Data Center Network Design
This domain covers Juniper QFX data center design: spine-leaf, EVPN-VXLAN, IP fabric, and DC interconnect.
Core rules
- Build a spine-leaf IP fabric with eBGP underlay; use ECMP and avoid STP in the fabric.
- Use EVPN-VXLAN overlay for Layer 2 extension and multi-tenancy.
- Prefer symmetric IRB and anycast gateway for consistent routing.
- Design for oversubscription and scale: 100G or 400G spines, 25G or 100G leaves.
- Add MC-LAG only where needed; use EVPN multihoming where possible.
Worked example
A company needs two data centers with 16 racks each and VM mobility. Design: 4 spine and 16 leaf QFX switches per DC, eBGP underlay, EVPN-VXLAN overlay, anycast gateway, symmetric IRB, and DCI via EVPN Type-5 routes. Reason: IP fabric gives ECMP and no STP blocking; EVPN supports MAC mobility and multi-tenancy; symmetric IRB keeps routing consistent across VTEPs.
Traps
- Running STP in a spine-leaf fabric.
- Asymmetric IRB causing policy and routing inconsistency.
- Undersizing ECMP or oversubscribing spines.
- Extending VLANs between DCs without a scale plan.