In a traditional Layer 2 network, switches forward Intra-VLAN data traffic based on the destination MAC address of Ethernet frames. Therefore, hosts within the same VLAN must resolve each other's MAC-IP address bindings using Address Resolution Protocol (ARP). When a host wants to open a new IP connection with a device in the same subnet and the destination MAC address is unknown, the connection initiator generates an ARP Request message. In the message, the sender provides its own MAC-IP binding information and queries the MAC address of the owner of the target IP. The ARP Request messages are Layer 2 Broadcast messages with the destination MAC address FF:FF:FF:FF:FF:FF.
EVPN Fabric is a routed network and requires a solution for Layer 2 Broadcast messages. We can select either BGP EVPN-based Ingress-Replication (IR) solution or enable Multicast routing in Underlay network. This chapter introduces the latter model. As in previous Unicast Routing section, we follow the Multicast deployment workflow of Nexus Dashboard Fabric Controller (NDFC) graphical user interface.
Figure 2-4 depicts the components needed to deploy Multicast service in the Underlay network. The default option for selecting “RP mode” is ASM (Any-Source Multicast). ASM is a multicast service model where receivers join a multicast group by sending PIM-join messages to a Multicast group-specific Rendezvous Point(s) (RP). RP is a “meeting point” to which the multicast source sends traffic and which RP forwards down to the shared tree. This process creates a shared multicast tree from RP to receiver. The multicast-enabled routers, in turn, use Protocol Independent Multicast – Sparse Mode (PIM-SM) multicast routing protocol for forwarding multicast traffic from senders to receivers. In default operation mode, PIM-SM allows receivers to switch from the shared multicast tree to the source-specific multicast tree. The other option for RP mode is Bi-directional PIM (BiDir). It is a variant of PIM-SM where multicast traffic always goes from sender to RP and from RP down to receivers over the shared multicast tree. In EVPN Fabric, Leaf switches are both multicast senders (forward local TS ARP messages) and receivers (wants to receiver remote ARP generated by TS connected to remote Leaf switches).
In our example, we create multicast group 239.1.1.0/24 using Any-Source Multicast (ASM) on both spine switches. We publish our Anycast-RPs to Leaf switches using IP address 192.168.254.1 (Loopback 251). Finally, we enable Protocol Independent Multicast (PIM) Sparse Mode on all Inter-Switch links and Loopback Interfaces.
Figure 2-5: EVPN Fabric Underlay Network Multicast Replication.
Configuration
Example 2-6 demonstrates the multicast configurations of the Spine switches. We enable the PIM protocol with the command feature pim. Then, we configure Loopback interface 251 and define the IP address as 192.168.254.1/32. We add this loopback to Unicast (OSPF) and Multicast (PIM-SM) routing processes. Besides, we enable Multicast routing on Loopback 0 and Inter-Switch interfaces. After interface configurations, we bind the RP address 192.168.254.1 to Multicast Group List 239.1.1.0/24 and create an Anycast-RP Set list where we list Spine switches sharing the RP address 192.168.254.1. Note that the switches attached to the Rendezvous Point group synchronize multicast sources registered to them. Synchronization information is accepted only for devices whose RP identifier is defined as the group's RP.
feature pim
!
interface loopback251
description Anycast-RP-Shared
ip address 192.168.254.1/32
ip router ospf UNDERLAY-NET area 0.0.0.0
ip pim sparse-mode
!
interface loopback 0
ip pim sparse-mode
!
interface ethernet 1/1-4
ip pim sparse-mode
!
ip pim rp-address 192.168.254.1 group-list 239.1.1.0/24
ip pim anycast-rp 192.168.254.1 192.168.0.11
ip pim anycast-rp 192.168.254.1 192.168.0.12
Example 2-6: Multicast Configuration - Spine-11 and Spine-12.
In Leaf switches, we first enable the PIM feature. Then, we include Loopback interfaces 0, 10, and 20 in multicast routing, as well as the Inter-Switch interfaces. Afterward, we specify the IP address of the multicast group-specific Rendezvous Point.
feature pim
!
ip pim rp-address 192.168.254.1 group-list 239.1.1.0/24
!
interface loopback 0
ip pim sparse-mode
!
interface loopback 10
ip pim sparse-mode
!
interface loopback 20
ip pim sparse-mode
!
interface ethernet 1/1-2
ip pim sparse-mode
Example 2-7: Multicast Configuration – Leaf-101 - 104.
In example 2-8, we can see that both Spine switches belong to the Anycast-RP 192.168.254.1 cluster. The RP-Set identifier IP address of Spine-11 is marked with an asterisk symbol (*). The command output also verifies that we have associated the Rendezvous Point with the Multicast Group Range 239.1.1.0/24. Example 2-9 verifies the RP-Multicast Group information from the Spine-12 perspective and the example from the Leaf-101 perspective.
Spine-11# show ip pim rp vrf default
PIM RP Status Information for VRF "default"
BSR disabled
Auto-RP disabled
BSR RP Candidate policy: None
BSR RP policy: None
Auto-RP Announce policy: None
Auto-RP Discovery policy: None
Anycast-RP 192.168.254.1 members:
192.168.0.11* 192.168.0.12
RP: 192.168.254.1*, (0),
uptime: 00:06:24 priority: 255,
RP-source: (local),
group ranges:
239.1.1.0/24
Example 2-8: RP-to-Multicast Group Mapping – Spine-11.
Spine-12# show ip pim rp vrf default
PIM RP Status Information for VRF "default"
BSR disabled
Auto-RP disabled
BSR RP Candidate policy: None
BSR RP policy: None
Auto-RP Announce policy: None
Auto-RP Discovery policy: None
Anycast-RP 192.168.254.1 members:
192.168.0.11 192.168.0.12*
RP: 192.168.254.1*, (0),
uptime: 00:05:51 priority: 255,
RP-source: (local),
group ranges:
239.1.1.0/24
Example 2-9: RP-to-Multicast Group Mapping – Spine-12.
Leaf-101# show ip pim rp vrf default
PIM RP Status Information for VRF "default"
BSR disabled
Auto-RP disabled
BSR RP Candidate policy: None
BSR RP policy: None
Auto-RP Announce policy: None
Auto-RP Discovery policy: None
RP: 192.168.254.1, (0),
uptime: 00:05:18 priority: 255,
RP-source: (local),
group ranges:
239.1.1.0/24
Example 2-10: RP-to-Multicast Group Mapping – Leaf-101
Example 2-11 confirms that we have enabled PIM-SM on all necessary interfaces. Additionally, the example verifies that Spine-11 has established four PIM adjacencies over the Inter-Switch links Ethe1/1-4. Example 2-12 presents the same information from the viewpoint of Leaf-101.
Spine-11# show ip pim interface brief
PIM Interface Status for VRF "default"
Interface IP Address PIM DR Address Neighbor Border
Count Interface
Ethernet1/1 192.168.0.11 192.168.0.101 1 no
Ethernet1/2 192.168.0.11 192.168.0.102 1 no
Ethernet1/3 192.168.0.11 192.168.0.103 1 no
Ethernet1/4 192.168.0.11 192.168.0.104 1 no
loopback0 192.168.0.11 192.168.0.11 0 no
loopback251 192.168.254.1 192.168.254.1 0 no
Example 2-11: Verification of PIM Interfaces – Spine-11.
Leaf-101# show ip pim interface brief
PIM Interface Status for VRF "default"
Interface IP Address PIM DR Address Neighbor Border
Count Interface
Ethernet1/1 192.168.0.101 192.168.0.101 1 no
Ethernet1/2 192.168.0.101 192.168.0.101 1 no
loopback0 192.168.0.101 192.168.0.101 0 no
Example 2-12: Verification of PIM Interfaces – Leaf-101.
Example 2-13 provides more detailed information about the PIM neighbors of Spine-11.
Spine-11# show ip pim neighbor vrf default
PIM Neighbor Status for VRF "default"
Neighbor Interface Uptime Expires DR Bidir- BFD ECMP Redirect
Priority Capable State Capable
192.168.0.101 Ethernet1/1 00:11:29 00:01:41 1 yes n/a no
192.168.0.102 Ethernet1/2 00:10:39 00:01:35 1 yes n/a no
192.168.0.103 Ethernet1/3 00:10:16 00:01:29 1 yes n/a no
192.168.0.104 Ethernet1/4 00:09:58 00:01:18 1 yes n/a no
Example 2-13: Spine-11’s PIM Neighbors.
The "Mode" column in Example 2-14 is the initial evidence that we have deployed the Any-Source Multicast service.
Spine-11# show ip pim group-range
PIM Group-Range Configuration for VRF "default"
Group-range Action Mode RP-address Shared-tree-range Origin
232.0.0.0/8 Accept SSM - - Local
239.1.1.0/24 - ASM 192.168.254.1 - Static
Example 2-14: PIM Group Ranges.
The following three examples shows that Multicast Group 239.1.1.0/24 is not active yet. We will get back to this after EVPN Fabric is deployed and we have implemented our first EVPN segment.
Spine-11# show ip mroute
IP Multicast Routing Table for VRF "default"
(*, 232.0.0.0/8), uptime: 00:08:38, pim ip
Incoming interface: Null, RPF nbr: 0.0.0.0
Outgoing interface list: (count: 0)
Example 2-15: Multicast Routing Information Base (MRIB) – Spine-11.
Spine-12# show ip mroute
IP Multicast Routing Table for VRF "default"
(*, 232.0.0.0/8), uptime: 00:07:33, pim ip
Incoming interface: Null, RPF nbr: 0.0.0.0
Outgoing interface list: (count: 0)
Example 2-16: Multicast Routing Information Base (MRIB) – Spine-12.
Leaf-101# show ip mroute
IP Multicast Routing Table for VRF "default"
(*, 232.0.0.0/8), uptime: 00:06:29, pim ip
Incoming interface: Null, RPF nbr: 0.0.0.0
Outgoing interface list: (count: 0)
Example 2-17: Multicast Routing Information Base (MRIB) – Leaf-101.
Next, we configure the Border Gateway Protocol (BGP) as the control plane protocol for the EVPN Fabric's Overlay Network.
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