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Trying to sort this out with our Netscaler provider but they have issues finding the problem for this aswell so asking her to see if anyone have any input on where to start looking.

We have Netscaler as an SSL offload handling traffic into our IIS site running on http. After an security upgrade of Netscaler we are experiencing quite a lot of loading errors of css, js and images. They get cut of while loading. In Firefox I get no clear error but looking at what has been transferred I can see that only part of the file has been downloaded even if it's Status 200. Same with images that are partially loaded showing only the top of the image. In Chrome I get net::ERR_HTTP2_PROTOCOL_ERROR 200 but can't see any more details about it.

It only affects some of the files but it's always css, js or image files that get this error and most of the time it's the same files. So it fails to load some files but loads other of same type just fine. Reloading the page sometimes fix the problem only to occur again on some of the next loads.

Googling the Chrome error doesn't give much so does anyone have any clue on what to go next in trying to debug this error?

Update: This is the current settings for http2 netscaler http2 configuration

Update 2: The issue has now been resolved and apparently the Netscaler version 12 had some Http2 issues since they came out with a patched version (12.1) the day after the upgrade was applied to our Netscaler. Took a little bit too long for our Netscaler consultant to see that unfortuanately so the issued were affecting us for unnecessary period of two weeks. Accepting Jans answer since the last comment was to upgrade to latest version.

Hyzac
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1 Answers1

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Getting the obvious out of the way: - Are your browsers up-to-date?

First things to look at on the NetScaler:

  • Is IC (Integrated Caching) enabled? If so, try disabling it and try again?
  • How is the HTTP-protocol configured?
  • Hos is SSL configured.

It might be due to incorrect HTTP/2 settings:

  • System --> HTTP parameters: is HTTP/2 Server-Side enabled or not?
  • Try configuring a HTTP profile under System --> Profiles --> HTTP?

If you want, I can have a quick look along with you too troubleshoot this.

Kind regards, Jan

Jan
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  • Yes latest versions of Chrome (78.0.3904.70) and Firefox Developer (71.0b3). Unfortunately this Netscaler is a shared setup and only managable by our consultant. I will pass the information to check these settings to them. As I understand the upgrade that was made was from Citrix Netscaler to Citrix ADC but have no clue what that means – Hyzac Oct 25 '19 at 12:21
  • The frustrating part is to understand the problem. Like what causes the browser to stop downloading certain resources int the middle of the transfer? – Hyzac Oct 25 '19 at 12:23
  • I get it, no problem. Well, if it ain’t caching, it ha to be in the http-profile containing the http/2 settings. Buffers are used to collect and send data over the wire, it is probably going wrong somewhere in that part, which explains why you still get a part of the image. – Jan Oct 26 '19 at 14:23
  • You could advise them to upgrade the NetScaler to a later build (if it isn’t on the latest one) – Jan Oct 26 '19 at 14:25