Peering Decisions on the Internet

Intro to peering decisions

To make better peering decisions, we need to analyze the peering components. Peering is as simple as two networks / providers agreeing to exchange traffic. Since the exchange is beneficial for both sides, it is most often done for free. Peering also reduces operating costs as it gets you free transit, instead of paid traffic. At the same time, peering improves the user experience of the visitors by:

• improving our routing decisions
• decreasing network latency

Public Peering

Public peering, the most used type of peering, happens through exchange points. Exchange point is a layer 2 network where other networks can:

• meet
• interconnect and
• exchange traffic

Usually, all members within one exchange point, share a common broadcast domain. Exchange points simplify peering decisions by giving its members the opportunity to talk, agree and, establish peering with each other. There are two types of public peering - bilateral & multilateral.

Bilateral peering

Besides mutual benefit, bilateral peering gets you control over your prefixes and announcement. Send out a request to peer and wait for a peer to reach back.

Multilateral peering

Multilateral peering gives you less control than bilateral. It's done by establishing sessions with each exchange point’s route servers. Route servers hold many prefixes, gathered from other peers. The number of accepted prefixes depends on ones route filters. Multilateral peering is simple to setup, but also not desirable for larger peers.

Private Peering

Private peering is a better option for large traffic volumes, with security and cost in mind. It is a direct inter-connection between two networks, like an dedicated circuit or fiber (dark fiber). Private peering is more cost-effective too, as the costs of maintaining mutual links are split. Yet, if one peer has too many private peering agreements with other peers, costs can increase.

Peering Policies

Why would someone want to peer with another network. There are three basic peering categories:

• Open
• Selective
• Restricted

Peers with an open policy are willing to peer with almost anyone. Selective peers have a set of rules and requirements, that only some peers can meet. Selective peering policies mean that one peer focuses on larger peers, while filtering out the small ones. Restrictive peering policies usually won’t accept any peer, as the bar is too high for most to reach it.

Conclusion

You should always try to find reliable peering partner with:

• enough locations to peer at
• enough PoP presence
• an adequate traffic volume to exchange to have a benefit

Peering often starts out easy but gets harder as you go. It isn’t free either. The more peers you have, the more capacity upgrades you need, and then more money goes for MCR to exchange points, or for dedicated transport or fiber links. By peering you become susceptible to bad routing policies and congestion in other peers’ networks too. But that’s how it is, it’s a double-edged sword, and it’s only a decision to peer or not to peer.