NAME

DESCRIPTION

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.

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 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:

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, can be give multiple times to output in more then one format. Default output format is XML, see section DATA FORMATS and FILE NAMING CONVENTIONS.

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:

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:

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:

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.

DATASETS

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

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

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

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).

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”.

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:

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.

DNS FILTERS

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.

QNAME FILTERS

    qname_filter WWW-Only ^www. ;
    dataset qtype dns All:null Qtype:qtype queries-only,WWW-Only ;

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

    ${timestamp}.dscdata.${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

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;
#statistics_interval 60;
#no_wait_interval;
output_format XML;
#output_format JSON;
#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/GeoList2/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

SEE ALSO

AUTHORS

Maintained by DNS-OARC

BUGS

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