White paper

Traffic routing basics (BGP focus) 

Traffic routing basics

Download our white paper to learn more about inbound and outbound routing, how a router decides which path is best, localpref, MED and AS-PATH rules, and best practices.

Basic information

  • You define where packets leave your network
  • The other party defines which route is used to route the packets back to you
  • In most cases, the Internet is not routed symmetrically

Routing outbound

Routing packets from your network to the other network are defined by you.

  • Your router sends outgoing packets on the basis of its routing table
  • The routing table is built up based on learned (=incoming) prefixes from neighbors
  • Prefixes are typically learned from:
  1. Transit sessions
  2. Peering sessions (IXP or PNI)
  3. Customer sessions
  • If you have more than one router, your routers synchronize their learnings via IBGP

First, you have to learn a route from outside; then you can use it to send packets there.

  • In an advanced network, your router sees the prefixes from the target network on different paths
  • As there is more than one way of learning prefixes, you have to define where the outbound packet should be sent

Download the pdf to read more!

To learn more about traffic routing basics, please download the pdf. For customers, the pdf is available in the DE-CIX customer portal.

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