RFC 7432 and the Nokia SR OS EVPN implementation use Algorithm-1 for DF election when the “default” algorithm is left in place.

1. Every PE attached to the same ES advertises a DF-Preference in its Ethernet-Segment route; the PE with the numerically lowest preference becomes DF.

2. If two or more PEs have the same preference, the tie-breaker is the numerically lowest originating-router IP address.

In the exhibit PE-2 advertises DF-Preference 100, while PE-1 and PE-3 advertise 32767 (default) and PE-4 advertises 200. Because 100 is the smallest value, PE-2 wins and is elected the DF for VPLS 10 on ESI-1.

A. PE1’s DF-Preference (32767) is higher than PE2’s 100, so it loses in the first comparison step.

C. PE3’s DF-Preference (32767) is higher than PE2’s 100, so it is not chosen.

D. PE4 advertises preference 200, higher than PE2’s 100, so it is not selected.

1. IETF RFC 7432 “BGP MPLS-based Ethernet VPN”, Sec. 8.5.1-8.5.2, pp. 33-34 – DF-Preference and tie-breaker rules.

2. Nokia SR OS 22.10.R1 EVPN Guide, Sec. “Designated Forwarder Election”, pp. 110-112 – default Algorithm-1 behaviour and preference values.

3. Nokia “Virtualized Services Fundamentals” Courseware (4A0-115), Module 4, pp. 4-35 to 4-36 – example showing PE with lowest DF-Preference elected DF.