Deployment Guide

15 Leaf-Spine Deployment and Best Practices Guide | Version 1.0
Dell EMC recommends enabling fast fall-over with BGP. Fast fall-over terminates external BGP sessions of
any directly adjacent peer if the link to reach the peer goes down without waiting for the hold-down timer to
expire.
Note: BGP fast fall-over is enabled manually on Dell EMC switches and is enabled by default on Cisco
Nexus 5600 series switches.
Examples using EBGP (BGPv4) are provided in the layer 3 topology examples in this guide.
5.4.2 OSPF
OSPF is an interior gateway protocol that provides routing inside an autonomous network. OSPF routers send
link-state advertisements to all other routers within the same autonomous system areas. While generally more
memory and CPU intensive than BGP, OSPF may offer faster convergence. OSPF is often used in smaller
networks. Examples using OSPF (OSPFv2 for IPv4) are provided in the layer 3 topology examples in this
guide.
5.4.3 IS-IS
IS-IS, like OSPF, is a link-state routing protocol that computes the best path through the network. Though
supported, the protocol is not as widely used and is not covered in this document. To use IS-IS for routing,
consult the applicable switch’s user guide.
5.5 BFD
BFD is a protocol used to rapidly detect communication failures between two adjacent systems over a layer 3
link. It is a simple and lightweight replacement for existing routing protocol link state detection mechanisms.
Though optional, use of BFD is considered a best practice for optimizing a leaf-spine network.
BFD provides forwarding path failure detection times on the order of milliseconds rather than seconds as with
conventional routing protocols. It is independent of routing protocols and provides a consistent method of
failure detection when used across a network. Networks converge faster because BFD triggers link state
changes in the routing protocol sooner and more consistently.
Dell EMC Networking has implemented BFD at layer 3 with user datagram protocol (UDP) encapsulation.
BFD is supported with routing protocols including BGP, OSPF and IS-IS.