration on the CE router will be the
standard type of enterprise multicast configuration. The same practice of
maintaining a 1:1 ratio of IGP enabled to multicast enabled interface parity
will help avoid RPF issues later.
- Enable Multicast Routing
- Enabled PIM on the interfaces
- Configure an rendezvous point for sparse mode multicast networks
Validate CE Multicast Configuration
- Validate PIM interfaces
- Validate PIM neighbors
- Validate RP within the local site with the RP (other sites won't see it until you configure the MDT piece)
** For brevity I have omitted the output of these commands as
the are the same as the previous and repeated again later.
PE to CE Configuration
- Enable multicast routing
- Enable multicast routing for the customer vrf
- Configure pim on the CE interface
1. Enable multicast routing
ip multicast-routing
2. Enable multicast routing on the customer VRF
ip multicast-routing vrf A
3. PIM on the CE
interface FastEthernet0/0
vrf forwarding A
ip address 10.1.2.2
255.255.255.0
ip pim sparse-mode
Validations
- Validate PIM interfaces in the VRF
- Validate the PIM neighbors in the VRF
- At the site where the RP exists, verify the PE sees the RP in the VRF
1. PIM Interfaces
PE1#show ip pim vrf A interface
Address Interface Ver/ Nbr Query DR DR
Mode Count Intvl Prior
10.1.2.2 FastEthernet0/0 v2/S 1 30 1 10.1.2.2
2. PIM Neighbors
PE1#sho ip pim vrf A neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR -
Designated Router, N - Default DR Priority,
P - Proxy
Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires
Ver DR
Address Prio/Mode
10.1.2.1 FastEthernet0/0 00:55:20/00:01:38 v2 1 / S P G
3. Validate the RP is seen on PE1 (connected to site with RP)
PE1#sho ip pim vrf A rp mapping
PIM Group-to-RP Mappings
Group(s) 224.0.0.0/4
RP 1.1.1.1 (?), v2
Info source: 1.1.1.1
(?), via bootstrap, priority 0, holdtime 150
Uptime: 01:29:19, expires: 00:01:56
MULTICAST DISTRIBUTION TREE
The MDT (multicast distribution tree) is the solution that
utilizes PIM in the core of the network (ASM, bidir, or SSM) and builds
multicast trees per VPN. The state information maintained in the core of
the network is limited to the information specifically required to maintain the
trees. The VRF default MDT configuration enables the automatic discover
of PE routers participating in the VPN (based on default mdt group) for ASM.
Customer (VPN) multicast traffic is encapsulated in provider multicast
groups.
This basic configuration example only shows the use of the
default mdt group. MDT data groups can be used to further optimize the
multicast traffic. ** See the reference links at the bottom for
additional info.
Configure MDT - Multicast Distribution Tree
- Enable MDT address family in BGP and activate ipv4 vpnv4 neighbors
- Configure the MDT address parameters in the vrf
- Ensure PIM is enabled on Loopbacks used for BGP neighbors
1. Enable the MDT address family in BGP
address-family ipv4 mdt
neighbor 19.19.19.19
activate
neighbor 19.19.19.19
send-community both
exit-address-family
2. Configure the MDT VRF default address
vrf definition A
rd 100:1
!
address-family ipv4
mdt default
239.255.255.255
route-target export 100:1
route-target import 100:1
route-target import 100:2
exit-address-family
!
3. Enable PIM on the loopbacks
interface
Loopback0
ip address 2.2.2.2
255.255.255.255
ip pim sparse-mode
end
Final Validation Steps
- Validate on PE the global s,g pairs for each PE
- Validate on PE the sho ip pim mdt
- Validate in core the s,g with shortest path tree flag
- Validate PEs see each other as neighbors within the vrf over tunnel
- Validate the non-RP customer sites now see the RP appropriately
- Configure a multicast receiver
- Source multicast traffic and review results
1. Global S,G pairs for PE routers
PE1#sho ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B -
Bidir Group, s - SSM Group, C - Connected,
L - Local,
P - Pruned, R - RP-bit set, F - Register flag,
T -
SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
X -
Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD,
I - Received Source Specific Host Report,
Z -
Multicast Tunnel, z - MDT-data group sender,
Y -
Joined MDT-data group, y - Sending to MDT-data group,
V - RD
& Vector, v - Vector
Outgoing interface flags: H -
Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface,
Next-Hop or VCD, State/Mode
(*, 239.255.255.255),
00:04:39/stopped, RP 4.4.4.4, flags: SJCFZ
Incoming interface:
FastEthernet1/0, RPF nbr 20.5.19.5
Outgoing interface list:
MVRF A,
Forward/Sparse, 00:04:37/00:01:22
(2.2.2.2, 239.255.255.255),
00:01:23/00:01:36, flags: JTZ
Incoming interface:
FastEthernet0/0, RPF nbr 20.6.19.6
Outgoing interface list:
MVRF A,
Forward/Sparse, 00:01:23/00:01:36
(19.19.19.19, 239.255.255.255),
00:04:39/00:03:00, flags: FT
Incoming interface:
Loopback0, RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet1/0,
Forward/Sparse, 00:02:28/00:02:50
(*, 224.0.1.40), 01:14:14/00:02:35,
RP 0.0.0.0, flags: DCL
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 01:14:12/00:02:35
2. Validate the MDT with 'show ip pim
mdt'
PE1#sho ip pim mdt
* implies mdt is the default
MDT
MDT Group/Num Interface
Source VRF
* 239.255.255.255 Tunnel2 Loopback0
A
PIM Neighbors
PE1#sho ip pim vrf A neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR -
Designated Router, N - Default DR Priority,
P - Proxy
Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires
Ver DR
Address Prio/Mode
10.1.2.1 FastEthernet0/0
00:18:11/00:01:35 v2 1 / S P G
19.19.19.19 Tunnel2 00:00:48/00:01:24
v2 1 / DR S P G
3. Validate the P routers in the core of the network
see the (S,G) mroute entries for the PE routers
P4#sho ip mroute
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B -
Bidir Group, s - SSM Group, C - Connected,
L -
Local, P - Pruned, R - RP-bit set, F - Register flag,
T -
SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
X -
Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD,
I - Received Source Specific Host Report,
Z -
Multicast Tunnel, z - MDT-data group sender,
Y -
Joined MDT-data group, y - Sending to MDT-data group,
V - RD
& Vector, v - Vector
Outgoing interface flags: H -
Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface,
Next-Hop or VCD, State/Mode
(*, 239.255.255.255),
00:53:11/00:03:22, RP 4.4.4.4, flags: S
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet1/1,
Forward/Sparse, 00:50:49/00:03:14
FastEthernet0/1,
Forward/Sparse, 00:53:11/00:03:22
(2.2.2.2, 239.255.255.255),
00:49:26/00:01:57, flags: PT
Incoming interface:
FastEthernet1/1, RPF nbr 20.2.4.2
Outgoing interface list:
Null
(19.19.19.19, 239.255.255.255),
00:52:09/00:03:00, flags: T
Incoming interface:
FastEthernet0/1, RPF nbr 20.4.5.5
Outgoing interface list:
FastEthernet1/1,
Forward/Sparse, 00:50:49/00:03:29
(*, 224.1.1.1), 01:57:34/00:03:04,
RP 4.4.4.4, flags: S
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/1,
Forward/Sparse, 01:57:34/00:03:04
(*, 224.0.1.40), 02:16:06/00:02:40,
RP 0.0.0.0, flags: DCL
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 02:16:04/00:02:24
4. Validate the PEs see each other as neighbors in the
customer VRF
PE1#sho ip pim vrf A
neighbor
PIM Neighbor Table
Mode: B - Bidir Capable, DR -
Designated Router, N - Default DR Priority,
P - Proxy
Capable, S - State Refresh Capable, G - GenID Capable
Neighbor Interface Uptime/Expires
Ver DR
Address Prio/Mode
10.1.2.1 FastEthernet0/0
01:01:10/00:01:34 v2 1 / S P G
19.19.19.19 Tunnel2
00:43:47/00:01:40 v2 1 / DR S P G
5. Validate RP Mapping at
non-RP sites
CE2#sho ip pim rp mapping
PIM Group-to-RP Mappings
Group(s) 224.0.0.0/4
RP 1.1.1.1 (?), v2
Info source: 1.1.1.1
(?), via bootstrap, priority 0, holdtime 150
Uptime: 00:52:27, expires: 00:01:37
6. Configure a multicast
receiver
The RP is located on CE1 so I will
join the 228.1.1.1 group on the CE3 router.
interface Loopback0
ip address 8.8.8.8 255.255.255.255
ip pim sparse-mode
ip igmp join-group 228.1.1.1
end
Mroute output from PE1:
We see the join from CE3 has traversed the MPLS core and the *,G
is seen on the PE router.
PE1#sho ip mroute vrf A
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, B -
Bidir Group, s - SSM Group, C - Connected,
L -
Local, P - Pruned, R - RP-bit set, F - Register flag,
T -
SPT-bit set, J - Join SPT, M - MSDP created entry, E - Extranet,
X -
Proxy Join Timer Running, A - Candidate for MSDP Advertisement,
U - URD,
I - Received Source Specific Host Report,
Z -
Multicast Tunnel, z - MDT-data group sender,
Y -
Joined MDT-data group, y - Sending to MDT-data group,
V - RD
& Vector, v - Vector
Outgoing interface flags: H -
Hardware switched, A - Assert winner
Timers: Uptime/Expires
Interface state: Interface,
Next-Hop or VCD, State/Mode
(*, 228.1.1.1), 00:21:47/00:03:24,
RP 1.1.1.1, flags: S
Incoming interface:
FastEthernet0/0, RPF nbr 10.1.2.1
Outgoing interface list:
Tunnel2,
Forward/Sparse, 00:21:47/00:03:24
(20.20.20.20, 228.1.1.1),
00:00:22/00:02:37, flags:
Incoming interface: Tunnel2,
RPF nbr 19.19.19.19
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 00:00:22/00:03:07
(10.19.20.20, 228.1.1.1),
00:00:22/00:02:37, flags:
Incoming interface: Tunnel2,
RPF nbr 19.19.19.19
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 00:00:22/00:03:07
(*, 224.0.1.40), 01:34:10/00:02:27,
RP 0.0.0.0, flags: DCL
Incoming interface: Null,
RPF nbr 0.0.0.0
Outgoing interface list:
FastEthernet0/0,
Forward/Sparse, 01:34:08/00:02:27
7. Ping from CE2 to 228.1.1.1 and Validate
CE2#ping 228.1.1.1
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to
228.1.1.1, timeout is 2 seconds:
Reply to request 0 from 8.8.8.8,
512 ms
SUMMARY OUTLINE of STEPS
•
Configure the Core
◦
Enable multicast routing
◦
Enable PIM on the interfaces
◦
Configure the rendezvous point
•
Configure the PE/CE
◦
CE
▪
Enable multicast routing
▪
Enable PIM on the interfaces
▪
Configure the rendezvous point
◦
PE
▪
Enable multicast routing
▪
Enable multicast routing in the vrf
▪
Enable PIM on the VRF interfaces
•
Configure MDT
◦
Configure the MDT address family in BGP
◦
Configure MDT group addresses in the VRF
◦
Configure PIM on the peering loopbacks.
REFERENCES and ADDITIONAL READING
