I've changed my CDN - how do I get iTunes to draw from the new CDN instead of the old?

Could you post more details, please. You are talking about a podcast you've created yourself? If you've changed the URL of the feed iTunes will lose track of your podcast unless you follow the procedure detailed here:

http://www.wilmut.webspace.virginmedia.com/notes/podcast.html#move

The term 'DNS' is meaningless in this situation - it means 'Domain Name Server'.

If you have further questions about this please post your iTunes Store and feed URLs and do please give more details about what you have done.

If iTunes is not working from the URL I can't suggest anything: but is this in fact what is happening? Can you post the URL of your iTunes Store page.

Incidentally if the IP number associated with the domain name has changed it's going to take around 48 hours for it percolate round the world's DNS servers.

I would guess that though there might be a day or two's break, it will sort itself out. The iTunes Store will presumably be calling the files by the domain name, and the DNS server Apple is using will provide the IP number: this should correct itself but as I say it can take a couple of days.

Subscribers will be calling the files using their own ISP's DNS servers so these might be quicker or slower to update.

I have no idea exactly how the Store operates, but as far as subscribers are concerned Apple isn't involved. Once you've subscribed to a feed, your iTunes application uses your computer's internet facilities to call the media files, and it can only do that from the URLs contained in the feed. This URL then goes to your ISP's domain name servers (or whatever you might be using instead such as Open DNS if you go for that sort of thing) and is converted to IP numbers to connect to the media files. So if the wrong set of files is being called, it's because any one individual's DNS servers haven't caught up.

All that said, I don't know enough about server technology (we're way outside making podcasts here) to know whether when you change the IP number associated with a domain you have to take steps to make sure the information propagates. It sounds as if you know more about that than I do.

Looking up cdn.traintalk.tv in Network Utility produces this result:

; <<>> DiG 9.6-ESV-R4-P3 <<>> cdn.traintalk.tv a +multiline +nocomments +nocmd +noquestion +nostats +search

;; global options: +cmd

cdn.traintalk.tv. 282 IN CNAME cdn.vps.net.c.footprint.net.

cdn.vps.net.c.footprint.net. 217 IN A 8.27.4.254

cdn.vps.net.c.footprint.net. 217 IN A 8.254.72.126

cdn.vps.net.c.footprint.net. 217 IN A 192.221.115.254

That's using Virgin Media's DNS server; I don't know whether this tells you anything useful. Using traceroute I got

traceroute: Warning: cdn.traintalk.tv has multiple addresses; using 8.254.72.126

traceroute to cdn.vps.net.c.footprint.net (8.254.72.126), 64 hops max, 52 byte packets

and the usual dozen or so hops before it started giving me just asterisks. I got fed up with waiting for it after 24 hops. Ping was somewhat unsuccessful:

PING cdn.vps.net.c.footprint.net (8.27.4.254): 56 data bytes

Request timeout for icmp_seq 0

Request timeout for icmp_seq 1

Request timeout for icmp_seq 2

Request timeout for icmp_seq 3

Request timeout for icmp_seq 4

Request timeout for icmp_seq 5

Request timeout for icmp_seq 6

Request timeout for icmp_seq 7

Request timeout for icmp_seq 8

--- cdn.vps.net.c.footprint.net ping statistics ---

10 packets transmitted, 0 packets received, 100.0% packet loss

Make of that what you will 🙂