dsc.conf(5)

NAME
dsc.conf - Configuration for the DNS Statistics Collector

DESCRIPTION
The file dsc.conf contains defaults for the program dsc(1) . Each line is a configuration option and may have arguments in the form option value;. Comment lines must have a hash sign (#) in the first column. Since dsc(1) version 2.2.0, a configuration line may not be divided with CR/LF and quoted characters are not understood (\quote).

CONFIGURATION

local_address IP [ MASK / BITS ] ;
    Specifies the DNS server's local IP address with an optional mask/bits for local networks. It is used to determine the direction of an IP packet: sending, receiving, or other. You may specify multiple local addresses by repeating the local_address line any number of times.

run_dir PATH ;
    A directory that will become dsc current directory after it starts. Output files will be written here, as will any core dumps.

minfree_bytes BYTES ;
    If the filesystem where dsc writes its output files does not have at least this much free space, then dsc will not write the files. This prevents dsc from filling up the filesystem. The files that would have been written are simply lost and cannot be recovered. Output files will be written again when the filesystem has the necessary free space.

pid_file " FILE " ;
    The file where dsc will store its process id.

bpf_program " RULE " ;
    A Berkeley Packet Filter program string. You may use this to further restrict the traffic seen but note that dsc currently has one indexer that looks at all IP packets. If you specify something like udp port 53 that indexer will not work. However, if you want to monitor multiple DNS servers with separate dsc instances on one collector box, then you may need to use bpf_program to make sure that each dsc process sees only the traffic it should see. Note that this directive must go before the interface directive because dsc makes only one pass through the configuration file and the BPF filter is set when the interface is initialized.

dns_port NUMBER ;
    dsc will only parse traffic coming to or leaving the DNS port (default 53), this option lets you control which port that is in case it's not standard.

pcap_buffer_size NUMBER ;
    Set the buffer size (in bytes) for pcap, increasing this may help if you see dropped packets by the kernel but increasing it too much may have other side effects. Note that this directive must go before the interface directive because dsc makes only one pass through the configuration file and the pcap buffer size is set when the interface is initialized.

pcap_thread_timeout MILLISECONDS ;
    Set the internal timeout pcap-thread uses when waiting for packets, the default is 100 ms. Note that this directive must go before the interface directive.

drop_ip_fragments ;
    Drop all packets that are fragments. Note that this directive must go before the interface directive.

interface IFACE | FILE ;
    The interface name to sniff packets from or a pcap file to read packets from. You may specify multiple interfaces by repeating the interface line any number of times. Under Linux (kernel v2.2+) libpcap can use an "any" interface which will include any interfaces the host has but these interfaces will not be put into promiscuous mode which may prevent capturing traffic that is not directly related to the host.

dnstap_file FILE ;
dnstap_unixsock FILE [ USER ][ :GROUP ] [ UMASK ] ;
dnstap_tcp IP PORT ;
dnstap_udp IP PORT ;
    Specify DNSTAP input from a file, UNIX socket, UDP or TCP connections (dsc will listen for incoming connections). This type of input is delivered directly from the DNS software itself as encapsulated DNS packets as seen or as made by the software. See https://dnstap.info (https://dnstap.info) for more information about DNSTAP. For UNIX sockets there are additional optional options to control access to it. The user and group access are specified together as strings (USER:GROUP), separated with a colon if a group is specified. The file permissions are controlled by a file mode creation mask (UMASK, must being with 0) which is set temporarily during socket creation. It is not necessary to specify all options, you can specify only USER, only :GROUP or only UMASK. Example below shows how to give read and write access to somegroup, remove permissions for others and how the resulting socket file permissions would be:
          dnstap_unixsock /path/to/file.sock :somegroup 0007;
          srwxrwx--- 1 root somegroup    0 Date dd HH:MM /path/to/file.sock
    NOTE:

    -   Only one DNSTAP input can be specified at a time currently.

    -   Configuration needs to match that of the DNS software.

dnstap_network IPV4 IPV6 PORT ;
    Specify DNSTAP network information. Per DNSTAP specification, some information may be not included such as receiver or sender of DNS. To be able to produce statistics, dsc needs to know what to put in place when that information is missing. This is configured by dnstap_network and should be the primary IP addresses and port of the DNS software. Default values are 127.0.0.1 ::1 53.

qname_filter NAME FILTER ;
    This directive allows you to define custom filters to match query names in DNS messages. Please see section QNAME FILTERS for more information.

datasets NAME TYPE LABEL:FIRST LABEL:SECOND FILTERS [ PARAMETERS ] ;
    This directive is the heart of dsc. However, it is also the most complex (see section DATASETS). See section EXAMPLE for a set of defined good datasets which is also installed as dsc.conf.sample.

bpf_vlan_tag_byte_order TYPE ;
    dsc knows about VLAN tags. Some operating systems (FreeBSD-4.x) have a bug whereby the VLAN tag id is byte-swapped. Valid values for this directive are host and net (the default). Set this to host if you suspect your operating system has the VLAN tag byte order bug.

match_vlan ID [ ID ... ] ;
    A white-space separated list of VLAN identifiers. If set, only the packets belonging to these VLANs are analyzed.

statistics_interval SECONDS ;
    Specify how often dsc should write statistics, default to 60 seconds.

no_wait_interval ;
    Do not wait on interval sync to start capturing, normally DSC will sleep for time() % statistics_interval to align with the minute (as was the default interval before) but now if you change the interval to more then a minute you can use with option to begin capture right away.

output_format FORMAT ;
    Specify the output format. You may specify multiple formats by repeating the output_format line any number of times. Default output format is XML, see section DATA FORMATS and FILE NAMING CONVENTIONS.

output_user USER ;
    Specify which user should own the output file, default to the user running dsc.

output_group GROUP ;
    Specify which group should own the output file, default to the group of the user running dsc.

output_mod FILE_MODE_BITS ;
    Specify the file mode bits (in octal) for the output file permissions, default to 0664.

dump_reports_on_exit ;
    Dump any remaining report before exiting. NOTE: Timing in the data files will be off!

geoip_v4_dat " FILE " [ OPTION ... ] ;
    Specify the GeoIP dat file to open for IPv4 country lookup, see section GEOIP for options.

geoip_v6_dat " FILE " [ OPTION ... ] ;
    Specify the GeoIP dat file to open for IPv6 country lookup, see section GEOIP for options.

geoip_asn_v4_dat " FILE " [ OPTION ... ] ;
    Specify the GeoIP dat file to open for IPv4 AS number lookup, see section GEOIP for options.

geoip_asn_v6_dat " FILE " [ OPTION ... ] ;
    Specify the GeoIP dat file to open for IPv6 AS number lookup, see section GEOIP for options.

asn_indexer_backend BACKEND ;
    Specify what backend to use for the ASN indexer, either "geoip" for GeoIP Legacy or "maxminddb" for MaxMind DB (GeoIP2).

country_indexer_backend BACKEND ;
    Specify what backend to use for the country indexer, either "geoip" for GeoIP Legacy or "maxminddb" for MaxMind DB (GeoIP2).

maxminddb_asn " FILE " ;
    Specify the MaxMind DB file to use for ASN lookups.

maxminddb_country " FILE " ;
    Specify the MaxMind DB file to use for country lookups.

client_v4_mask NETMASK ;
    Set the IPv4 MASK for client_subnet INDEXERS.

client_v6_mask NETMASK ;
    Set the IPv6 MASK for client_subnet INDEXERS.

response_time_mode MODE ;
    Set the output MODE of the response time indexer:

    bucket
        Count response time in buckets of microseconds, see response_time_bucket_size for setting the size of the buckets.

    log10
        Count response time in logarithmic scale with base 10.

    log2
        Count response time in logarithmic scale with base 2.

response_time_max_queries NUMBER ;
    Set the maximum number of queries to keep track of.

response_time_full_mode MODE ;
    If the number of queries tracked exceeds response_time_max_queries the MODE will control how to handle it:

    drop_query
        Drop the incoming query.

    drop_oldest
        Drop the oldest query being tracked and accept the incoming one.

response_time_max_seconds SECONDS ;
    Set the maximum seconds to keep a query but a query can still be matched to a response while being outside this limit, see response_time_max_sec_mode on how to handle those situations.

response_time_max_sec_mode MODE ;
    Control how to handle queries and responses which are match successfully but exceeds response_time_max_seconds:

    ceil
        The query will be counted as successful but the time it took will be the maximum seconds (think ceiling, or ceil()).

    timed_out
        The query will be counted as timed out.

response_time_bucket_size SIZE ;
    Control the size of bucket (microseconds) in bucket mode.

knowntlds_file FILE ;
    Load known TLDs from FILE, this should be or have the same format as https://data.iana.org/TLD/tlds-alpha-by-domain.txt.

tld_list FILE ;
    This option changes what DSC considers a TLD (similar to Public Suffix List) and affects any indexers that gathers statistics on TLDs, such as the tld, second_ld and third_ld indexers. The file format is simply one line per suffix and supports commenting out lines with #. You can use dsc-psl-convert to convert the Public Suffix List to this format, see dsc-psl-convert(5) for more information and examples on how to setup.

DATASETS
A dataset is a 2-D array of counters. For example, you might have a dataset with “Query Type” along one dimension and “Query Name Length” on the other. The result is a table that shows the distribution of query name lengths for each query type. A dataset has the following format: datasets NAME TYPE LABEL:FIRST LABEL:SECOND FILTERS [ PARAMETERS ] ;

NAME
    The name of the dataset, this must be unique and is used in the filename for the output files.

TYPE
    The protocol layer, available layers are:
        ip
        dns

LABEL
    The label of the dimensions.

FIRST
    The indexer for the first dimension, see INDEXERS sections.

SECOND
    The indexer for the second dimension, see INDEXERS sections.

FILTERS
    One or more filters, see FILTERS sections.

PARAMETERS
    Zero or more parameters, see section PARAMETERS.

INDEXERS AND FILTERS
An indexer is simply a function that transforms the attributes of an IP/DNS message into an array index. For some attributes the transformation is straightforward. For example, the “Query Type” indexer simply extracts the query type value from a DNS message and uses this 16-bit value as the array index. Other attributes are slightly more complicated. For example, the “TLD” indexer extracts the TLD of the QNAME field of a DNS message and maps it to an integer. The indexer maintains a simple internal table of TLD-to-integer mappings. The actual integer values are unimportant because the TLD strings, not the integers, appear in the resulting data. When you specify an indexer on a dataset line, you must provide both the name of the indexer and a label. The Label appears as an attribute in the output. For example the following line:
    dataset the_dataset dns Foo:foo Bar:bar queries-only;
Would produce the following XML output:
    <array name="the_dataset" dimensions="2" start_time="1091663940" ...
      <dimension number="1" type="Foo"/>
      <dimension number="2" type="Bar"/>
      <data>
        <Foo val="1">
          <Bar val="0" count="4"/>
          ...
          <Bar val="100" count="41"/>
        </Foo>
        <Foo val="2">
          ...
        </Foo>
      </data>
    </array>

IP INDEXERS
dsc includes only minimal support for collecting IP-layer stats. Mostly we are interested in finding out the mix of IP protocols received by the DNS server. It can also show us if/when the DNS server is the subject of denial-of-service attack.

ip_direction
    One of three values: sent, recv or else. Direction is determined based on the setting for local_address in the configuration file.

ip_proto
    The IP protocol type, e.g.: tcp, udp or icmp. Note that the bpf_program setting affects all traffic seen. If the program contains the word “udp” then you won't see any counts for non-UDP traffic.

ip_version
    The IP version number, e.g.: 4 or 6. Can be used to compare how much traffic comes in via IPv6 compared to IPv4.

IP FILTERS
Currently there is only one IP protocol filter: any. It includes all received packets.

DNS INDEXERS

certain_qnames
    This indexer isolates the two most popular query names seen by DNS root servers: localhost and [a--m].root-servers.net.

client_subnet
    Groups DNS messages together by the subnet of the client's IP address. The subnet is masked by /24 for IPv4 and by /96 for IPv6. We use this to make datasets with large, diverse client populations more manageable and to provide a small amount of privacy and anonymization.

client
    The IP (v4 and v6) address of the DNS client.

server
    The IP (v4 and v6) address of the DNS server.

country
    The country code of the IP (v4 and v6), see section GEOIP.

asn The AS (autonomous system) number of the IP (v4 and v6), see section GEOIP.

do_bit
    This indexer has only two values: 0 or 1. It indicates whether or not the “DO” bit is set in a DNS query. According to RFC 2335: Setting the DO bit to one in a query indicates to the server that the resolver is able to accept DNSSEC security RRs.

edns_version
    The EDNS version number, if any, in a DNS query. EDNS Version 0 is documented in RFC 2671.

edns_bufsiz
    The EDNS buffer size per 512 chunks (0-511, 512-1023 etc).

edns_cookie
    Indicates whether or not a EDNS(0) Cookie (RFC7873) was present with "yes" or "no".

edns_cookie_len
    The combined length of the EDNS(0) client and server cookies.

edns_cookie_client
    The EDNS(0) Client Cookie bytes as a hexadecimal string.

edns_cookie_server
    The EDNS(0) Server Cookie bytes as a hexadecimal string.

edns_ecs
    Indicates whether or not a EDNS(0) Client Subnet (RFC7871) was present with "yes" or "no".

edns_ecs_family
    The EDNS(0) Client Subnet address family.

edns_ecs_source_prefix
    The EDNS(0) Client Subnet source prefix-length.

edns_ecs_scope_prefix
    The EDNS(0) Client Subnet scope prefix-length.

edns_ecs_address
    The EDNS(0) Client Subnet address bytes as a hexadecimal string.

edns_ecs_subnet
    The EDNS(0) Client Subnet address as an IPv4/IPv6 textual address.

edns_ede
    Indicates whether or not a EDNS(0) Extended DNS Errors (RFC8914) was present with "yes" or "no".

edns_ede_code
    The EDNS(0) Extended DNS Errors code.

edns_ede_textlen
    The length of the EDNS(0) Extended DNS Errors extra-text.

edns_ede_text
    The EDNS(0) Extended DNS Errors extra-text.

edns_nsid
    Indicates whether or not a EDNS(0) DNS Name Server Identifier (RFC5001) was present with "yes" or "no".

edns_nsid_len
    The length of the EDNS(0) DNS Name Server Identifier (NSID).

edns_nsid_data
    The EDNS(0) DNS Name Server Identifier (NSID) bytes as a hexadecimal string.

edns_nsid_text
    The EDNS(0) DNS Name Server Identifier (NSID) as a string of printable characters. Unprintable characters are replaced with ".".

idn_qname
    This indexer has only two values: 0 or 1. It returns 1 when the first QNAME in the DNS message question section is an internationalized domain name (i.e., containing non-ASCII characters). Such QNAMEs begin with the string xn--. This convention is documented in RFC 3490.

msglen
    The overall length (size) of the DNS message.

null
    A “no-op” indexer that always returns the same value. This can be used to effectively turn the 2-D table into a 1-D array.

opcode
    The DNS message opcode is a four-bit field. QUERY is the most common opcode. Additional currently defined opcodes include: IQUERY, STATUS, NOTIFY, and UPDATE.

qclass
    The DNS message query class (QCLASS) is a 16-bit value. IN is the most common query class. Additional currently defined query class values include: CHAOS, HS, NONE, and ANY.

qname
    The full QNAME string from the first (and usually only) QNAME in the question section of a DNS message.

qnamelen
    The length of the first (and usually only) QNAME in a DNS message question section. Note this is the “expanded” length if the message happens to take advantage of DNS message “compression”.

label_count
    The number of labels (between "." dots) in the first (and usually only) QNAME in a DNS message question section. Note that a value of 0 (zero) means DNS root (.).

qtype
    The query type (QTYPE) for the first QNAME in the DNS message question section. Well-known query types include: A, AAAA, A6, CNAME, PTR, MX, NS, SOA, and ANY.

query_classification
    A stateless classification of “bogus” queries:

    non-auth-tld
        When the TLD is not one of the IANA-approved TLDs.

    root-servers.net
        A query for a root server IP address.

    localhost
        A query for the localhost IP address.

    a-for-root
        An “A” query for the DNS root (.).

    a-for-a
        An “A” query for an IPv4 address.

    rfc1918-ptr
        A PTR query for an RFC 1918 address.

    funny-class
        A query with an unknown/undefined query class, based on IANA DNS parameters.

    funny-qtype
        A query with an unknown/undefined query type, based on IANA DNS parameters.

    src-port-zero
        When the UDP message's source port equals zero.

    malformed
        A malformed DNS message that could not be entirely parsed.

rcode
    The RCODE value in a DNS response. The most common response codes are 0 (NO ERROR) and 3 (NXDOMAIN).

rd_bit
    This indexer returns 1 if the RD (recursion desired) bit is set in the query. Usually only stub resolvers set the RD bit. Usually authoritative servers do not offer recursion to their clients.

tc_bit
    This indexer returns 1 if the TC (truncated) bit is set (in a response). An authoritative server sets the TC bit when the entire response won't fit into a UDP message.

tld The TLD of the first QNAME in a DNS message's question section.

second_ld
    The Second LD of the first QNAME in a DNS message's question section.

third_ld
    The Third LD of the first QNAME in a DNS message's question section.

transport
    Indicates whether the DNS message is carried via UDP or TCP.

dns_ip_version
    The IP version number that carried the DNS message.

dns_source_port
    The source port of the DNS message.

dns_sport_range
    The source port of the DNS message per 1024 chunks (0-1023, 1024-2047 etc).

qr_aa_bits
    The "qr_aa_bits" dataset may be useful when dsc is monitoring an authoritative name server. This dataset counts the number of DNS messages received with each combination of QR,AA bits. Normally the authoritative name server should *receive* only *queries*. If the name server is the target of a DNS reflection attack, it will probably receive DNS *responses* which have the QR bit set.

response_time
    An indexer to track queries and return the response time in buckets along with other state buckets for timeouts, missing queries (received a response but have never seen the query), dropped queries (due to memory limitations) and internal errors. Queries are matched against responses by checking (in this order) the DNS ID, the IP version and protocol, client IP, client port, server IP and last server port. There are a few configuration options to control how response time statistics are gathered and handled, please see CONFIGURATION. NOTE: Only one instance of this indexer can be used in a dataset, this is due to the state to stores and the design of DSC.

encryption
    Indicates whether the DNS message was carried over an encrypted connection or not, and if so over which. For example "unencrypted", "dot" (DNS-over-TLS), "doh" (DNS-over-HTTPS). This information is only available via DNSTAP and if supported by the software generating it.

DNS FILTERS
You must specify one or more of the following filters (separated by commas) on the dataset line. Note that multiple filters are ANDed together. That is, they narrow the input stream, rather than broaden it.

any The no-op filter, counts all messages.

queries-only
    Count only DNS query messages. A query is a DNS message where the QR bit is set to 0.

replies-only
    Count only DNS response messages. A response is a DNS message where the QR bit is set to 1.

nxdomains-only
    Count only NXDOMAIN responses.

popular-qtypes
    Count only DNS messages where the query type is one of: A, NS, CNAME, SOA, PTR, MX, AAAA, A6, ANY.

idn-only
    Count only DNS messages where the query name is in the internationalized domain name format.

aaaa-or-a6-only
    Count only DNS messages where the query type is AAAA or A6.

root-servers-net-only
    Count only DNS messages where the query name is within the root-servers.net domain.

chaos-class
    Counts only DNS messages where QCLASS is equal to CHAOS (3). The CHAOS class is generally used for only the special hostname.bind and version.bind queries.

priming-query
    Count only DNS messages where the query type is NS and QNAME is “.”.

servfail-only
    Count only SERVFAIL responses.

authentic-data-only
    Count only DNS messages with the AD bit is set.

edns0-only
    Count only DNS messages with EDNS(0) options.

edns0-cookie-only
    Count only DNS messages with EDNS(0) Cookie option.

edns0-nsid-only
    Count only DNS messages with EDNS(0) DNS Name Server Identifier option.

edns0-ede-only
    Count only DNS messages with EDNS(0) Extended DNS Errors option.

edns0-ecs-only
    Count only DNS messages with EDNS(0) Client Subnet option.

QNAME FILTERS
Defines a custom QNAME-based filter for DNS messages. If you refer to this named filter on a dataset line, then only queries or replies for matching QNAMEs will be counted. The QNAME argument is a regular expression. For example:
    qname_filter WWW-Only ^www. ;
    dataset qtype dns All:null Qtype:qtype queries-only,WWW-Only ;

PARAMETERS
dsc currently supports the following optional parameters:

min-count=NN
    Cells with counts less than NN are not included in the output. Instead, they are aggregated into the special values -:SKIPPED:- and -:SKIPPED_SUM:-. This helps reduce the size of datasets with a large number of small counts.

max-cells=NN
    A different, perhaps better, way of limiting the size of a dataset. Instead of trying to determine an appropriate min-count value in advance, max-cells allows you put a limit on the number of cells to include for the second dataset dimension. If the dataset has 9 possible first-dimension values, and you specify a max-cell count of 100, then the dataset will not have more than 900 total values. The cell values are sorted and the top max-cell values are output. Values that fall below the limit are aggregated into the special -:SKIPPED:- and -:SKIPPED_SUM:- entries.

FILE NAMING CONVENTIONS
The filename is in the format:
    ${timestamp}.dscdata.${format}
For example:
    1154649660.dscdata.xml

DATA FORMATS

XML A dataset XML file has the following structure:
<array name="dataset-name" dimensions="2" start_time="unix-seconds"
        stop_time="unix-seconds">
  <dimension number="1" type="Label1"/>
  <dimension number="2" type="Label2"/>
  <data>
    <Label1 val="D1-V1">
      <Label2 val="D2-V1" count="N1"/>
      <Label2 val="D2-V2" count="N2"/>
      <Label2 val="D2-V3" count="N3"/>
    </Label1>
    <Label1 val="D1-V2">
      <Label2 val="D2-V1" count="N1"/>
      <Label2 val="D2-V2" count="N2"/>
      <Label2 val="D2-V3" count="N3"/>
    </Label1>
  </data>
</array>

JSON
    A dataset JSON file has the following structure:
{
  "name": "dataset-name",
  "start_time": unix-seconds,
  "stop_time": unix-seconds,
  "dimensions": [ "Label1", "Label2" ],
  "data": [
    {
      "Label1": "D1-V1",
      "Label2": [
        { "val": "D2-V1", "count": N1 },
        { "val": "D2-V2", "count": N2 },
        { "val": "D2-V3", "count": N3 }
      ]
    },
    {
      "Label1": "D1-V2-base64",
      "base64": true,
      "Label2": [
        { "val": "D2-V1", "count": N1 },
        { "val": "D2-V2-base64", "base64": true, "count": N2 },
        { "val": "D2-V3", "count": N3 }
      ]
    }
  ]
}
dataset-name, Label1, and Label2 come from the dataset definition. The start_time and stop_time attributes are given in Unix seconds. They are normally 60-seconds apart. dsc usually starts a new measurement interval on 60 second boundaries. That is:
    stop_time mod{60} == 0
The Label1 attributes (D1-V1, D1-V2) are values for the first dimension indexer. Similarly, the Label2 attributes (D2-V1, D2-V2 D2-V3) are values for the second dimension indexer. For some indexers these values are numeric, for others they are strings. If the value contains certain non-printable characters, the string is base64-encoded and the optional BASE64 attribute is set to 1/true. There are two special vals that help keep large datasets down to a reasonable size: -:SKIPPED:- and -:SKIPPED_SUM:-. These may be present on datasets that use the min-count and max-cells parameters (see section PARAMETERS). -:SKIPPED:- is the number of cells that were not included in the output. -:SKIPPED_SUM:-, is the sum of the counts for all the skipped cells. Note that “one-dimensional datasets” still use two dimensions in the output. The first dimension type and value will be “All” as shown in the example below:
    <array name="rcode" dimensions="2" start_time="1154649600"
            stop_time="1154649660">
      <dimension number="1" type="All"/>
      <dimension number="2" type="Rcode"/>
      <data>
        <All val="ALL">
          <Rcode val="0" count="70945"/>
          <Rcode val="3" count="50586"/>
          <Rcode val="4" count="121"/>
          <Rcode val="1" count="56"/>
          <Rcode val="5" count="44"/>
        </All>
      </data>
    </array>
The count values are always integers. If the count for a particular tuple is zero, it should not be included in the output. Note that the contents of the output do not indicate where it came from. In particular, the server and node that it came from are not present.

GEOIP
Country code and AS number lookup is available using MaxMind GeoIP Legacy API if it was enabled during compilation. Multiple options can be give to the database and are directly linked to the options for GeoIP_open() but without the prefix of GEOIP_, example:
    geoip_v4_dat "/usr/local/share/GeoIP/GeoIP.dat" STANDARD MEMORY_CACHE;
    geoip_asn_v6_dat "/usr/local/share/GeoIP/GeoIPASNumv6.dat" MEMORY_CACHE;
GeoIP documentation says:

STANDARD
    Read database from file system. This uses the least memory.

MEMORY_CACHE
    Load database into memory. Provides faster performance but uses more memory.

CHECK_CACHE
    Check for updated database. If database has been updated, reload file handle and/or memory cache.

INDEX_CACHE
    Cache only the the most frequently accessed index portion of the database, resulting in faster lookups than GEOIP_STANDARD, but less memory usage than GEOIP_MEMORY_CACHE. This is useful for larger databases such as GeoIP Legacy Organization and GeoIP Legacy City. Note: for GeoIP Legacy Country, Region and Netspeed databases, GEOIP_INDEX_CACHE is equivalent to GEOIP_MEMORY_CACHE.

MMAP_CACHE
    Load database into mmap shared memory. MMAP is not available for 32bit Windows.

EXAMPLE
local_address 127.0.0.1;
local_address ::1;
#local_address 127.0.0.0 255.0.0.0;
#local_address 192.168.0.0 24;
#local_address 10.0.0.0 8;
run_dir "/var/lib/dsc";
minfree_bytes 5000000;
pid_file "/run/dsc.pid";
# Example filters
#
#bpf_program "udp port 53";
#bpf_program "tcp port 53 or udp port 53";
# Use this to see only DNS *queries*
#
#bpf_program "udp dst port 53 and udp[10:2] & 0x8000 = 0";
#dns_port 53;
#pcap_buffer_size 4194304;
#pcap_thread_timeout 100;
#drop_ip_fragments;
interface eth0;
#interface any;
#dnstap_file /path/to/file.dnstap;
#dnstap_unixsock /path/to/unix.sock;
#dnstap_tcp 127.0.0.1 5353;
#dnstap_udp 127.0.0.1 5353;
#dnstap_network 127.0.0.1 ::1 53;
dataset qtype dns All:null Qtype:qtype queries-only;
dataset rcode dns All:null Rcode:rcode replies-only;
dataset opcode dns All:null Opcode:opcode queries-only;
dataset rcode_vs_replylen dns Rcode:rcode ReplyLen:msglen replies-only;
dataset client_subnet dns All:null ClientSubnet:client_subnet queries-only max-cells=200;
dataset qtype_vs_qnamelen dns Qtype:qtype QnameLen:qnamelen queries-only;
dataset qtype_vs_tld dns Qtype:qtype TLD:tld queries-only,popular-qtypes max-cells=200;
dataset certain_qnames_vs_qtype dns CertainQnames:certain_qnames Qtype:qtype queries-only;
dataset client_subnet2 dns Class:query_classification ClientSubnet:client_subnet queries-only max-cells=200;
dataset client_addr_vs_rcode dns Rcode:rcode ClientAddr:client replies-only max-cells=50;
dataset chaos_types_and_names dns Qtype:qtype Qname:qname chaos-class,queries-only;
#dataset country_code dns All:null CountryCode:country queries-only;
#dataset asn_all dns IPVersion:dns_ip_version ASN:asn queries-only max-cells=200;
dataset idn_qname dns All:null IDNQname:idn_qname queries-only;
dataset edns_version dns All:null EDNSVersion:edns_version queries-only;
dataset edns_bufsiz dns All:null EDNSBufSiz:edns_bufsiz queries-only;
dataset do_bit dns All:null D0:do_bit queries-only;
dataset rd_bit dns All:null RD:rd_bit queries-only;
dataset idn_vs_tld dns All:null TLD:tld queries-only,idn-only;
dataset ipv6_rsn_abusers dns All:null ClientAddr:client queries-only,aaaa-or-a6-only,root-servers-net-only max-cells=50;
dataset transport_vs_qtype dns Transport:transport Qtype:qtype queries-only;
dataset client_port_range dns All:null PortRange:dns_sport_range queries-only;
#dataset second_ld_vs_rcode dns Rcode:rcode SecondLD:second_ld replies-only max-cells=50;
#dataset third_ld_vs_rcode dns Rcode:rcode ThirdLD:third_ld replies-only max-cells=50;
dataset direction_vs_ipproto ip Direction:ip_direction IPProto:ip_proto any;
#dataset dns_ip_version_vs_qtype dns IPVersion:dns_ip_version Qtype:qtype queries-only;
#dataset response_time dns All:null ResponseTime:response_time;
#dataset priming_queries dns Transport:transport EDNSBufSiz:edns_bufsiz priming-query,queries-only;
#dataset priming_responses dns All:null ReplyLen:msglen priming-query,replies-only;
#dataset qr_aa_bits dns Direction:ip_direction QRAABits:qr_aa_bits any;
#dataset servfail_qname dns ALL:null Qname:qname servfail-only,replies-only;
#dataset ad_qname dns ALL:null Qname:qname authentic-data-only,replies-only;
#dataset label_count dns All:null LabelCount:label_count any;
#dataset encryption dns All:null Encryption:encryption queries-only;
#statistics_interval 60;
#no_wait_interval;
output_format XML;
#output_format JSON;
#output_user root;
#output_group root;
#output_mod 0664;
#geoip_v4_dat "/usr/share/GeoIP/GeoIP.dat" STANDARD MEMORY_CACHE MMAP_CACHE;
#geoip_v6_dat "/usr/share/GeoIP/GeoIPv6.dat";
#geoip_asn_v4_dat "/usr/share/GeoIP/GeoIPASNum.dat" MEMORY_CACHE;
#geoip_asn_v6_dat "/usr/share/GeoIP/GeoIPASNumv6.dat" MEMORY_CACHE;
#asn_indexer_backend geoip;
#country_indexer_backend geoip;
#maxminddb_asn "/path/to/GeoLite2/ASN.mmdb";
#maxminddb_country "/path/to/GeoLite2/Country.mmdb";
#client_v4_mask 255.255.255.0;
#client_v6_mask ffff:ffff:ffff:ffff:ffff:ffff:0000:0000;
#response_time_mode log10;
#response_time_max_queries 1000000;
#response_time_full_mode drop_query;
#response_time_max_seconds 5;
#response_time_max_sec_mode ceil;
#response_time_bucket_size 100;
#knowntlds_file file;

FILES
@etcdir@/dsc.conf
@etcdir@/dsc.conf.sample

SEE ALSO
dsc(1), dsc-psl-convert(1)

AUTHORS
Jerry Lundström, DNS-OARC
Duane Wessels, Measurement Factory / Verisign
Ken Keys, Cooperative Association for Internet Data Analysis
Sebastian Castro, New Zealand Registry Services

Maintained by DNS-OARC

    https://www.dns-oarc.net/tools/dsc

BUGS
For issues and feature requests please use:

    @PACKAGE_URL@

For question and help please use:

    @PACKAGE_BUGREPORT@