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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: [dnsop] DNS Anycast revisited (fwd)
PWG> Date: Tue, 3 May 2005 18:03:12 -0400 PWG> From: Patrick W. Gilmore PWG> NB [translation, "operational content"]: Akamai does not use any PWG> anycast for HTTP. I am not at all certain why Paul is telling us PWG> this is a bad idea, since we don't do it. Then again, we might in PWG> the future, I am not privy to every decision in the company. (No, PWG> that is not a "hint", I really do not think we will do anycast HTTP PWG> for content delivery, but I also really do not know everything we PWG> will do in the future.) One also should distinguish between TCP _to_ an anycasted address and TCP _from_ an anycasted address. The latter is trickier, as asymmetric routing increases the chances that the session will need to be transferred to another pod: ac LAX --> uc PHX uc PHX --> ac DFW This presses the question of synchronization (how do LAX and DFW know about each other?) and source-based routing. IMNSHO there's more overlap between these two topics than one might expect, too. When anycast gets _really_ interesting is when an anycasted client makes a request [from an anycasted address] to an anycasted server. The results resemble persistent BGP oscillation due to poor MED choices: ac LAX --> ac PHX ac PHX --> ac DFW ac DFW --> ac ORD ac ORD --> ac SJC ac SJC --> ac LAX I could see that happening with anycasted SMTP, but it would be less likely (although certainly not impossible) with HTTP. i.e., an HTTP client isn't as likely to be anycasted as an SMTP client. Far too much to cover in a noisy NANOG thread. :-( Hence the need to agree on just what "anycast" is before debating the merits. Eddy -- Everquick Internet - http://www.everquick.net/ A division of Brotsman & Dreger, Inc. - http://www.brotsman.com/ Bandwidth, consulting, e-commerce, hosting, and network building Phone: +1 785 865 5885 Lawrence and [inter]national Phone: +1 316 794 8922 Wichita ________________________________________________________________________ DO NOT send mail to the following addresses: [email protected] -*- [email protected] -*- [email protected] Sending mail to spambait addresses is a great way to get blocked. Ditto for broken OOO autoresponders and foolish AV software backscatter.
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