Full English Description for Cisco PIX 520
1. Official Short Order Description (Datasheet Standard Format)
Cisco PIX 520: Early mid-range modular carrier-class 1U rack-mount stateful inspection firewall from the original PIX 500 series, positioned between vintage PIX 510 and higher-end PIX 525 chassis. Equipped with four empty PCI expansion slots for user-selectable 10/100 FE, Token Ring, FDDI or Private Link VPN accelerator cards, no fixed onboard Ethernet ports. Runs legacy PIX OS v4.x / v5.x only;PIX OS 7.x is unsupported. Built on Cisco Adaptive Security Algorithm (ASA), it delivers full stateful SPI firewall, IKEv1 IPsec site-to-site & remote access VPN, inline IDS intrusion detection, NAT/PAT, multi-zone DMZ segmentation, and hardware VPN offload via Private Link PCI cards. Performance scales up to 300 Mbps cleartext throughput, supporting 250,000 concurrent TCP/UDP connections and hundreds of simultaneous IPsec tunnels, unlimited internal host licensing with no user count caps. Managed via serial CLI, Syslog, SNMP v1/v2 and TFTP image backup; no native PDM web GUI support. Fully End-of-Sale and End-of-Support obsolete hardware, superseded by PIX 525 and later ASA 5500 series adaptive security appliances.
2. Complete Detailed Product Overview
Product Line Positioning
The Cisco PIX 520 is a first-generation modular rack-mount PIX firewall released before the PIX 515 platform, designed for medium enterprise, campus and small service provider edge deployments requiring flexible multi-media interface expansion. Unlike fixed-port desktop PIX-501/506 or two-slot PIX 515 series, the PIX 520 features four PCI slots to mix copper Ethernet, Token Ring, FDDI fiber backbone and dedicated VPN acceleration adapters to match complex multi-segment network topologies (inside, outside, multiple DMZs, campus fiber interconnections).
It shares the core stateful inspection ASA architecture with all PIX firewalls but carries strict early-generation OS limitations: it cannot boot PIX OS 6.x or 7.x, lacks embedded PDM graphical web management, and relies entirely on CLI/TFTP for configuration maintenance. The platform reached End-of-Sale in 2003 and End-of-Support in 2010; no official firmware updates, bug fixes or Cisco technical support exist today, only encountered in legacy network lab training environments.
Physical Hardware & Modular PCI Architecture
Form Factor & Mechanical Specifications
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Standard 1U 19-inch rack-mount metal chassis, front panel multi-color LED indicators for power, system fault and per-interface link activity
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Single internal universal AC power supply (100–240V AC) with variable-speed cooling fan; optional external 48V DC power feed SKUs for telecom central office deployments
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Integrated physical security lock slot for anti-tampering protection
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Fixed non-upgradeable hardware core: Single x86 processor, base 16 MB SDRAM (field-upgradeable to 128 MB), minimum 2 MB flash memory card for PIX OS and persistent configurations
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Four empty 32-bit PCI expansion slots (primary differentiator vs PIX 510/515 with fewer PCI slots)
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No factory-built onboard Ethernet ports; all LAN/WAN/DMZ interfaces are field-installed via PCI adapters
Supported PCI Modular Interface Cards
Administrators populate PCI slots to build custom multi-segment network topologies:
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PIX-1FE: Single-port 10/100 Fast Ethernet RJ45 card
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PIX-4FE: Four-port auto-sensing 10/100 Fast Ethernet RJ45 card
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Token Ring PCI adapters for legacy IBM campus network integration
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PIX-FDDI: Single-port FDDI fiber interface card for high-speed campus backbone interconnection
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Private Link VPN accelerator PCI card for hardware IPsec encryption offload
Maximum functional limit: Up to six usable Layer 3 logical interfaces; extra PCI ports beyond six are recognized but cannot be assigned routed security zones.
Rear Panel Fixed Ports
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RJ45 RS-232 Serial Console Port: Out-of-band CLI management at default 9600 baud for initial bootstrap, password recovery and offline config editing
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IEC AC power input socket for internal power supply
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Four horizontal PCI expansion slot bays for field-installed network/VPN adapters
Core Performance & Licensing Limits
Throughput & Session Capacity Benchmarks
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Maximum cleartext stateful firewall throughput: Up to 300 Mbps
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Maximum concurrent TCP/UDP connection table entries: 250,000
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Software-only IPsec VPN throughput: DES up to 22 Mbps, 3DES up to 12 Mbps
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IPsec VPN throughput with Private Link PCI accelerator card: Up to 70 Mbps 3DES
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Maximum simultaneous IKEv1 IPsec security associations (site-to-site + remote access): 300 concurrent tunnels
Host Licensing
No restrictive active internal host count license; unlimited LAN endpoint support with no paid user upgrade keys, eliminating the 10/50 host limitations seen on entry PIX-501 hardware.
Full Integrated Security & Networking Feature Suite (PIX OS v4.x / v5.x Only)
1. Stateful Inspection Firewall (Cisco Adaptive Security Algorithm)
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Full stateful packet inspection tracking all TCP/UDP connection states to block invalid stateless traffic
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Static and dynamic access control lists (ACLs) for granular inbound/outbound traffic filtering
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Basic multi-vector DoS/DDoS flood mitigation, port scan detection and malformed packet filtering
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Early Layer 7 "fixup protocol" inspection engines for FTP, H.323, SIP, RTSP, NetBIOS to preserve NAT traversal for VoIP and multimedia workloads
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No transparent Layer 2 firewall mode (transparent mode introduced in later PIX OS 7.x unsupported on PIX 520)
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Third-party URL web content filtering integration for outbound internet access control
2. Standards-Based IPsec VPN Suite
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Site-to-site LAN-to-LAN IPsec tunnels for secure inter-branch private connectivity over public internet
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Remote access IPsec VPN for legacy Cisco VPN Client teleworker tunnels back to corporate headquarters
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IKEv1 key exchange protocol only, compatible with DES, 3DES encryption and MD5/SHA-1 authentication
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X.509 digital certificate enrollment via SCEP for scalable multi-site VPN deployments
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GRE tunnel encapsulation for routed non-IPsec traffic across VPN links
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Optional Private Link PCI accelerator card to offload crypto processing and boost VPN throughput
3. NAT & Broadband Networking Services
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Static one-to-one NAT, dynamic NAT pools, PAT port address translation to share a single public IP across hundreds of internal devices
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Static routing and policy-based routing (PBR); IPv4-only native support (no native IPv6 protocol stack on PIX OS v4/v5)
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Local DHCP server for internal LAN IP address allocation
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No native PPPoE client (PPPoE broadband authentication added in PIX OS 6.x for later PIX 506/515 series)
4. Intrusion Detection & Threat Defense
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Built-in inline IDS engine with predefined attack signatures to detect worms, exploits and brute-force network scanning
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Automatic dynamic host blocking to quarantine malicious source IP addresses after detected security events
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Unicast Reverse Path Forwarding (URPF) strict/loose anti-spoof filtering to block forged source IP packets
5. AAA Access Control & Audit Logging
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Complete AAA authentication, authorization and accounting via external RADIUS and TACACS+ servers
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Local user credential database for standalone device administrative login
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Persistent local event logging + remote Syslog export to external log servers for compliance audit trails
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SNMP v1/v2 monitoring for device health, traffic utilization and fault alert reporting
Management & Configuration Tools
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PIX CLI Console: Primary Cisco IOS-style command-line interface via serial console or SSH remote access; no embedded web GUI (PDM web manager unsupported on PIX 520)
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TFTP Server: Exclusive method for OS firmware and full configuration backup/restore, no USB storage support
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Cisco Secure Policy Manager (CSPM): Centralized enterprise policy management platform for bulk multi-PIX deployment orchestration
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No ASDM graphical management capability, a critical limitation compared to later PIX 515/515E hardware
Key Differentiators vs Related PIX Models
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vs PIX 510: Four PCI slots (two slots on PIX 510), higher 300 Mbps cleartext throughput, larger 250,000 concurrent connection table, higher maximum VPN tunnel capacity
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vs PIX 515 / 515E: Older generation hardware, limited to PIX OS v4/v5.x only (cannot run OS 6.x / 7.x), no onboard fixed Fast Ethernet ports, no PDM web GUI support, smaller flash memory footprint, slower CPU architecture
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vs PIX-501 / 506 / 506E: Modular rack-mount chassis with expandable four PCI interface slots, unlimited host licensing, far higher concurrent session and VPN tunnel capacity, multi-DMZ multi-media segmentation support
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vs PIX 525: Lower throughput ceiling, smaller memory footprint, fewer native enterprise advanced features, lacks redundant power supply options standard on high-end PIX 525 chassis
Typical Historical Deployment Scenarios
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Medium enterprise campus edge firewall requiring mixed copper Ethernet, FDDI fiber and Token Ring multi-segment connectivity via modular PCI cards
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Early multi-site enterprise IPsec VPN hub aggregating hundreds of remote branch tunnels
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Small service provider colocation multi-tenant boundary security gateway for legacy mixed-media network environments
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Vintage network lab training platform for studying early PIX OS v4/v5 stateful firewall and modular PCI architecture
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Rural remote PoP multi-segment security gateway combining WAN, DMZ and internal campus LAN interfaces
3. E-commerce Short Marketing Description
Cisco PIX 520 Legacy Modular 1U Rack-Mount Stateful Inspection Firewall, original first-generation PIX series hardware with four empty PCI expansion slots for configurable Fast Ethernet, Token Ring, FDDI or Private Link VPN accelerator cards, running PIX OS v4.x / v5.x (OS 6.x/7.x unsupported). Delivers unlimited internal host licensing, stateful SPI firewall, IPsec IKEv1 site-to-site/remote access VPN, basic inline IDS intrusion detection, NAT/PAT and AAA authentication. Up to 300 Mbps cleartext throughput, 250,000 concurrent TCP/UDP sessions and 300 simultaneous IPsec VPN tunnels, managed exclusively via serial CLI and TFTP (no embedded web GUI). Fully obsolete end-of-support modular enterprise/campus firewall, predecessor to the PIX 525 high-end platform.
4. Product Catalog Keyword Tags
Cisco, PIX 520, PIX 500 Series Modular Legacy Firewall, Early-Generation Service Provider/Enterprise Security Appliance, 1U 19-inch Rack-Mount Chassis, Four Empty PCI Expansion Slots, Modular FE / Token Ring / FDDI / Private Link VPN Accelerator Cards, Single Internal AC / Optional 48V DC Power Supply, Cisco Adaptive Security Algorithm ASA, PIX OS v4.x v5.x Firmware Only (No OS 6.x/7.x Support), Stateful Packet Inspection SPI, IPsec IKEv1 Site-to-Site & Remote Access VPN, DES/3DES Encryption, Optional Private Link Hardware VPN Acceleration, Basic Inline IDS Intrusion Detection System, NAT PAT Static Dynamic Address Translation, AAA RADIUS TACACS+ Authentication, CLI-Only Management (No PDM Web GUI), TFTP Firmware & Config Backup, Syslog SNMP v1/v2 Monitoring, 300 Mbps Max Cleartext Firewall Throughput, 250,000 Concurrent TCP/UDP Connections, 300 Max Simultaneous IPsec VPN Tunnels, Unlimited Internal Host License, End-of-Sale End-of-Support Obsolete Hardware, Predecessor to PIX 525 High-End Chassis, Mixed-Media Campus Edge Firewall, Vintage Network Training Lab Platform
Naming Rule Explanation
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PIX: Private Internet Exchange, Cisco legacy dedicated firewall product family, fully replaced by the ASA Adaptive Security Appliance line
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520: Mid-range modular rack-mount model number from the original first-generation PIX hardware lineup
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Critical Distinction: The PIX 520 is an early vintage modular platform with four PCI expansion slots and limited OS compatibility, lacking graphical web management and modern PIX OS 6/7 features; it is completely separate from the later PIX 515/515E and PIX 525 generations which introduced onboard fixed Ethernet ports, PDM GUI and expanded firmware support. It has no active Cisco technical support or official firmware updates available today.
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