White Papers

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
• Configuring Fast Boot and LACP Fast Switchover
• Optimizing the Boot Time
• Interoperation of Applications with Fast Boot and System States
• RDMA Over Converged Ethernet (RoCE) Overview
• 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. In Dell EMC Networking OS Release 9.3(0.0), 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
DellEMC(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.
16
Flex Hash and Optimized Boot-Up 337