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Glossary · concept

What is CDN (Content Delivery Network)?

A CDN (Content Delivery Network) is a globally distributed network of servers that caches content close to viewers, reducing latency and offloading traffic from origin servers. YouTube uses googlevideo.com as its video CDN — every video byte you watch comes from a googlevideo edge server geographically near you.

Also called:edge server · content delivery network · googlevideo

When you watch a YouTube video, the player isn't fetching bytes from "YouTube's servers" abstractly. It's fetching from a specific edge server in a specific datacenter that's physically close to your ISP's peering point. The URL hostname looks like rr3---sn-gxuo03g-3c2s.googlevideo.com — the rr3 is the route, the sn-... is a specific edge node identifier.

For downloaders, CDN behavior matters in a few ways. First, the IP that fetches the bytes affects which edge you get. Second, signed URLs are usually pinned to the IP that requested them (see the [signed URL glossary entry](/glossary/signed-url)) — fetching from a different IP returns 403. Third, ranges of CDN bandwidth vary by region — some edges throttle aggressively, others don't.

When you see "1080p downloads from YouTube faster than 1080p playback" — that's the CDN's parallel-range-request behavior at work. The player uses one TCP connection (capped at playback bitrate); a downloader opens 6 parallel range requests and saturates the available bandwidth.

Common questions

Why does the YouTube video URL hostname change?
CDN routing. Each video session is routed to the edge server best positioned for your IP at that moment. The hostname encodes which edge node was picked. Two viewers in different cities watching the same video usually get different hostnames.
Can I pick which CDN edge to use?
No — YouTube's routing layer picks for you based on your IP geolocation. The only way to "pick" a different edge is to change your IP (VPN, proxy). Even then, the edge is determined automatically based on the new IP.

Related terms

Signed URL

A signed URL is a download link with cryptographic parameters that authenticate the request and expire after a set time.

Range request (HTTP byte range)

A range request is an HTTP request that asks for a specific byte range of a file rather than the full thing.

IP fingerprinting

IP fingerprinting is the practice of evaluating an IP address against its history, ASN, country, type (residential vs datacenter), and behavioral patterns to decide how to treat requests.

VidPickr is a free, browser-based YouTube downloader. Every term in this glossary either describes how YouTube delivers video or why your downloads behave the way they do. Try the downloader →