sni.yaml

Description

This file is used to configure aspects of TLS connection handling for both inbound and outbound connections. With the exception of host_sni_policy (see the description below), the configuration is driven by the SNI values provided by the inbound connection. The file consists of a set of configuration items, each identified by an SNI value (fqdn). When an inbound TLS connection is made, the SNI value from the TLS negotiation is matched against the items specified by this file and if there is a match, the values specified in that item override the defaults. This is done during the inbound connection processing; some outbound properties can be overridden again later, such as via remap.config or plugins.

By default this is named sni.yaml. The filename can be changed by setting proxy.config.ssl.servername.filename. This file is loaded on start up and by traffic_ctl config reload if the file has been modified since process start.

The configuration file is YAML-based. After parsing the configuration, a list of tables will be the result. Each table is a set of key / value pairs that create a configuration item. This configuration file accepts wildcard entries. To apply an SNI based setting on all the server names with a common upper level domain name, the user needs to enter the fqdn in the configuration with a *. followed by the common domain name. (*.yahoo.com for example).

For some settings, there is no guarantee that they will be applied to a connection under certain conditions. An established TLS connection may be reused for another server name if it’s used for HTTP/2. This also means that settings for server name A may affects requests for server name B as well. See https://daniel.haxx.se/blog/2016/08/18/http2-connection-coalescing/ for a more detailed description of HTTP/2 connection coalescing.

Key	Direction	Meaning
fqdn	Both	Fully Qualified Domain Name. This item is used if the SNI value matches this.
ip_allow	Inbound	Specify a list of client IP address, subnets, or ranges what are allowed to complete the connection. This list is comma separated. IPv4 and IPv6 addresses can be specified. Here is an example list: 192.168.1.0/24,192.168.10.1-4. This would allow connections from clients in the 19.168.1.0 network or in the range from 192.168.10.1 to 192.168.1.4.
verify_server_policy	Outbound	One of the values DISABLED, PERMISSIVE, or ENFORCED. By default this is proxy.config.ssl.client.verify.server.policy. This controls how Traffic Server evaluated the origin certificate.
verify_server_properties	Outbound	One of the values NONE, SIGNATURE, NAME, and ALL By default this is proxy.config.ssl.client.verify.server.properties. This controls what Traffic Server checks when evaluating the origin certificate.
verify_client	Outbound	One of the values NONE, MODERATE, or STRICT. If NONE is specified, Traffic Server requests no certificate. If MODERATE is specified Traffic Server will verify a certificate that is presented by the client, but it will not fail the TLS handshake if no certificate is presented. If STRICT is specified the client must present a certificate during the TLS handshake. By default this is proxy.config.ssl.client.certification_level.
verify_client_ca_certs	Both	Specifies an alternate set of certificate authority certs to use to verify the client cert. The value must be either a file path, or a nested set of key / value pairs. If the value is a file path, it must specify a file containing the CA certs. Otherwise, there should be up to two nested pairs. The possible keys are file and dir. The value for file must be a file path for a file containing CA certs. The value for dir must be a file path for an OpenSSL X509 hashed directory containing CA certs. If a given file path does not being with / , it must be relative to the Traffic Server configuration directory. verify_client_ca_certs can only be used with capbilities provided by OpenSSL 1.0.2 or later.
host_sni_policy	Inbound	One of the values DISABLED, PERMISSIVE, or ENFORCED. If not specified, the value of proxy.config.http.host_sni_policy is used. This controls how policy impacting mismatches between host header and SNI values are dealt with. For details about hos this configuration behaves, see the corresponding proxy.config.http.host_sni_policy records.config documentation. Note that this particular configuration will be inspected at the time the HTTP Host header field is processed. Further, this policy check will be keyed off of the Host header field value rather than the SNI in this sni.yaml file. This is done because the Host header field is ultimately the resource that will be retrieved from the origin and the administrator will intend to guard this resource rather than the SNI, which a malicious user may alter to some other server value whose policies are more lenient than the host he is trying to access.
valid_tls_versions_in	Inbound	This specifies the list of TLS protocols that will be offered to user agents during the TLS negotiation. This replaces the global settings in proxy.config.ssl.TLSv1, proxy.config.ssl.TLSv1_1, proxy.config.ssl.TLSv1_2, and proxy.config.ssl.TLSv1_3. The potential values are TLSv1, TLSv1_1, TLSv1_2, and TLSv1_3. You must list all protocols that Traffic Server should offer to the client when using this key. This key is only valid for OpenSSL 1.1.0 and later and BoringSSL. Older versions of OpenSSL do not provide a hook early enough to update the SSL object. It is a syntax error for Traffic Server built against earlier versions.
client_cert	Outbound	The file containing the client certificate to use for the outbound connection. If this is relative, it is relative to the path in proxy.config.ssl.client.cert.path. If not set proxy.config.ssl.client.cert.filename is used.
client_key	Outbound	The file containing the client private key that corresponds to the certificate for the outbound connection. If this is relative, it is relative to the path in proxy.config.ssl.client.private_key.path. If not set, Traffic Server tries to use a private key in client_cert. Otherwise, proxy.config.ssl.client.private_key.filename is used.
client_sni_policy	Outbound	Policy of SNI on outbound connection. If not specified, the value of proxy.config.ssl.client.sni_policy is used.
http2	Inbound	Indicates whether the H2 protocol should be added to or removed from the protocol negotiation list. The valid values are on or off.
http2_buffer_water_mark	Inbound	Specifies the high water mark for all HTTP/2 frames on an outoging connection. By default this is proxy.config.http2.default_buffer_water_mark. NOTE: Connection coalescing may prevent this taking effect.
disable_h2	Inbound	Deprecated for the more general h2 setting. Setting disable_h2 to true is the same as setting http2 to on.
tunnel_route	Inbound	Destination as an FQDN and port, separated by a colon :. Match group number can be specified by $N where N should refer to a specified group in the FQDN, tunnel_route: $1.domain. This will forward all traffic to the specified destination without first terminating the incoming TLS connection.
forward_route	Inbound	Destination as an FQDN and port, separated by a colon :. This is similar to tunnel_route, but it terminates the TLS connection and forwards the decrypted traffic. Traffic Server will not interpret the decrypted data, so the contents do not need to be HTTP.
partial_blind_route	Inbound	Destination as an FQDN and port, separated by a colon :. This is similar to forward_route in that Traffic Server terminates the incoming TLS connection. In addition partial_blind_route creates a new TLS connection to the specified origin. It does not interpret the decrypted data before passing it to the origin TLS connection, so the contents do not need to be HTTP.
tunnel_alpn	Inbound	List of ALPN Protocol Ids for Partial Blind Tunnel. ATS negotiates application protocol with the client on behalf of the origin server. This only works with partial_blind_route.

Pre-warming TLS Tunnel

Key	Meaning
tunnel_prewarm	Override proxy.config.tunnel.prewarm in records.config.
tunnel_prewarm_srv	Enable SRV record lookup on pre-warming. Default is false.
tunnel_prewarm_rate	Rate of how many connections to pre-warm. Default is 1.0.
tunnel_prewarm_min	Minimum number of pre-warming queue size (per thread). Default is 0.
tunnel_prewarm_max	Maximum number of pre-warming queue size (per thread). Default is -1 (unlimited).
tunnel_prewarm_connect_timeout	Timeout for TCP/TLS handshake (in seconds).
tunnel_prewarm_inactive_timeout	Inactive timeout for connections in the pool (in seconds).

Client verification, via verify_client, corresponds to setting proxy.config.ssl.client.certification_level for this connection as noted below.

NONE – 0

Do not request a client certificate, ignore it if one is provided.

MODERATE - 1

Request a client certificate and do verification if one is provided. The connection is denied if the verification of the client provided certificate fails.

STRICT - 2

Request a client certificate and require one to be provided and verified. If the verification fails the failure is logged to diags.log and the connection is denied.

Upstream (server) verification, via verify_server_policy and verify_server_properties, is similar to client verification except there is always an upstream certificate. This is equivalent to setting proxy.config.ssl.client.verify.server.policy and proxy.config.ssl.client.verify.server.properties for this connection.

verify_server_policy specifies how Traffic Server will enforce the server certificate verification.

DISABLED

Do not verify the upstream server certificate.

PERMISSIVE

Do verification of the upstream certificate but do not enforce. If the verification fails the failure is logged in diags.log but the connection is allowed.

ENFORCED

Do verification of the upstream certificate. If verification fails, the failure is logged in diags.log and the connection is denied.

In addition verify_server_properties specifies what Traffic Server will check when performing the verification.

NONE

Do not check anything in the standard Traffic Server verification routine. Rely entirely on the TS_SSL_VERIFY_SERVER_HOOK for evaluating the origin’s certificate.

SIGNATURE

Check the signature of the origin certificate.

NAME

Verify that the SNI is in the origin certificate.

ALL

Verify both the signature and the SNI in the origin certificate.

If tunnel_route is specified, none of the certificate verification will be done because the TLS negotiation will be tunneled to the upstream target, making those values irrelevant for that configuration item. This option is explained in more detail in SNI Routing.

Examples

Disable HTTP/2 for no-http2.example.com.

sni:
- fqdn: no-http2.example.com
  http2: off

Require client certificate verification for foo.com and any server name ending with .yahoo.com. Therefore, client request for a server name ending with yahoo.com (e.g., def.yahoo.com, abc.yahoo.com etc.) will cause Traffic Server require and verify the client certificate.

For foo.com, if the user agent sets the host header to foo.com but the SNI to some other value, Traffic Server will warn about the mismatch but continue to process the request. Mismatches for the other domains will cause Traffic Server to warn and return 403.

Traffic Server will allow a client certificate to be provided for example.com and if it is, Traffic Server will require the certificate to be valid.

sni:
- fqdn: example.com
  verify_client: MODERATE
- fqdn: 'foo.com'
  verify_client: STRICT
  host_sni_policy: PERMISSIVE
- fqdn: '*.yahoo.com'
  verify_client: STRICT

Disable outbound server certificate verification for trusted.example.com and require a valid client certificate.

sni:
- fqdn: trusted.example.com
  verify_server_policy: DISABLED
  verify_client: STRICT

Use FQDN captured group to match in tunnel_route.

sni:
- fqdn: '*.foo.com'
  tunnel_route: '$1.myfoo'
- fqdn: '*.bar.*.com'
  tunnel_route: '$2.some.$1.yahoo'

FQDN some.foo.com will match and the captured string will be replaced in the tunnel_route which will end up being some.myfoo. Second part is using multiple groups, having bob.bar.example.com as FQDN, tunnel_route will end up being bar.some.bob.yahoo.

See Also

SNI Routing