Administrator Guide

Flex Hash and Optimized Boot-Up
This chapter describes the Flex Hash and fast-boot enhancements.
Topics:
• Flex Hash Capability Overview
• Configuring the Flex Hash Mechanism
• LACP Fast Switchover
• Configuring LACP Fast Switchover
• LACP
• RDMA Over Converged Ethernet (RoCE) Overview
• Sample Configurations
• Preserving 802.1Q VLAN Tag Value for Lite Subinterfaces
Flex Hash Capability Overview
The flex hash functionality enables you to configure a packet search key and matches packets based on the search key. When a packet
matches the search key, two 16-bit hash fields are extracted from the start of the L4 header and provided as inputs (bins 2 and 3) for
RTAG7 hash computation. You must specify the offset of hash fields from the start of the L4 header, which contains a flow identification
field.
You can configure the system to include the fields present at the offsets that you define (from the start of the L4 header) as a part of
LAG and ECMP computation. Also, you can specify whether the IPv4 or IPv6 packets must be operated with the Flex Hash mechanism.
Keep the following points in mind when you configure the flex hash capability:
• A maximum of eight flex hash entries is supported.
• A maximum of 4 bytes can be extracted from the start of the L4 header.
• The offset range is 0 – 30 bytes from the start of the L4 header.
• Flex hash uses the RTAG7 bins 2 and 3 (overlay bins). These bins must be enabled for flex hash to be configured.
• If you configure flex hash by using the load-balance ingress-port enable and the load-balance flexhash
commands, the show ip flow and show port-channel-flow commands are not operational. Flex hash settings and these
show commands are mutually exclusive; only one of these capabilities can be functional at a time.
Configuring the Flex Hash Mechanism
The flex hash functionality enables you to configure a packet search key and matches packets based on the search key. When a packet
matches the search key, two 16-bit hash fields are extracted from the start of the L4 header and provided as inputs (bins 2 and 3) for
RTAG7 hash computation. You must specify the offset of hash fields from the start of the L4 header, which contains a flow identification
field.
1. You can enable bins 2 and 3 by using the load-balance ingress-port enable command in Global Configuration mode. To
configure the flex hash functionality, you must enable these bins.
CONFIGURATION mode
Dell(conf)# load-balance ingress-port enable
When load balancing RRoCE packets using flex hash is enabled, the show ip flow command is disabled. Similarly, when the show
ip flow command is in use (ingress port-based load balancing is disabled), the hashing of RRoCE packets is disabled.
Flex hash APIs do not mask out unwanted byte values after extraction of the data from the Layer 4 headers for the offset value.
2. Use the load-balance flexhash command to specify whether IPv4 or IPv6 packets must be subjected to the flex hash
functionality, a unique protocol number, the offset of hash fields from the start of the L4 header to be used for hash calculation, and a
meaningful description to associate the protocol number with the name.
CONFIGURATION mode
17
354 Flex Hash and Optimized Boot-Up