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.

Here is a preview:

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

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