ZDNS

ZDNS is a command-line utility that provides high-speed DNS lookups. For example, the following will perform MX lookups and a secondary A lookup for the IPs of MX servers for the domains in the Alexa Top Million:

cat top-1m.csv | zdns MX --lookup-ipv4 --alexa

ZDNS is written in golang and is primarily based on https://github.com/miekg/dns.

Install

ZDNS can be installed by running:

go get github.com/zmap/zdns/zdns

Usage

ZDNS provides several types of modules.

Raw DNS Modules

The A, AAAA, ANY, AXFR, CAA, CNAME, DMARC, MX, NS, PTR, TXT, SOA, and SPF modules provide the raw DNS response in JSON form, similar to dig.

For example, the command:

echo "censys.io" | zdns A

returns:

{
  "name": "censys.io",
  "status": "NOERROR",
  "data": {
    "answers": [
      {
        "ttl": 300,
        "type": "A",
        "name": "censys.io",
        "data": "216.239.38.21"
      }
    ],
    "additionals": [
      {
        "ttl": 34563,
        "type": "A",
        "name": "ns-cloud-e1.googledomains.com",
        "data": "216.239.32.110"
      },
    ],
    "authorities": [
      {
        "ttl": 53110,
        "type": "NS",
        "name": "censys.io",
        "data": "ns-cloud-e1.googledomains.com."
      },
    ],
    "protocol": "udp"
  }
}

Lookup Modules

Raw DNS responses frequently do not provide the data you want. For example, an MX response may not include the associated A records in the additionals section requiring an additional lookup. To address this gap and provide a friendlier interface, we also provide several lookup modules: alookup and mxlookup.

mxlookup will additionally do an A lookup for the IP addresses that correspond with an exchange record. alookup acts similar to nslookup and will follow CNAME records.

For example,

echo "censys.io" | ./zdns mxlookup --ipv4-lookup

returns:

{
  "name": "censys.io",
  "status": "NOERROR",
  "data": {
    "exchanges": [
      {
        "name": "aspmx.l.google.com",
        "type": "MX",
        "preference": 1,
        "ipv4_addresses": [
          "74.125.28.26"
        ],
        "ttl": 288
      },
      {
        "name": "alt1.aspmx.l.google.com",
        "type": "MX",
        "preference": 5,
        "ipv4_addresses": [
          "64.233.182.26"
        ],
        "ttl": 288
      }
    ]
  }
}

Zone File Modules

The above modules are useful when we only have a list of domain names to perform queries for. However, in some instances we have a root zone file that indicates all domains in a zone, and their nameservers. For this instance, we have the zone module.

The zone module performs an alookup for each domain in the specified zone file, skipping as much of the recursive lookup as is possible. This entails utilization of the glue records in the zone file to go directly to the domain's authoritative nameserver, as well as caching nameserver locations when lookups must be performed.

For example, if the following two records are in a zonefile,

foo.com. NS ns.foo.com.
ns.foo.com. A XXX.XXX.XXX.XXX

then the resulting lookup for foo.com will utilize the nameserver at XXX.XXX.XXX.XXX

This is useful for performing many alookup calls without hammering the local and root nameservers.

Note: the zone module requires the --input-file flag be set, in order to allow it to make two passes over the input.

Running ZDNS

By default, ZDNS will operate with 1,000 light-weight go routines. If you're not careful, this will overwhelm many upstream DNS providers. We suggest that users coordinate with local network administrators before performing any scans. You can control the number of concurrent connections with the --threads and --go-processes command line arguments. Alternate name servers can be specified with --name-servers. ZDNS will rotate through these servers when making requests.

Unsupported Types

If zdns encounters a record type it does not support it will generate an output record with the type field set correctly and a representation of the underlying data structure in the unparsed_rr field. Do not rely on the presence or structure of this field. This field (and its existence) may change at any time as we expand support for additional record types. If you find yourself using this field, please consider submitting a pull-request adding parser support.

License

ZDNS Copyright 2016 Regents of the University of Michigan

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See LICENSE for the specific language governing permissions and limitations under the License.