Introducing Cisco StackWise Virtual (SV): An Overview

Introducing Cisco StackWise Virtual (SV): An Overview

From the viewpoints of the network control plane and administration, StackWise Virtual (SV) merges two switches into a single logical network unit. When one of the devices fails over, it employs Cisco IOS Stateful Switchover (SSO) technology and Non-Stop Forwarding (NSF) extensions to routing protocols to offer flawless traffic failover. A StackWise Virtual domain appears to nearby devices as a single logical switch or router.

Stackwise Virtual
Fig 1.1- Cisco Stackwise Virtual

Key business benefits of the SVL

  • Lowered risk brought on by a looping topology Continuous business communication using a redundant chassis and supervisors with SSO capabilities
  • More bandwidth from the access layer provides a better return on current investments.
  • First Hop Redundancy Protocols (FHRP), such as the Hot Standby Routing Protocol (HSRP), the GLBP, and the VRRP, are eliminated and setup problems are reduced.
  • Management of a single configuration is simplified, and there are fewer operational failure spots.

StackWise Virtual Management

All network and device resources may be managed centrally using StackWise Virtual domain. This covers Layer 2 protocols like Spanning Tree Protocol (STP), Unidirectional Link Detection Protocol (UDLD), Flow Control, and LACP as well as Layer 3 protocols like Open Shortest Path First (OSPF), Improved Interior Gateway Routing Protocol (EIGRP), and Border Gateway Protocol (BGP).

When accessible through management IP or console, StackWise Virtual domain is chosen as the primary management location for the entire system.

The SV active switch is the switch serving as the only management point. The SV standby switch is also known as the peer chassis. The SV standby switch is also known as a hot-standby switch since it is prepared to take over all operations and become the active switch in the event that the active switch is compromised.

StackWise Virtual link Initialization

The switch will become the active switch for the StackWise Virtual domain must be determined during activation. The StackWise Virtual connection has to be setup and brought online for control plane communication in order to identify the active and standby roles. The responsibilities must be discussed very early during the switch bootup cycle since this choice influences how each switch behaves.

As a result, the system must bring the StackWise Virtual link and its associated ports online before initializing the rest of the system.

Internal messaging transmitted through the StackWise Virtual connection facilitates communication between the two switches. The link is robust to single-link failures since it is constructed as an EtherChannel interface. Before activating the StackWise Virtual domain, the system must bring the StackWise Virtual link online.
  • Pre-parse configuration file to discover the stack and bring up SVL interfaces
  • Link Management Protocol (LMP) used to check the integrity of SVL links and send periodic hello messages to maintain the communication
  • StackWise Discovery Protocol (SDP) used to determine the compatible hard- ware and software version to form the SVL and to determine which switch becomes active or standby from the control plane perspective
The switch detects which ports on its system are members of the StackWise Virtual link, and the configuration file is prepared to extract the required StackWise Virtual link instructions and interfaces.
  • The Link Management Protocol (LMP) is activated on each link of the StackWise Virtual link as soon as it is brought up online. 
  • Verifies link integrity by establishing bidirectional traffic forwarding, and rejects any unidirectional links
  • Exchanges periodic hellos to monitor and maintain the health of the links
  • Negotiates the version of StackWise Virtual header between the switches

StackWise Virtual link role resolution

The StackWise Discovery Protocol determines each switch's redundancy duty. Determines if the hardware and software versions support the formation of a Cisco StackWise Virtual domain. 

From a control-plane standpoint, this determines which switch will become the active virtual switch and which will become the standby virtual switch.

High-availability role determination

The active role is decided first during role resolution, and only then does the other switch, which has the function of member, go through compatibility tests, followed by bulk configuration sync. The SSO mechanism then causes the switch to go into standby mode.

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