Switch Stacking (CISCO)

Intro To Stacking

Switch stacking combines multiple switches into one logical switch. Can create redundancy, better port usage etc.

EtherChannel must be between two devices (NEXUS can use VPC) and will not work with 3 or move devices.

MEC or multi-chassis EtherChannel can be used to allow this if the switches are stacked.

Access switches can be stacked as well but is generally different.

When configuring the switch, you are using the config on the active switch and the config is synced between the two.

This centralizes the management and control planes while distributing the data plane.

Interface Numbering

When stacking switches port interface numbers follow this convention:

switch/slot/interface

G1/0/2

G2/0/1

If a SFP+ card installed it might look like this G1/1/1

VSS Virtual Switching System

Allows up to 2 switches to stack

Only supported on switches that are end of sale/end of life.

VSL

Stack is connected via a virtual switch link (VSL)

10/40G interface needed, can use fiber or supervisor cards.

VSL passes to types of traffic:

VSS Control - used to establish the VSS

Data - Only when it must be send to the other member to be send on a port that is on that member only.

Virtual Switch Link Protocol (VSLP) - Is used to establish and maintain the VSL/VSS

• Uses two protocols LMP and RRP

LMP

• Verifies link Integrity
• Exchanges Switch IDs

RRP

• Determines if switches are compatible (software and hardware).
• Determines which one will be standby and active.

Can Choose one of two modes.

• RPR - Route Processor Redundancy Mode
• Standby cannot forward, only hot spare.
• NSF/SSO - Non Stop Forwarding/Stateful switchover
• Standby switch can forward traffic.

STACKWISE

Allows up to 8/(older can do 9) switches to be stacked.

3750/3850 and 9200/9300

Uses dedicated stack cables to form a ring topology, can be high speed up to 1Tb/s.

Can use stack power cables.

SDP - Stack Discovery Protocol

• Uses broadcast messages to discover stack topology
• Creates a unique ID for each switch, can be manually changed.

Initialization

Switches will be added if they boot within a 2min election window.

Uses priority then MAC (lowest).

Active and standby are chosen then the rest are members.

Election is not triggered when a new switch is added.

STACKWISE VIRTUAL

Allows two switches to form a virtual switch, similar to the old VSS.

Supported on 9400-9600 series switches

Stackwise Virtual Link - (SVL)

• Acts the same as the VSL in VSS
• Can use 10G-100G+
• Can support km apart over fiber

Passes two kinds of traffic

• Stackwise Virtual Control Traffic - Used to establish and maintain the virtual domain
• Data - Same as VSS

Frames are encapsulated with a 64 Byte Stackwise Virtual header.

Initialization

Link Managment Protocol (LMP)

• Establishes bidirectional traffic forwarding
• Sends hello messages
• Other info

Stackwise Discovery Protocol (SDP)

• Determines hardware and software compatibility
• Determines active and standby

In Stackwise virtual both switches can forward but only one is the management/control plane.