Users Guide

266 Stacking
NSF Network Design Considerations
A network can be designed to take maximum advantage of NSF. For example,
by distributing a LAG's member ports across multiple units, the stack can
quickly switch traffic from a port on a failed unit to a port on a surviving unit.
When a unit fails, the forwarding plane of surviving units removes LAG
members on the failed unit so that it only forwards traffic onto LAG members
that remain up. If a LAG is left with no active members, the LAG goes down.
To prevent a LAG from going down, configure LAGs with members on
multiple units within the stack, when possible. If a stack unit fails, the system
can continue to forward on the remaining members of the stack.
If the switch stack performs VLAN routing, another way to take advantage of
NSF is to configure multiple “best paths” to the same destination on
different stack members. If a unit fails, the forwarding plane removes Equal
Cost Multipath (ECMP) next hops on the failed unit from all unicast
forwarding table entries. If the cleanup leaves a route without any next hops,
the route is deleted. The forwarding plane only selects ECMP next hops on
surviving units. For this reason, try to distribute links providing ECMP paths
across multiple stack units.
Why is Stacking Needed?
Stacking increases port count without requiring additional configuration. If
you have multiple Dell EMC Networking N-Series switches, stacking them
helps make management of the switches easier because you configure the
stack as a single unit and do not need to configure individual switches.
Default Stacking Values
Stacking is always enabled on Dell EMC Networking N-Series switches.
On the Dell EMC Networking N1100-ON/N1500 Series switches, by default,
the 10G SFP+ ports are in Ethernet mode and must be configured to be used
as stacking ports. Ports that are configured in stacking mode show as
“detached” in the output of the show interfaces status command.
NOTE: N1124T-ON/N1148T-ON/N1124P-ON/N1148P-ON/N1500 10G SFP+ ports
may only be configured as stacking in adjacent pairs, e.g. Te1/0/1 and Te1/0/2. If
configuring all four ports as stacking, the pairs of stacking links must be connected
to the same unit, i.e. both Te1/0/1-2 must connect to a single adjacent stack unit.