Cross-ISP Access Analysis

Issue Description

Users accessing services across different ISPs experience performance issues.

Common Scenarios

Geographic Cross-ISP

• Northern users accessing Southern servers
• Western users accessing Eastern servers
• International cross-border access

Provider Cross-ISP

• China Mobile accessing China Telecom servers
• China Unicom accessing China Mobile servers
• Small ISP accessing major ISP servers

Performance Impact

Possible Causes

Peering Issues

• Limited peering between ISPs
• Congested peering points
• Peering disputes
• Suboptimal routing

Infrastructure

• Limited inter-ISP links
• Congested backbone
• Poor last-mile connectivity
• CDN coverage gaps

Routing

• Suboptimal routing paths
• Route flapping
• BGP issues
• Traffic engineering problems

Investigation Steps

1. Path Analysis

   • Run MTR tests
   • Identify peering points
   • Check hop-by-hop latency
   • Analyze routing path

2. Performance Analysis

   • Compare same-ISP vs cross-ISP
   • Check latency by ISP pair
   • Analyze packet loss
   • Review throughput

3. Infrastructure Review

   • Check CDN coverage
   • Review server locations
   • Analyze DNS resolution
   • Check load balancing

4. Pattern Analysis

   • Identify worst ISP pairs
   • Check time-based patterns
   • Correlate with events
   • Review trends

Resolution

Infrastructure Solutions

• Deploy multi-ISP CDN
• Use BGP anycast
• Implement multi-homing
• Add edge servers

Routing Solutions

• Work with ISPs on peering
• Optimize DNS resolution
• Implement traffic steering
• Use route optimization

Application Solutions

• Implement adaptive streaming
• Use connection pooling
• Enable compression
• Optimize protocols

Prevention

• Regular cross-ISP testing
• Monitor ISP performance
• Document issues
• Plan capacity accordingly