BGP EVPN Part IV: MAC-VRF L2RIB Update: Local MAC Address

In Figure 1-3 we have VLAN 10 mapped to EVI/MAC-VRF L2VNI10000. TS-A1 (IP: 192.168.11.12/MAC: 1000.0010.beef) is connected to VLAN10 via Attachment Circuit (AC) Ethernet 1/2, (ifindex: 1a000200). 

Figure 1-3: MAC-VRF: L2RIB Local Learning Process.

Example 1-1 shows the VLAN to L2VNI mapping information. 

Leaf-101# show vlan id 10 vn-segment
VLAN Segment-id
---- -----------
10   10000       

Example 1-1: VLAN to EVPN Instance Mapping Information.

Step-1 and 2: MAC Table Update 

During the startup process, TS-A1 sends a Gratuitous ARP (GARP) message to announce its presence on the network and validate the uniqueness of its IP address. It uses its IP address in the Target IP field (Example 1-2). If another host responds to this unsolicited ARP reply, it indicates a potential IP address conflict. 

Ethernet II, Src: 10:00:00:10:be:ef, Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Address Resolution Protocol (reply/gratuitous ARP)
    Hardware type: Ethernet (1)
    Protocol type: IPv4 (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: reply (2)
    [Is gratuitous: True]
    Sender MAC address: 10:00:00:10:be:ef (10:00:00:10:be:ef)
    Sender IP address: 192.168.11.12
    Target MAC address: Broadcast (ff:ff:ff:ff:ff:ff)
    Target IP address: 192.168.11.12

Example 1-2: Gratuitous ARP from TS-A1.

Leaf-101 learns the MAC address of TS-A1 from the ingress frame and encodes the source MAC address 1000:0010:beef into the VLAN10 MAC address table (Example 1-3). The type is Dynamic, and the egress port (next-hop) is interface Ethernet 1/2. The default MAC address aging time in Cisco Nexus 9000 series switches is 1800 seconds (30 minutes). 

Leaf-101# show system internal l2fwder mac
Legend: 
        * - primary entry, G - Gateway MAC, (R) - Routed MAC, O - Overlay MAC
        age - seconds since last seen,+ - primary entry using vPC Peer-Link,
        (T) - True, (F) - False, C - ControlPlane MAC
   VLAN     MAC Address      Type      age     Secure NTFY Ports
---------+-----------------+--------+---------+------+----+------------------
*    10    1000.0010.beef   dynamic   00:03:43   F     F     Eth1/2

Example 1-3: Leaf-101 MAC Address Table.

Step-3: MAC-VRF’s L2RIB Update

The Layer 2 Forwarder (L2FWDER) component detects the new MAC address in the VLAN 10 Bridge Table. The L2FWDER registers this as a MAC move event, prompting it to program the MAC address reachability information into the Layer 2 Routing Information Base (L2RIB) associated with the MAC-IP VRF of tenant TENANT77. Examples 1-4 show, starting from the bottom, how the L2FWDER component first detects a new MAC address, 1000.0010.beef, associated with VLAN 10 over an Attachment Circuit 0x1a000200 (Ethernet1/2, Example 1-5). It adds a new local MAC route to the topology 10 (L2VNI 10000) with the next-hop interface ID 0x1a000200 (Ethernet1/2).

l2fwder_dbg_ev, 690 l2fwder_l2rib_add_delete_local_mac_routes,
154Adding route  topo-id: 10, macaddr: 1000.0010.beef, nhifindx: 0x1a000200
l2fwder_dbg_ev, 690 l2fwder_l2rib_mac_update,
739MAC move 1000.0010.beef (10) 0x0 -> 0x1a000200

Example 1-4: L2RIB Update by L2FWDER.

Example 1-5 verifies the snmp-ifindex 0x1a000200 mapping to physical interface Ethernet1/2.

Leaf-101# show interface snmp-ifindex | i 0x1a000200

Eth1/2          436208128  (0x1a000200)

Example 1-5: SNMP-ifindex to Interface Mapping Verification.

The examples 1-6 demonstrate the L2FWDER component process. An illustration below details the update events from the L2RIB perspective. The L2RIB receives the MAC route 1000.0010.beef (topology 10) and creates a new MAC route after a MAC mobility check. The route is then added to L2VNI 10000 and marked as a local route (rt_flags=L) with the next-hop interface Ethernet1/2.

Leaf-101# sh system internal l2rib event-history mac | i beef
Rcvd MAC ROUTE msg: (10, 1000.0010.beef), vni 0, admin_dist 0, seq 0, soo 0, 
(10,1000.0010.beef):Mobility check for new rte from prod: 3
(10,1000.0010.beef):Current non-del-pending route local:no, remote:no, linked mac-ip count:1
(10,1000.0010.beef):Clearing routelist flags: Del_Pend, 
(10,1000.0010.beef,3):Is local route. is_mac_remote_at_the_delete: 0
(10,1000.0010.beef,3):MAC route created with seq 0, flags L, (), 
(10,1000.0010.beef,3): soo 0, peerid 0, pc-ifindex 0
(10,1000.0010.beef,3):Encoding MAC best route (ADD, client id 5)
(10,1000.0010.beef,3):vni:10000 rt_flags:L, admin_dist:6, seq_num:0 ecmp_label:0 soo:0(--)
(10,1000.0010.beef,3):res:Regular esi:(F) peerid:0 nve_ifhdl:1224736769 mh_pc_ifidx:0 nh_count:1
(10,1000.0010.beef,3):NH[0]:Eth1/2

Example 1-6: L2RIB from the L2RIB Perspective.

Figure 1-7 shows that the MAC address of TS-A1 is installed into the L2RIB associated with topology 10 (VN segment 10000). The entry is marked as a locally learned route (Prod=Local, Flag=L), with the interface Ethernet 1/2 set as the next hop for the MAC address.

Leaf-101# show l2route evpn mac evi 10
Flags -(Rmac): Router MAC (Stt):Static (L):Local (R):Remote (V):vPC link
(Dup):Duplicate (Spl):Split (Rcv):Recv (AD):Auto-Delete (D):Del Pending
(S):Stale (C):Clear, (Ps):Peer Sync (O):Re-Originated (Nho):NH-Override
(Pf):Permanently-Frozen, (Orp): Orphan
Topology    Mac Address    Prod   Flags         Seq No     Next-Hops
----------- -------------- ------ ------------- ---------- -----------------
10          1000.0010.beef Local  L,            0          Eth1/2

Example 1-7: Updated L2RIB.

Next, L2RIB Update, MAC-IP binding.