Deployment Guide
Table Of Contents
- 1 Introduction
- 2 Hardware overview
- 3 Leaf-spine overview
- 4 Protocols used in the leaf-spine examples
- 5 Layer 3 configuration planning
- 6 Example 1: Layer 3 with Dell EMC leaf and spine switches using OSPF
- 7 Example 2: Layer 3 with Dell EMC leaf and spine switches using eBGP
- A Dell EMC Networking ONIE switch factory default settings
- B Validated hardware and operating systems
- C Technical support and resources
- D Support and Feedback
10 Dell EMC Networking Layer 3 Leaf-Spine Deployment and Best Practices with OS10 | Version 1.0
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4.3 Uplink Failure Detection (UFD)
If a leaf switch loses all connectivity to the spine layer, by default the attached hosts continue to send traffic to
that leaf without a direct path to the destination. The VLTi link to the peer leaf switch handles traffic during
such a network outage, but this is not considered a best practice.
Dell EMC recommends enabling UFD, which detects the loss of upstream connectivity. An uplink state group
is configured on each leaf switch, which creates an association between the uplinks to the spines and the
downlink interfaces.
In the event all uplinks fail on a switch, UFD automatically shuts down the downstream interfaces. This
propagates to the hosts attached to the leaf switch. The host then uses its link to the remaining switch to
continue sending traffic across the leaf-spine network.
4.3.1 UFD vs. iBGP at the leaf layer
Some leaf and spine implementations make use of iBGP between leaf switches instead of UFD. If UFD is not
used, it is possible, due to hashing, for packets to enter a leaf switch which does not have functioning uplinks.
If iBGP is enabled between the leaf switches, it is possible for them to route packets to each other, provided
there are valid routes. However, the designs in this document make use of UFD, because it reduces network
and configuration complexity and simplifies path determination.
VLTi
Server 2
Po 1
VLTi
Server 2
Po 1
iBGP between leaf
switches
UFD used on leaf
switches
Spine 1 Spine 2
Spine 1 Spine 2
Leaf 1
Leaf 2
Leaf 1
Leaf 2
L3 Connection
L2 Connection
Traffic path
Using iBGP between leaf switches vs UFD on leaf switches provides more path options at the
cost of greater network and configuration complexity
4.4 Rapid Spanning Tree Protocol (RSTP)
As a precautionary measure, Dell EMC recommends enabling RSTP on all switches that have layer 2
interfaces. Even though VLT environments are loop-free, STP should be configured as a best practice in case