Objectives
The simulator ticks each one as soon as the network meets it.
On S1 and S2: loopback0 (10.0.1.1, 10.0.1.2), Layer 3 links 10...2/30 on ports 1 and 2, router bgp 65000 with redistribute connected.
On L1 (AS 65001) and L2 (AS 65002): loopback0 (10.0.2.1, 10.0.2.2), loopback1 (10.10.10.1, 10.10.10.2), Layer 3 links 10...1/30 on ports 1 and 2, router bgp with redistribute connected.
Peer each leaf with each spine on the link address, with send-community extended and address-family l2vpn evpn activate.
show ip bgp summary on L1: every neighbor is Established.
L1 learns L2’s VTEP address 10.10.10.2 through BGP.
Before you start
One session per link is the simple design. Many fabrics add a second session between loopbacks for EVPN, with ebgp-multihop: this model needs the session’s path to come from a directly connected link, so it uses one session. EVPN routes keep their VTEP next hop as they cross the spine.
Concept
A leaf-spine fabric on Dell switches
Every leaf connects to every spine, and no leaf connects to another leaf, so any two leaves are two hops apart over several equal paths. eBGP routes between loopbacks form the underlay, usually with one ASN per leaf pair. EVPN then runs on the same BGP sessions: VTEPs announce their VNIs and hosts, and tunnels form from those routes. SONiC can peer without link addresses: ipv6 enable and neighbor interface are enough.
