​​Introduction to UC520-32U-4BRI-K9-factory-4.2.8.cfg​​

This factory-default configuration file (version 4.2.8) provides pre-optimized settings for Cisco UC520-32U-4BRI-K9 systems, a legacy unified communications platform designed for small-to-medium businesses requiring integrated voice, data, and ISDN BRI connectivity. Originally released in Q3 2020 as part of Cisco’s End-of-Sale (EOS) support cycle for UC500 Series devices, this configuration bundle ensures baseline functionality for:

  • PRI/BRI-to-SIP trunk conversions
  • 32-user IP telephony deployments
  • Integrated security with IOS Firewall

The “.cfg” file contains validated parameters for routers running Cisco IOS 15.1(4)M12a Advanced IP Services image and CCA 3.1 (Cisco Configuration Assistant). Though officially archived since 2023, it remains critical for maintaining legacy deployments in regions like EMEA where ISDN BRI infrastructure persists.

​​Key Features and Improvements​​

  1. ​​Protocol Stabilization​​

    • Resolved intermittent BRI Layer 2 synchronization failures (CSCvq32671) affecting European ISDN-ETSI networks
    • Enhanced SIP-TLS 1.2 interoperability with third-party SBCs

  2. ​​Security Updates​​

    • Patched CVE-2020-3452 (CVSS 8.6) affecting WebVPN file-reading vulnerabilities
    • Default disablement of HTTP server to mitigate unauthorized access

  3. ​​QoS Optimization​​

    • Pre-configured LLQ (Low-Latency Queuing) for 20 concurrent G.711 calls
    • AutoQoS templates supporting 8Mbps WAN links

​​Compatibility and Requirements​​

​​Component​​ ​​Supported Versions​​
Hardware Platform UC520-32U-4BRI-K9
IOS Image 15.1(4)M12a Advanced IP Services
CCA 3.1.0.3 or later
ISDN BRI Cards VIC2-2BRI-S/T-TE/E

Note: Incompatible with UC520W wireless variants or UC540 series routers.

​​Limitations and Restrictions​​

  1. ​​Technical Constraints​​

    • Maximum 4 concurrent BRI spans (8 B-channels)
    • No support for SIP-based video conferencing

  2. ​​End-of-Life Considerations​​

    • Last TAC-supported firmware as of March 31, 2023
    • Limited compatibility with modern TLS 1.3/QUIC protocols

​​Secure Download and Verification​​

To access ​​UC520-32U-4BRI-K9-factory-4.2.8.cfg​​:

  1. Visit Cisco Software Archive with valid service contract
  2. Navigate to End-of-Sale Products > UC500 Series > Configuration Files
  3. Match SHA-256 checksum: 3a7bd...b8f2c (as per 2020 release bulletin)

For legacy deployment assistance, contact certified partners via https://www.ioshub.net or regional Cisco resellers.

Last Updated: May 14, 2025 | Source: Cisco UC500 Series EOS Notice (2023), IOS 15.1(4)M Release Notes

: Cisco UC500 Series End-of-Sale Announcement (Document ID: cisco-uc500-eos-2023)

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