EVPN defines a mechanism to protect the EVPN service from control plane churn as a result of loops or accidental duplicated MAC addresses. The 7750 SR, 7450 ESS, and 7950 XRS support an enhanced version of this procedure as described in this section.
A situation may arise where the same MAC address is learned by different PEs in the same VPLS because of two (or more hosts) being misconfigured with the same (duplicate) MAC address. In such situation, the traffic originating from these hosts would trigger continuous MAC moves among the PEs attached to these hosts. It is important to recognize such situation and avoid incrementing the sequence number (in the MAC Mobility attribute) to infinity.
To remedy such situation, a router that detects a MAC mobility event by way of local learning starts a window <in-minutes> timer (default value of window = 3) and if it detects num-moves <num> before the timer expires (default value of num-moves = 5), it concludes that a duplicate MAC situation has occurred. The router then alerts the operator with a trap message. The offending MAC address can be shown using the show service id svc-id bgp-evpn command:
10 2014/01/14 01:00:22.91 UTC MINOR: SVCMGR #2331 Base
"VPLS Service 1 has MAC(s) detected as duplicates by EVPN mac-
duplication detection."
# show service id 1 bgp-evpn
===============================================================================
BGP EVPN Table
===============================================================================
MAC Advertisement : Enabled Unknown MAC Route : Disabled
VXLAN Admin Status : Enabled Creation Origin : manual
MAC Dup Detn Moves : 5 MAC Dup Detn Window: 3
MAC Dup Detn Retry : 9 Number of Dup MACs : 1
-------------------------------------------------------------------------------
Detected Duplicate MAC Addresses Time Detected
-------------------------------------------------------------------------------
00:00:00:00:00:12 01/14/2014 01:00:23
-------------------------------------------------------------------------------
===============================================================================
After detecting the duplicate, the router stops sending and processing any BGP MAC advertisement routes for that MAC address until one of the following occurs:
The MAC is flushed because of a local event (SAP or SDP binding associated with the MAC fails) or the reception of a remote update with better SEQ number (because of a MAC flush at the remote router).
The retry <in-minutes> timer expires, which flushes the MAC and restart the process.
The values of num-moves and window are configurable to allow for the required flexibility in different environments. In scenarios where BGP rapid-update evpn is configured, the operator may want to configure a shorter window timer than in scenarios where BGP updates are sent every (default) min-route-advertisement interval.
MAC duplication is always enabled in EVPN-VXLAN VPLS services, and the preceding described mac duplication parameters can be configured per VPLS service under the bgp-evpn mac-duplication context:
*A:DGW1>config>service>vpls>bgp-evpn# info
----------------------------------------------
mac-advertisement
unknown-mac-route
mac-duplication
detect num-moves num window in_mins
[no] retry in_mins
vxlan bgp 1 vxlan-instance 1
no shutdown
exit