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https://issues.apache.org/jira/browse/TS-4468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15296480#comment-15296480
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Susan Hinrichs commented on TS-4468:
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Did some research on this. The setting of SNI name for connections to origins
was added in 5.1. It uses the HOST header of the server request for the SNI
name for the connection from ATS to origin.
Some other fixing options include:
* Add option to not set SNI name.
* Add another option on server session reuse to match on SNI name (instead
of/in addition to FQDN and IP).
> http.server_session_sharing.match = both unsafe with HTTPS
> ----------------------------------------------------------
>
> Key: TS-4468
> URL: https://issues.apache.org/jira/browse/TS-4468
> Project: Traffic Server
> Issue Type: Bug
> Components: HTTP, SSL
> Affects Versions: 6.1.1
> Reporter: Jered Floyd
> Fix For: 7.0.0
>
>
> proxy.config.http.server_session_sharing.match has a default value of "both",
> which compares IP address, port, and FQDN when determining whether a
> connection can be reused for further user agent requests.
> The "host" (FQDN) matching does not behave safely when ATS is operating as a
> reverse proxy. The compared value is the origin server FQDN after mapping,
> rather than the initial "Host" target.
> If multiple Hosts map to the same origin server and the scheme is HTTPS, ATS
> will attempt to reuse a connection that may have an SNI Host that does not
> match the HTTP Host. With Apache 2.4 origin servers this results in 400 Bad
> Request to the user agent.
> PROBLEM REPRODUCTION:
> You can observe this behavior with two mapping rules such as:
> map https://example.com/ https://origin.example.com/
> map https://www.example.com/ https://origin.example.com/
> Non-caching clients alternately fetching URIs from the two targets will see
> 400 Bad Request responses intermittently.
> WORKAROUND:
> proxy.config.http.server_session_sharing.match should have a default value of
> "none" when proxy.config.reverse_proxy.enabled is "1"
> SUGGESTED FIXES:
> In order of completeness:
> 1) Do not share server sessions on reverse_proxy requests.
> 2) Do not share server sessions on reverse_proxy requests where scheme is
> HTTPS.
> 3) Compare target host (SNI host) rather than replacement host when
> determining if reuse of server session is allowed (when
> server_session_sharing.match is set to "host" or "both").
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