BGP Traffic Control: Outbound & Inbound Simplified

📝 Introduction:
Managing traffic in a multi-ISP network can get tricky.
Understanding how BGP attributes, prefix-length, communities, PBR, and QoS work together can help you control outbound traffic and influence inbound traffic efficiently.

1️⃣ Outbound Traffic Control (CE → Internet)
🔹 Local Preference (BGP Attribute) → Decide preferred exit path within your AS
Higher value → traffic prefers that ISP
🔹 PBR (Policy-Based Routing) → Steer specific traffic (e.g., VoIP) via preferred ISP
Packet-level control
🔹 QoS → Prioritize traffic based on type (VoIP, video)
Ensure latency-sensitive traffic gets high-priority treatment
💡 Rule: Outbound traffic is fully under your control.

2️⃣ Inbound Traffic Influence (Internet → CE)
🔹 Longest Prefix Match → More specific prefixes are preferred by the internet e.g., /24 preferred over /23.
🔹 AS-Path Prepending → Make a route less attractive by lengthening the AS path.
Influence ISP or remote AS routing decisions
🔹 BGP Communities (ISP-defined) → Ask ISP to adjust Local Preference on their side.
💡 Rule: Inbound traffic can only be influenced, not fully controlled.

4️⃣ Quick Concept Lock
Local-Pref = outbound route-level control
PBR = outbound path steering
QoS = outbound packet priority
AS-Path Prepending = inbound influence
Prefix-Length = inbound influence
BGP Communities = inbound ISP-side influence