Arista EVPN VXLAN Configuration Example (1b) - eBGP Underlay

Before start, let's talk a bit regarding the underlay vs overlay. This topic is very well covered in the EVPN Deployment Guide.  Here is my easy understanding:

• The underlay is:
• EBGP between Spine and Leafs over P2P links. Of course, IGP is an option. 
• To advertise the routing information of the VTEPs' and Spines' loopbacks for
• EVPN peering sessions
• The source/destination address Vxlan data traffic
• You can use different loopback for EVPN and Vxlan
• In EVPN Deployment Guide (page 20), lo0 for EVPN peering, lo1 for VxLAN
• In this blog, I use the same loopback160 for both
• Overlay control plane is BGP EVPN, to 
• Register the VTEP (type 3), it is like L2vpn autodiscovery. 
• Carry EVPN prefixes L2 and L3

Topology and Configuration:

Explanation:

• EVPN is only supported in BGP multi-agent mode. 
• Simple EBGP peering over b2b ethernet interfaces
• All routers advertise the loopback160 /32 address
• Please note, the spine routers/RR have a route-map to control, so that only /32 loopback prefixes within 160.255.255.0/24 are advertised. 
• The b2b interface addresses are not needed in the data plane, so unnecessary for routing protocol. 
• And this eBGP setup implies that interface address can be duplicated in different POP/DC. A big plus for automation 

Control Plane Verification:
1) show ip bgp sum on VTEP1, and please note only 2 bgp routes

snp261-eVtep1#sh ip bgp sum
BGP summary information for VRF default
Router identifier 160.255.255.10, local AS number 65161
Neighbor Status Codes: m - Under maintenance
  Description              Neighbor         V  AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down State   PfxRcd PfxAcc
  eUnder-Sp1               160.1.10.1       4  65100          23840     23848    0    0   13d17h Estab   2      2

2) show ip bgp on VTEP1 to check the bgp prefixes, 1 for spine, 1 from VTEP2

snp261-eVtep1#show ip bgp
          Network                Next Hop              Metric  LocPref Weight  Path
 * >      160.255.255.1/32       160.1.10.1            0       100     0       65100 i
 * >      160.255.255.10/32      -                     -       -       0       i
 * >      160.255.255.20/32      160.1.10.1            0       100     0       65100 65162 i

3) show bgp prefix of VTEP2's loopback on VTEP1

snp261-eVtep1#sh ip bgp 160.255.255.20
BGP routing table information for VRF default
Router identifier 160.255.255.10, local AS number 65161
BGP routing table entry for 160.255.255.20/32
 Paths: 1 available
  65100 65162
    160.1.10.1 from 160.1.10.1 (180.255.255.1)
      Origin IGP, metric 0, localpref 100, weight 0, received 23:22:11 ago, valid, external, best
      Rx SAFI: Unicast

4) show ip route on VTEP1 to ensure bgp route in routing table

snp261-eVtep1#show ip route 160.255.255.20/32
 B E      160.255.255.20/32 [200/0] via 160.1.10.1, Ethernet13

5) VTEP1 pings VTEP2's lo160 - 160.255.255.20

snp261-eVtep1#ping 160.255.255.20 source lo160
PING 160.255.255.20 (160.255.255.20) from 160.255.255.10 : 72(100) bytes of data.
80 bytes from 160.255.255.20: icmp_seq=1 ttl=63 time=0.248 ms
80 bytes from 160.255.255.20: icmp_seq=2 ttl=63 time=0.128 ms
80 bytes from 160.255.255.20: icmp_seq=3 ttl=63 time=0.087 ms
80 bytes from 160.255.255.20: icmp_seq=4 ttl=63 time=0.082 ms
80 bytes from 160.255.255.20: icmp_seq=5 ttl=63 time=0.091 ms

--- 160.255.255.20 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.082/0.127/0.248/0.062 ms, ipg/ewma 0.179/0.184 ms

At this step, we are pretty sure the underlay is ready because the overlay bgp evpn peering is based on VTEPs' loopback interfaces.