VSS on Cisco 4500/4500X Switches

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The VSSCisco Virtual Switching System is a clustering technology that pools two Cisco Catalyst 4500-E Series Switches with Cisco Catalyst Supervisor Engine 7-E or 7-LE or two Catalyst 4500-X Series Switches into a single virtual switch. In a VSS, the data plane of both clustered switches is active at the same time in both chassis. VSS members are connected by virtual switch links (VSLs) using standard Gigabit or 10 Gigabit Ethernet connections between the VSS members. VSLs can carry regular user traffic in addition to the control plane communication between the VSS members.

While a similar technology (Multi-Chassis Etherchannel, MEC) exists in Nexus datacenter switches known as vPC, the Nexus switches only appear to other adjacent switches as one switch across L2 links while maintaining two separate control planes and management points. VSS actually does a better job of emulating a single switch with one active, and one (or more) standby control plane allowing it to fully support a dual-homed L3 routed link. If you are familiar with Cisco Stackwise technology in 3750/3850 switches, VSS is probably more comparable to those except VSS only supports up to two switches and instead of using Stackwise cables, it uses multiple 10G links for interconnecting switches (i.e. VSL).

How to configure a VSS for the Catalyst 4500 series switch (Supervisor Engine 7-E, Supervisor Engine 7L-E, IOS-XE 3.6.0 does support VSS on Sup8.)?

Physical vs. Logical Topology in a VSS Configuration


Before finishing VSS configuration for Cisco 4500 series switches, you need to know the basic requirement.




  • Supervisor Engine 7-E (WS-X45-Sup7-E) (IP Base)
  • Or Supervisor Engine 7L-E (WS-X45-Sup7L-E) (Enterprise Services)
  • Or 4500X Switch Family (IP Base)
  • Minimum IOS XE 3.4.xSG
  • IOS XE 3.5.0E for L3 MEC and Fast Hello Dual-Active Detection support (Recommended)

License requirement

Feature LAN Base IP Base Enterprise Service
  • Virtual Switching System /VSS
No Yes
(SUP7E only)
  • Support for Layer 3 MEC—VSS with Layer 3 Multichassis EtherChannel (MEC) at the aggregation layer
  • Support for VSLP Fast Hello—With VSLP Fast Hello, the Catalyst 4500-X configured for VSS can now connect Access Switches that do not support the ePAgP protocol.
  • Support for VSL Encryption
  • Support for Asymmetrix chassis
No Yes (SUP7E)


Yes (SUP7E)

Yes (SUP7LE)

Note: Please check Cisco documentation for more detail. To know more on license requirement refer Release Notes for the Catalyst 4500E Series Switch”

  1. Single-sup cross-chassis VSS support: Yes.
  2. Quad-sup VSS configuration with in-chassis redundant sups: In-chassis redundant sups in rommon mode with active uplinks.
  3. It also supports 10 Gigabit Ethernet Virtual Switch Link (VSL) and 1 Gigabit Ethernet VSL.
  4. SSO and nonstop forwarding (NSF) must be configured on each switch. If a VSS does not meet the requirements for SSO redundancy; it will be incapable of establishing a relationship with the peer switch. Catalyst 4500/4500-X series switches’ VSS does not support route processor redundancy (RPR) mode.

Cabling Between Chassis

  1. Minimum of two 10Gbps links with at least one on the Supervisor (4500 Only)
  2. Minimum of one (more is recommended) 1Gbps or 10Gbps links for dual-active detection

Dual Active Detection Method

Only Enhanced PAgP used to be supported but, as of 3.5.0E, Fast Hello is made available.  EPAgP requires a downstream switch that is EPAgP-capable, which is sometime hard to find. Here we choose to use Fast Hello, although more than one method can be configured.

Also, you can read the Cisco 4500 VSS Requirement-Software, Hardware and Licensing


Configuration Steps-VSS on Cisco 4500/4500X Switches:

Make sure all cabling between two switches are completed before proceeding

On Switch 1

1. Configure virtual domain then save config

VSS on Cisco 4500-4500X Switches01


2. Configure VSL links. 

VSS on Cisco 4500-4500X Switches02


3. Convert switch to VSS mode. Confirm and switch will reload


switch convert mode virtual



On Switch 2

1. Configure virtual domain then save config

VSS on Cisco 4500-4500X Switches04


2. Configure VSL links. 

VSS on Cisco 4500-4500X Switches05


3. Convert switch to VSS mode. Confirm and switch will reload


switch convert mode virtual


  • Wait until switch 2 comes back and join VSS
  • You can only make config changes on the active supervisor/switch now


On the active switch

1. Adjust switch priority


configure terminal

switch virtual domain 1

 switch 1 priority 110

 switch 2 priority 100



2. Configure dual-active detection

VSS on Cisco 4500-4500X Switches08

More Related

Cisco Catalyst 4500-X Series Switch Family

Cisco 4500 VSS Requirement-Software, Hardware and Licensing

Cisco Catalyst 4500E Supervisor Engine 8-E Review

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