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Expressions for evaluating a DNS message and identifying its carrier protocol

September 27, 2025

Contributed by:

C S

You can evaluate DNS requests and responses by using expressions that begin with DNS.REQ and DNS.RES, respectively. You can also identify the transport layer protocol that is being used to send the DNS messages.

The following functions return the contents of a DNS query.

Function	Description
DNS.REQ.QUESTION.DOMAIN	Return the domain name (the value of the QNAME field) in the question section of the DNS query. The domain name is returned as a text string, which can be passed to EQ(), NE(), and any other functions that work with text.
DNS.REQ.QUESTION.TYPE	Return the query type (the value of the QTYPE field) in the DNS query. The field indicates the type of resource record (for example, A, NS, or CNAME) for which the name server is being queried. The returned value can be compared to one of the following values by using the EQ() and NE()functions: A, AAAA, NS, SRV, PTR, CNAME, SOA, MX, and ANY. Note: You can use only the EQ() and NE() functions with the TYPE function. Example: DNS.REQ.QUESTION.TYPE.EQ(MX)

Function

Description

DNS.REQ.QUESTION.DOMAIN

Return the domain name (the value of the QNAME field) in the question section of the DNS query. The domain name is returned as a text string, which can be passed to EQ(), NE(), and any other functions that work with text.

DNS.REQ.QUESTION.TYPE

Return the query type (the value of the QTYPE field) in the DNS query. The field indicates the type of resource record (for example, A, NS, or CNAME) for which the name server is being queried. The returned value can be compared to one of the following values by using the EQ() and NE()functions: A, AAAA, NS, SRV, PTR, CNAME, SOA, MX, and ANY. Note: You can use only the EQ() and NE() functions with the TYPE function. Example: DNS.REQ.QUESTION.TYPE.EQ(MX)

The following functions return the contents of a DNS response.

Function	Description
DNS.RES.HEADER.RCODE	Return the response code (the value of the RCODE field) in the header section of the DNS response. You can use only the EQ() and NE() functions with the RCODE function. Following are the possible values: NOERROR, FORMERR, SERVFAIL, NXDOMAIN, NOTIMP, and REFUSED.
DNS.RES.QUESTION.DOMAIN	Return the domain name (the value of the QNAME field) in the question section of the DNS response. The domain name is returned as a text string, which can be passed to EQ(), NE(), and any other functions that work with text.
DNS.RES.QUESTION.TYPE	Return the query type (the value of the QTYPE field) in the question section of the DNS response. The field indicates the type of resource record (for example, A, NS, or CNAME) that is contained in the response. The returned value can be compared to one of the following values by using the EQ()and NE() functions: A, AAAA, NS, SRV, PTR, CNAME, SOA, MX, and ANY. You can use only the EQ() and NE() functions with the TYPE function. Example: DNS.RES.QUESTION.TYPE.EQ(SOA)

The following functions return the transport layer protocol name.

Function	Description
DNS.REQ.TRANSPORT	Return the name of the transport layer protocol that was used to send the DNS query. Possible values returned are TCP and UDP. You can use only the EQ() and NE() functions with the TRANSPORT function. Example: DNS.REQ.TRANSPORT.EQ(TCP)
DNS.RES.TRANSPORT	Return the name of the transport layer protocol that was used for the DNS response. Possible values returned are TCP and UDP. You can use only the EQ() and NE() functions with the TRANSPORT function. Example: DNS.RES.TRANSPORT.EQ(TCP)

The following functions return the name of the matched location when the query contains or does not contain the DNS ECS option.

Function	Description
DNS.REQ.OPT.ECS.IP.MATCHES_LOCATION	Return the name of the matched location that was used in the query with the DNS ECS option. Example:(DNS.REQ.OPT.ECS.IP.MATCHES_LOCATION(“.CH…..”)
client.IP.SRC.MATCHES_LOCATION	Return the name of the matched location that was used in the query without the DNS ECS option. Example: (client.IP.SRC.MATCHES_LOCATION(“.CH…..”)
DNS.REQ.OPT.ECS.IP.MATCHES_LOCATION OR client.IP.SRC.MATCHES_LOCATION	Common expression to be used in the policy when the DNS traffic may or may not have ECS option in the query. Example: “(((DNS.REQ.OPT.ECS.IP.MATCHES_LOCATION(“.CH…..”).typecast_text_t) ALT (client.IP.SRC.MATCHES_LOCATION(“.CH…..”).typecast_text_t)).eq(“true”))”

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NetScaler Secure Deployment Guide

Expressions for evaluating a DNS message and identifying its carrier protocol

September 27, 2025

Contributed by:

C S

September 27, 2025

Contributed by:

C S

Expressions for evaluating a DNS message and identifying its carrier protocol

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