In the example in Figure: Backup PE, the remote PE3 imports AD routes per ESI where the single-active flag is set. PE3 interprets the ethernet-segment as single-active if at least one PE sends an AD route per-ESI with the single-active flag set. MACs for a specified service and ESI are learned from a single PE, that is, the DF for that <ESI, EVI>.
The remote PE installs a single EVPN-MPLS destination (TEP, label) for a received MAC address and a backup next-hop to the PE for which the AD routes per-ESI and per-EVI are received. For example, in the following show command sample output, 00:ca:ca:ba:ca:06 is associated with the remote ethernet-segment eES 01:74:13:00:74:13:00:00:74:13. This ES is resolved to PE(192.0.2.73), which is the DF on the ES.
*A:PE3# show service id 1 fdb detail
===============================================================================
Forwarding Database, Service 1
===============================================================================
ServId MAC Source-Identifier Type Last Change
Age
-------------------------------------------------------------------------------
1 00:ca:ca:ba:ca:02 sap:1/1/1:2 L/0 06/12/15 00:33:39
1 00:ca:ca:ba:ca:06 eES: Evpn 06/12/15 00:33:39
01:74:13:00:74:13:00:00:74:13
1 00:ca:fe:ca:fe:69 eMpls: EvpnS 06/11/15 21:53:47
192.0.2.69:262118
1 00:ca:fe:ca:fe:70 eMpls: EvpnS 06/11/15 19:59:57
192.0.2.70:262140
1 00:ca:fe:ca:fe:72 eMpls: EvpnS 06/11/15 19:59:57
192.0.2.72:262141
-------------------------------------------------------------------------------
No. of MAC Entries: 5
-------------------------------------------------------------------------------
Legend: L=Learned O=Oam P=Protected-MAC C=Conditional S=Static
===============================================================================
*A:Dut-D# /show service id 1 evpn-mpls
===============================================================================
BGP EVPN-MPLS Dest
===============================================================================
TEP Address Egr Label Num. MACs Mcast Last Change
Transport
-------------------------------------------------------------------------------
10.20.1.2 131061 0 Yes 03/13/2000 11:26:29
rsvp
10.20.1.2 131062 1 No 03/13/2000 12:10:04
rsvp
10.20.1.5 131061 0 Yes 03/13/2000 11:18:23
rsvp
-------------------------------------------------------------------------------
Number of entries : 3
-------------------------------------------------------------------------------
===============================================================================
===============================================================================
BGP EVPN-MPLS Ethernet Segment Dest
===============================================================================
Eth SegId Num. Macs Last Change
-------------------------------------------------------------------------------
00:de:01:00:00:00:00:00:00:01 453 03/13/2000 12:10:14
-------------------------------------------------------------------------------
Number of entries: 1
-------------------------------------------------------------------------------
===============================================================================
*A:Dut-D# /show service id 1 evpn-mpls esi 00:de:01:00:00:00:00:00:00:01
===============================================================================
BGP EVPN-MPLS Ethernet Segment Dest
===============================================================================
Eth SegId Num. Macs Last Change
-------------------------------------------------------------------------------
00:de:01:00:00:00:00:00:00:01 453 03/13/2000 12:10:14
===============================================================================
===============================================================================
BGP EVPN-MPLS Dest TEP Info
===============================================================================
TEP Address Egr Label Last Change
Transport
-------------------------------------------------------------------------------
If PE3 sees only two single-active PEs in the same ESI, the second PE is the backup PE. Upon receiving an AD per-ES/per-EVI route withdrawal for the ESI from the primary PE, PE3 starts sending the unicast traffic to the backup PE immediately.
If PE3 receives AD routes for the same ESI and EVI from more than two PEs, the PE does not install any backup route in the datapath. Upon receiving an AD per-ES/per-EVI route withdrawal for the ESI, it flushes the MACs associated with the ESI.
On the 7210 SAS, an ES can be multi-homed to up to two PEs.