Suppose I'm a Tier 3 provider with my own autonomous system number and ip address range, who purchases a transit agreement with a single Tier 1 provider.

Is this agreement sufficient to send and receive data from all other users connected to the internet? Or are further agreements with providers further downstream again required?

  • 2
    That is usually part of the service-level agreement (SLA).
    – Zac67
    Jul 19, 2021 at 11:59

2 Answers 2


Yes. In fact an agreement with any tier provider is sufficient. The difference is reliability, bandwidth, and cost.

  • That's good to know. I was wondering whether most of these agreements only captured the "single step forwarding" aspect of routing or the entire end-to-end path. So these SLA's probably include provisions about the received traffic too.
    – 2080
    Jul 19, 2021 at 12:38


A tier 1 provider relies entirely on sending data (and routes for incoming data) to customers and peers, they have no upstream providers. That means if you rely on a single tier 1 for transit and they get into a peering dispute you will lose access to parts of the internet.

If you are going to single home you have a lower risk going with a large tier 2 provider who has multiple upstreams in addition to their own peering.

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