ASN Use Cases and Real-World Examples: When You Need an Autonomous System Number

Understanding when and why organizations need an Autonomous System Number (ASN) is crucial for network infrastructure planning. While ASNs are fundamental to Internet routing, not every organization needs one. This article explores practical use cases, real-world examples, and decision criteria to help you determine if your organization should obtain an ASN.

Understanding ASN Use Cases

ASNs serve specific networking purposes that align with particular business and technical requirements. Let's explore the primary use cases where obtaining an ASN makes business and technical sense.

Use Case 1: Internet Service Providers (ISPs)

Internet Service Providers are the most common and obvious users of ASNs, as they form the backbone of Internet connectivity.

Why ISPs Need ASNs

Fundamental requirements:

• Announce their own IP address space to the Internet
• Establish peering relationships with other ISPs
• Implement independent routing policies
• Provide connectivity services to customers
• Participate in Internet exchange points

Technical benefits:

• Control over inbound and outbound traffic routing
• Ability to implement traffic engineering
• Independence from upstream provider routing decisions
• Capacity to establish multiple upstream connections (multi-homing)

Real-World ISP Examples

Regional ISP Example:

A regional ISP serving enterprise customers in Europe holds AS64500 (example). They:

• Announce their IPv4 /20 and IPv6 /32 allocations
• Maintain transit connections with two Tier-1 providers (AS174 Cogent and AS3356 Lumen)
• Peer at multiple Internet Exchange Points (AMS-IX, DE-CIX, LINX)
• Implement BGP communities for traffic engineering
• Provide BGP transit services to business customers

Major ISP ASN Examples:

• AT&T: AS7018 - One of the largest US telecommunications providers
• Verizon: AS701 - Major North American ISP and Tier-1 network
• Orange: AS5511 - Major European telecommunications provider
• Telefónica: AS12956 - Spanish multinational telecommunications company

According to IPinfo data, ISPs manage the vast majority of IP address allocations globally, with individual large ISPs managing millions of IP addresses across their ASNs.

When ISPs Need Multiple ASNs

Large ISPs often hold multiple ASNs for:

• Geographic separation: Different ASNs for different regions or countries
• Service differentiation: Separate ASNs for consumer vs. enterprise services
• Acquired companies: Maintaining ASNs from acquired businesses during integration
• Technical isolation: Separating different network architectures or technologies

Use Case 2: Hosting Providers and Data Centers

Hosting providers and data center operators commonly need ASNs to provide reliable, high-performance services to customers.

Why Hosting Providers Need ASNs

Business requirements:

• Assign IP addresses to customer servers and services
• Provide high-availability connectivity
• Offer BGP services to customers
• Maintain provider independence
• Establish peering relationships for cost optimization

Technical requirements:

• Multi-homed connectivity for redundancy
• Control over routing policies
• Ability to announce customer IP space
• Traffic engineering for optimal performance

Real-World Hosting Provider Examples

Cloud Hosting Provider Example:

A European cloud hosting provider (AS65100, example) operates data centers in Amsterdam, Frankfurt, and London. Their ASN enables:

• Announcing customer IPv4 /24 allocations and IPv6 /48 assignments
• Multi-homing through three different transit providers for 99.99% uptime
• Peering at local IXPs to reduce latency and costs
• Offering BGP services to enterprise customers
• Implementing anycast for distributed services

Major Hosting Provider ASN Examples:

• Amazon Web Services: AS16509 (primary) - AWS manages approximately 110 million IP addresses, roughly 3% of total IPv4 space according to industry analysis
• Google Cloud: AS15169 (primary) - Global cloud infrastructure
• Microsoft Azure: AS8075 (primary) - Major cloud services provider
• DigitalOcean: AS14061 - Cloud hosting focused on developers
• OVHcloud: AS16276 - European hosting and cloud provider

Specialized Hosting Use Cases

Anycast CDN Implementation:

A hosting provider implements anycast for DDoS protection:
- Same /24 IPv4 prefix announced from AS64500 in multiple locations
- Locations: Amsterdam (AMS-IX), Frankfurt (DE-CIX), Paris (France-IX)
- Traffic automatically routes to nearest PoP
- DDoS attacks distributed across multiple locations

Use Case 3: Enterprise Networks

Large enterprises increasingly obtain ASNs for mission-critical connectivity and network independence.

Why Enterprises Need ASNs

Business drivers:

• Business continuity requirements
• Provider independence
• Cost optimization through competitive sourcing
• Simplified provider migration
• Professional network infrastructure

Technical drivers:

• Multi-homed connectivity for high availability
• Control over failover behavior
• Traffic engineering based on business requirements
• Own IP addressing independent of providers

Real-World Enterprise Examples

Financial Services Company:

A multinational bank (AS64600, example) uses their ASN for:

• Connecting headquarters and trading floors to multiple ISPs
• Redundant connectivity for business-critical applications
• Provider-independent IPv4 /23 and IPv6 /48 allocations
• Precise control over inbound traffic routing
• Compliance with financial industry resilience requirements

Enterprise Multi-homing Configuration:

Enterprise Network: AS64600
Primary Transit: AS3356 (Lumen/Level3) - 1 Gbps
Secondary Transit: AS1299 (Telia) - 1 Gbps
IP Space: 203.0.113.0/23 (PI space)

BGP Configuration:
- Both providers receive full routing table
- Announce own prefixes with equal AS-PATH
- Use communities for traffic engineering
- Implement automatic failover

Enterprise Sectors Commonly Using ASNs:

• Financial services (banks, trading firms, insurance)
• Healthcare organizations (hospitals, medical networks)
• Technology companies with critical online services
• E-commerce platforms requiring high availability
• Government agencies with security requirements

When Enterprises DON'T Need ASNs

Many enterprises don't need ASNs because:

• Single ISP connection is sufficient for their needs
• Provider-managed redundancy is adequate
• Cost of obtaining and managing ASN outweighs benefits
• Lack of technical expertise to manage BGP routing
• Business criticality doesn't justify complexity

Use Case 4: Content Delivery Networks (CDNs)

CDNs use ASNs to implement global content distribution with optimal performance.

Why CDNs Need ASNs

Technical requirements:

• Anycast implementations for geographic load balancing
• Multiple Points of Presence (PoPs) worldwide
• Direct peering with ISPs and eyeball networks
• Control over traffic steering
• Low-latency content delivery

Business requirements:

• Global content distribution
• Performance optimization
• Cost-effective content delivery
• Direct relationships with ISPs
• Competitive differentiation

Real-World CDN Examples

Major CDN ASN Examples:

• Cloudflare: AS13335 - Global CDN and security provider with 300+ PoPs worldwide
• Akamai: AS20940 (and others) - One of the largest CDN providers globally
• Fastly: AS54113 - Edge cloud platform and CDN
• Cloudfront (Amazon): Uses various AWS ASNs including AS16509

CDN Anycast Implementation:

Cloudflare's AS13335 is an excellent example of anycast CDN architecture:

• Same IP prefixes announced from 300+ locations globally
• Traffic automatically routes to nearest PoP based on BGP routing
• DDoS mitigation through distributed infrastructure
• Sub-100ms latency for 95% of global Internet-connected population

Anycast Configuration Example

CDN Network: AS65200
Service IP: 203.0.113.0/24 (anycast prefix)

PoP Locations:
- New York: Announces 203.0.113.0/24 to AS3356, AS6939
- London: Announces 203.0.113.0/24 to AS1299, peering at LINX
- Tokyo: Announces 203.0.113.0/24 to AS2914, peering at JPIX
- Sydney: Announces 203.0.113.0/24 to AS4826, peering at Equinix Sydney

Result: Users automatically connect to geographically nearest PoP

Use Case 5: Internet Exchange Points (IXPs)

Internet Exchange Points are critical Internet infrastructure that enable direct interconnection between networks.

Why IXPs Have ASNs

Technical purposes:

• Operate route servers for IXP participants
• Manage IXP peering LAN addressing
• Facilitate multilateral peering
• Provide looking glass services
• Operate IXP infrastructure services

Operational purposes:

• Represent the IXP as a neutral entity
• Facilitate peering between members
• Provide technical services to participants
• Maintain IXP route server infrastructure

Real-World IXP Examples

Major IXP ASN Examples:

• AMS-IX (Amsterdam): AS1200 - One of the world's largest IXPs
• DE-CIX (Frankfurt): AS6695 - Europe's largest IXP by data transfer
• LINX (London): AS5459 - Major London Internet exchange
• Equinix (Multiple locations): AS24115 - Global IXP operator

IXP Route Server Function:

Most IXPs operate route servers that:

• Accept BGP sessions from IXP members
• Redistribute routes among participants
• Eliminate need for full-mesh BGP peering
• Filter invalid routes and provide security
• Simplify peering configuration for members

Use Case 6: Mobile Network Operators

Mobile carriers use ASNs for their data networks and mobile Internet services.

Why Mobile Operators Need ASNs

Network requirements:

• Announce mobile data network IP space
• Provide Internet connectivity to mobile subscribers
• Implement roaming interconnections
• Deliver mobile services (MMS, mobile apps, etc.)
• Optimize mobile data routing

Examples of Mobile Operator ASNs:

• Vodafone: AS1273 (and multiple regional ASNs)
• T-Mobile: AS21928 (US), various international ASNs
• Orange Mobile: Multiple ASNs across operating regions
• China Mobile: AS9808 - World's largest mobile operator

Mobile-Specific Considerations

Mobile operators often:

• Use Carrier-Grade NAT (CGN) for IPv4 subscribers
• Rapidly deploy IPv6 to mobile devices
• Implement complex routing for roaming traffic
• Use ASNs for both mobile data and fixed-line services

Use Case 7: Research and Education Networks

Universities, research institutions, and education networks use ASNs for academic connectivity.

Why Research Networks Need ASNs

Academic requirements:

• Connect to research networks (GÉANT, Internet2, etc.)
• Participate in academic peering
• Support research collaboration
• Provide campus-wide connectivity
• Enable international research partnerships

Examples of Research Network ASNs:

• GÉANT (European research network): AS20965
• Internet2 (US research network): AS11537
• CERN: AS513 - European particle physics laboratory
• JANET (UK education network): AS786

Research networks often receive preferential treatment in ASN application processes due to their contribution to Internet development and education.

Decision Framework: Do You Need an ASN?

You Probably NEED an ASN If:

1. You're an ISP providing Internet connectivity to customers
2. You require multi-homing with two or more upstream providers for business continuity
3. You operate a hosting service and need provider-independent addressing
4. You're implementing anycast for geographic load distribution
5. You need provider independence to maintain business flexibility
6. You participate in IXPs and establish peering relationships
7. Traffic engineering is critical for your business operations

You Probably DON'T Need an ASN If:

1. Single ISP connection meets your redundancy requirements
2. Provider-managed failover is sufficient for your needs
3. You lack BGP expertise and don't plan to develop it
4. Cost outweighs benefits for your use case
5. Small-scale operations don't justify the complexity
6. Testing or learning purposes (use private ASNs instead)

Cost-Benefit Considerations

Benefits of Having an ASN

Technical benefits:

• Full control over routing policies
• Provider independence and flexibility
• Improved redundancy and failover
• Traffic engineering capabilities
• Professional network infrastructure

Business benefits:

• Reduced provider switching costs
• Better negotiating position with ISPs
• Enhanced service reliability
• Professional credibility
• Competitive advantage in some markets

Costs of Having an ASN

Direct costs:

• RIR registration fees ($250-€1,400+ annually depending on RIR)
• Multiple transit connections ($1,000-$10,000+ monthly)
• BGP-capable routing equipment ($2,000-$50,000+)
• IP address allocations (if not already held)

Indirect costs:

• Staff training and expertise
• Ongoing management overhead
• Monitoring and maintenance
• Compliance with RIR policies

For detailed cost analysis, see our Cost Breakdown: ASN Registration Fees.

Getting Started with ASN Registration

If you've determined that your organization needs an ASN:

1. Assess your requirements - Confirm multi-homing or unique routing policy needs
2. Choose your RIR approach - Direct membership or sponsoring LIR
3. Gather documentation - Prepare technical justification and organizational documents
4. Secure upstream agreements - Establish relationships with ISPs before applying
5. Submit application - Follow RIR-specific application procedures
6. Implement BGP - Configure routing after ASN assignment

For comprehensive guidance, see our Complete Guide to ASN Registration.

Using Via-Registry Services

Via-Registry.com simplifies ASN registration and management:

Our services:

• ASN needs assessment and consultation
• Application preparation for all RIRs
• Sponsoring LIR services (RIPE region)
• Documentation development and justification
• Ongoing ASN and registry management
• Technical support for BGP implementation

Get started with our ASN Registration Service to determine if an ASN is right for your organization.

Frequently Asked Questions

Can a small company get an ASN?

Yes, organization size doesn't determine ASN eligibility. Small companies that meet technical requirements (such as multi-homing) can obtain ASNs. However, costs and complexity should be carefully considered against business needs.

Do I need an ASN for a private network?

No, if your network doesn't connect to the Internet or only uses internal BGP, you can use private ASNs (64,512-65,534 or 4,200,000,000-4,294,967,294). Private ASNs are free and don't require RIR registration.

Can I get an ASN just for learning BGP?

RIRs require demonstrated operational need for public ASNs. For learning purposes, use private ASNs in lab environments. Some RIRs or sponsoring LIRs may accommodate educational institutions with specific programs.

How do major companies like Google use their ASNs?

Large companies like Google (AS15169) use their ASNs to:

• Announce massive IP address blocks
• Implement global anycast networks
• Establish direct peering with thousands of networks
• Control traffic engineering across worldwide infrastructure
• Optimize content delivery and service performance

What happens if I get an ASN but don't use it?

Unused ASNs may be reclaimed by RIRs. You must maintain active use, pay annual fees, and comply with RIR policies. If you no longer need your ASN, you should return it to the RIR.

Summary

ASNs serve diverse use cases across Internet infrastructure:

• ISPs: Fundamental requirement for providing Internet services
• Hosting providers: Essential for redundancy and provider independence
• Enterprises: Critical for business continuity and high availability
• CDNs: Enables anycast and global content distribution
• IXPs: Facilitates neutral interconnection infrastructure
• Mobile operators: Required for mobile data network operations
• Research networks: Supports academic collaboration and connectivity

Key decision factors:

• Multi-homing requirements
• Provider independence needs
• Business criticality of connectivity
• Technical capability and resources
• Cost-benefit analysis
• Long-term network strategy

Understanding these use cases helps organizations make informed decisions about ASN acquisition and network architecture.

Next Steps

Determine if an ASN is right for your organization:

• Learn the basics: Read What is an ASN? How BGP Routing Works
• Understand requirements: Review ASN Registration Requirements by RIR
• Calculate costs: See Cost Breakdown: ASN Registration Fees
• Start registration: Follow our Complete Guide to ASN Registration
• Prepare application: Learn How to Prepare Your ASN Justification