EVPN VXLAN Convergence

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Fabric Type BGP + BFD Settings Convergence (Leaf ↔ Spine) Notes
Cisco Nexus 9K (NX-OS 10.2) BFD 50/150 ms ~60–80 ms BGP PIC-core enabled
Arista 7050X3 (EOS 4.30) BFD 50/150 ms ~40 ms With ECMP and FRR active
SONiC + FRR (Tomahawk3) BFD 50/150 ms ~70 ms Depends on SAI FIB update latency
Juniper QFX EVPN BFD 10/30 ms ~30 ms Very aggressive tuning
Multi-VTEP scale (≥64 VTEPs) BFD 50/150 ms ~100–150 ms RR propagation delay dominates




Stage Description Typical Time
1. Failure Detection BFD or link-down event triggers 3–50 ms (depending on BFD interval)
2. Control Plane Reaction BGP withdraw/advertise new paths 10–100 ms
3. Route Reflector Processing (if used) Reflector recomputes and re-advertises EVPN routes 10–50 ms
4. FIB Update (Hardware) ASIC reprograms next-hops, tunnels, MAC/IP bindings 1–10 ms
➡️ Total 30–200 ms typical, depending on tuning

 


Scenario Failure Detection Total Convergence Comments
BGP Default (no BFD) 180 s (Hold timer) 180–200 s Not usable for data-center fabrics
BGP tuned (Keepalive 3s / Hold 9s) 9 s 9–12 s OK for WAN, too slow for DC
BGP + BFD (50ms/3) 150 ms 200–400 ms Used in leaf–spine & EVPN
BGP + BFD + PIC/FRR 150 ms <200 ms Target for high-performance DC fabrics



Failure Type Detected By Typical Detection Action
Physical link down Underlay BFD ~150 ms OSPF route removed, BGP session reset
Remote VTEP unreachable BFD for BGP or NVE ~200–300 ms EVPN route withdrawn
Tunnel datapath issue BFD over VXLAN ~200 ms VNI marked down
Device crash / process failure

 BFD session timeout ~150–300 ms Neighbor cleanup

interface Ethernet1/1
  no switchport
  ip address 172.16.1.1/31
  ip ospf network point-to-point
  ip ospf area 0
  bfd interval 50 min_rx 50 multiplier 3


router bgp 65000
  neighbor 10.0.0.11 bfd
  neighbor 10.0.0.12 bfd
  neighbor 10.0.0.13 bfd

interface nve1
  source-interface loopback0
  member vni 10010
    bfd interval 50 min_rx 50 multiplier 3



FRR:

 Example — BGP PIC (Prefix Independent Convergence)

This is BGP’s version of FRR:

  • Backup paths are pre-programmed in FIB.

  • When next-hop goes down, traffic shifts instantly to the backup.

  • Used heavily in EVPN/VXLAN fabrics.

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