Overview
Release 15.5(1)SY is a long-term maintenance release for the Catalyst 6500 platform, focused on software stability, defect resolution, and sustained hardware support, with no significant new hardware features in most later revisions.
Important Operational Note
Redundant configurations require identical supervisor engines.
If two different supervisor engines are installed, one becomes active while the other remains in a reset state.
Chronological List of Releases
The 15.5SY train includes the following maintenance releases:
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15.5(1)SY16 — 25 September 2025
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15.5(1)SY15 — 8 May 2025
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15.5(1)SY14 — 26 September 2024
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15.5(1)SY13 — 20 March 2024
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15.5(1)SY12 — 15 September 2023
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15.5(1)SY11 — 21 March 2023
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15.5(1)SY10 — 17 September 2022
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15.5(1)SY9 — 17 March 2022
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15.5(1)SY8 — 16 September 2021
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15.5(1)SY7 — 18 March 2021
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15.5(1)SY6 — 18 September 2020
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15.5(1)SY5 — 18 March 2020
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15.5(1)SY4 — 12 September 2019
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15.5(1)SY3 — 27 March 2019
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15.5(1)SY2 — 17 September 2018
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15.5(1)SY1 — 8 March 2018
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15.5(1)SY — 22 May 2017
Supported Hardware
This section describes hardware supported by the 15.5(1)SY software train. Hardware includes supervisor engines, policy feature cards (PFCs), distributed forwarding cards (DFCs), centralized forwarding cards (CFC), switching modules, transceivers, service modules, power supplies, and chassis.
Supervisor Engines
| Product ID | Description | Minimum Software |
|---|---|---|
| C6800-SUP6T | Supervisor Engine 6T with PFC4 | 15.3SY |
| C6800-SUP6T-XL | Supervisor Engine 6T with PFC4XL | 15.3SY |
| VS-S2T-10G-XL | Supervisor Engine 2T-10GE with PFC4XL | 15.0SY |
| VS-S2T-10G | Supervisor Engine 2T-10GE with PFC4 | 15.0SY |
(Additional supported hardware tables follow the same format and remain consistent with the original documentation.)
Unsupported Hardware
Hardware components not listed in the supported hardware section are not supported by the 15.5SY train and remain inactive if detected.
Images and Feature Sets
Multiple images and feature sets are available in the 15.5SY train.
Some images include encryption capabilities which may be subject to regional regulatory requirements.
EFSU Compatibility
Enhanced Fast Software Upgrade (EFSU) compatibility depends on the starting and target software versions. Only version combinations listed as compatible support non-disruptive or reduced-disruption upgrade behavior.
Software Behavior Changes
Behavior changes describe operational adjustments or documentation updates introduced throughout the 15.5SY train. These may affect existing configurations and should be reviewed before upgrading.
New Features by Release
15.5(1)SY16 – 25 Sep 2025
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No new hardware or software features introduced in this revision.
15.5(1)SY15 – 8 May 2025
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No new hardware or software features introduced.
15.5(1)SY14 – 26 Sep 2024
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No new hardware or software features introduced.
15.5(1)SY13 – 20 Mar 2024
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No new hardware or software features introduced.
15.5(1)SY12 – 15 Sep 2023
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No new hardware or software features introduced.
15.5(1)SY11 – 21 Mar 2023
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Software enhancement: Data sanitization support compliant with NIST purge methods.
15.5(1)SY10 – 17 Sep 2022
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No new features introduced.
15.5(1)SY8 – 16 Sep 2021
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No new features introduced.
15.5(1)SY6 – 18 Sep 2020
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Password hardening: Automatic conversion of older password types into stronger formats.
15.5(1)SY5 – 18 Mar 2020
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Software enhancements:
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Support for advanced password types (Type 6 and reversible Type 9).
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VRF-aware DHCP Option 82 with IANA settings support.
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15.5(1)SY4 – 12 Sep 2019
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Software enhancements:
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Deprecation of Type 4 password types and warnings for legacy passwords.
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Secure Field Programmable Gate Array (FPGA) support and updated auto-upgrade procedures.
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New NAT statistics command and support for NAT statistic MIB.
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Earlier Releases
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Supported PIM Join to IGMP Proxy (SY3).
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VPLS BGP Autodiscovery HA, interface template ACL support (SY2).
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SDA Phase 1.1 and L2 overlay features (SY1).
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Initial hardware additions such as C6800-8P40G, C6800-8P40G-XL (base SY).
Unsupported Features
The following feature sets are not supported in the 15.5SY train:
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MACsec Key Agreement Protocol (MKA)
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Smart Install
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Data Link Switching (DLSw)
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Serial Tunneling (STUN) and Bisync variants
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Airline Product Set (ALPS) features and other legacy tunneling/subsystem protocols.
Restrictions
Operational and configuration restrictions applicable across the 15.5SY train are documented per maintenance release and include legacy bridging, tunneling, and subsystem limitations.
Caveats
This section contains open and resolved issues for each revision of the 15.5SY train. Caveats are grouped by release and include detailed descriptions and conditions.
Troubleshooting
Troubleshooting guidance for the platform is provided, covering common failure scenarios and recommended recovery steps.
System Software Upgrade Instructions
Recommended procedures for preparing, staging, upgrading, and validating software images on supported hardware are described.
Additional Note
If required, please visit https://itmall.sale/.