Here on the Packet Pushers podcast, we alternate between prognostication and practicality when it comes to networking. Today, we’ve got a thought-provoking design show about anycast TCP, a trip on the practical side of the galaxy.
Now, you might thinking, “Anycasting IP addresses that are used for TCP applications? Say it isn’t so. It simply can’t be done. All that statefulness! What if the network changes in-flight? Oh, the humanity!”
Indeed. I feel a great disruption in the network, as if millions of sessions timed out in terror and were suddenly terminated. Or was that merely a trip on the Hyperbole Falcon?
To help us sort out the realities of anycast TCP, we’ve got Zaid Ali Kahn, Director of Global Infrastructure Architecture and Strategy at LinkedIn, joining us.
We start with the basics of anycast, explore use cases, and then dig into the technical issues of anycast use in production.
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Section 1: The Basics: What Is Anycast?
- Defining anycast
- How do service providers use anycast?
- What are some anycast use cases for enterprises?
Section 2: Understand The Problem Of Anycast With TCP
Section 3: Anycast In Real Life
- How stable is a network, really?
- Even if the network changes, how often does the nearest anycast IP actually change?
- The problem as described is only an issue for long-lived TCP sessions, right?
- If a server dies, how quickly can I withdraw my anycast announcement?
- BGP only deals in /24 blocks or larger. Is this an issue with anycast, where we might be thinking in terms of a single IP?
- Latency vs. hop-count. A lower hop-count does not necessarily equal better performance
- Regional vs. global anycast
Section 4: Other Questions
- Can applications be engineered to better cope with an anycast environment?
- Does IPv6 introduce any new complications into anycast?
TCP Anycast: Don’t believe the FUD – NANOG presentation (PDF)
TCP over IP Anycast – Pipe dream or Reality? – LinkedIn Engineering blog