Discover SPOF in DNS dependency graphs
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Transdep is a utility to discover single points of failure (SPOF) in DNS dependency graphs leading to unability to resolve domain names.

DNS dependency graph is a notion that was introduced by Venugopalan Ramasubramanian and Emin Gün Sirer in Perils of Transitive Trust in the Domain Name System.

Current types of single points of failure that are detected are :

  • domain names (which can be availability SPOF if DNSSEC is incorrectly configured);
  • IP addresses of name servers;
  • Longest network prefixes that may generally be announced over the Internet (/24 over IPv4 and /48 over IPv6);
  • ASN of the AS announcing the IP addresses of name servers.

The transdep utility is the CLI version of the tool. The webserver utility spawns a REST/JSON webservice. Endpoints are described below.


Transdep is licenced under the 2-clause BSD licence.


Transdep uses the following external libraries:

You may install them using the go get command or whichever other method you prefer:

$ go get
$ go get
$ go get
$ go get
$ go get

You may then use the Makefile to compile the Transdep tools:

$ make all



The transdep utility can be used to analyze the dependencies of a single domain name, of multiple names, or a saved dependency graph.

Analysis Target Types

To analyze a single name, the -domain option is to be used:

./transdep -domain

To analyze multiple domain names, you must provide a list stored in a file with one domain name per line, with the option -file:

./transdep -file <(echo -ne "\")

./transdep -file /tmp/list_of_domain_names

If you saved a dependency graph into a file (that was generated using the -graph option ), you may analyze it by loading the graph with the -load option:

./transdep -domain -graph > /tmp/example_net_graph.json

./transdep -load /tmp/example_net_graph.json

Analysis Nature

Transdep can analyze a domain based on multiple criteria.

All analysis types consider that IP addresses and announcing network prefixes may be SPOF.

By default, SPOF discovery is conducted while considering that all names may break, including non-DNSSEC protected domain names. This is used to analyze SPOF in the event of misconfigurations, zone truncation and all other types of zone corruptions that may render a zone impossible to resolve.

If the analysis must be constrained to only consider that DNSSEC protected names may break, the -dnssec option must be added to the command line:

./transdep -domain -dnssec

By default, the SPOF discovery considers that resolvers are connected to both IPv4 and IPv6 networks. This means that if an IPv4 address is unavailable, this unavailibility may be covered for by a server available over IPv6.

In some scenarii, this is unacceptable, because the IPv4 resolvers and the IPv6 resolvers are separate servers. Also, one of these two networks might be unavailable (temporarily or permanently). To represent these situations, the -break4 (resp. -break6) options simulates that all IPv4 (resp. IPv6) addresses are always considered unavailable when analyzing the SPOF potential of an IP address in the other network type:

./transdep -domain -break4 domain name requires some IPv4 addresses to be resolved properly

./transdep -domain -break4

In the previous example, cannot be resolved by IPv6-only resolvers (because some names or delegations do not have IPv6 addresses). For, the result shows that during that run, Transdep detected that when using a resolver that has only access to the IPv6 network at the time of resolution, the name might not be possible to resolve if the IP address 2001:500:8d::53 is unavailable.

The -all option indicates to Transdep to analyze the requested domain name(s), using all possible compositions of the previous options: with and without -dnssec, and with and without -break4 or with and without -break6.

./transdep -domain -all domain name requires some IPv4 addresses to be resolved properly domain name requires some IPv4 addresses to be resolved properly

Transdep may also consider an analysis criterion based on the ASN of the AS announcing the network prefixes covering the IP addresses of the name servers. The association between the ASN and the IP address is done by using a file whose format is as follows:

  • one association per line;
  • each line contains an ASN and an announced network prefix.

Here is an example of such a file:

64502 2001:db8::/32

Such a file can be generated from a MRT dump file (bviews) such as the ones made available by the RIS project, using ANSSI's mabo tool with the sub-command prefixes.

The ASN-prefix file is provided to Transdep using the -mabo option:

./mabo prefixes bview.20171013.0800.gz > prefixes-20171013.txt
./transdep -domain -mabo prefixes-20171013.txt

Output Types

Transdep can generate several types of documents. By default, it generates a CSV containing the discovered SPOF for the requested analysis.

If the -all option is provided, the format is AnalysisType:DomainName:TypeOfSPOF:SPOFReference, where AnalysisType indicates one of the following combinations:

  • AllNames: default options (no -dnssec, no -break4, no -break6);
  • AllNamesNo4: default options except that -break4 is specified;
  • AllNamesNo6: default options except that -break6 is specified;
  • DNSSEC: default options except that -dnssec is specified;
  • DNSSECNo4: -dnssec and -break4 options are specified;
  • DNSSECNo6: -dnssec and -break6 options are specified.

If the -all option is not specified, the format is DomainName:TypeOfSPOF:SPOFRerefence.

In both formats, DomainName indicates the domain name that is analyzed.

TypeOfSPOF can value:

  • Name: the next field specifies a domain name that must be resolvable for DomainName to be resolvable.
  • IP: the next field specifies an IP address that must be available and not hijacked for DomainName to be resolvable.
  • Prefix:: the next field specifies a network prefix that must be available and not hijacked for DomainName to be resolvable.
  • ASN:: the next field specifies an AS number whose whole network must not be totally broken for DomainName to be resolvable.

TypeOfSPOF may also value a special value: Cycle. Cycle indicates that there is a circular dependency in the graph somewhere, or an overly long CNAME chain (for some definition of "overly long"). Having Cycle as dependency means that the name cannot be resolved at all using a RFC-compliant resolver at the time of resolution.

The -graph output option generates an output that can be later loaded for analysis using the -load option, described above.

The -dot output option generates a DOT file output. This output may be passed to any Graphviz interpret for graph drawing. The generated DOT file will highlight domain name and IP addresses that are SPOF by coloring the nodes in red.

./transdep -domain | dot -T pdf -o /tmp/


Transdep maintains several caches in order to limit the number of requests to name servers during the discovery of the dependency graph. There are in-memory caches, using LRU lists and go routines, and on-disk caches for long term cache and to store value overflowing from the in-memory LRU lists.

In-memory cache sizes are controlled with the -nrlrusize, -zcflrusize and -dflrusize options. The first two options are associated with lists that contain data that is cached on disk when the LRU lists are overflowing. The on-disk cache is leverage whenever possible and the entry is reinstated in the LRU list upon usage. Thus, an entry is either in-memory or on-disk and is never lost unless the cache directoy is flushed manually. The third option is associated with a LRU list whose entries may be very large. These entries are synthetized from the entries of the other caches, and thus are not stored on disk when the list is overflowing.

If your computer swaps or consumes too much memory while running Transdep, you should try to lower these values, trying to lower -dflrusize value first. If your computer spends too much time in "disk I/O wait" and you have some RAM capacity available, you may try to increase the two first options.

On-disk caches consist of a lot very small JSON files. Please monitor the number of remaining inodes and adapt your inode table accordingly.

On-disk caches are stored in the directory designated by the TMPDIR environment variable, the -cachedir command line option. The default value is /tmp.

Transdep caches never expire, with the current implementation. If you need to flush the cache, you may change the cache directory to keep the previous one and yet start fresh. You may also delete the nameresolver and zonecut directories that are present in the designated cache directory.

Root Zone Hint File

You may specify a root zone hint file with the -hints option. If left unspecified, a hard-coded list of root-servers will be used by Transdep, when querying the root zone for delegations.

DNS Violations

Using a RFC-compliant implementation prevents you from resolving many domain names. Thus, some degree of DNS violation tolerance was implemented in Transdep, with much grumble. By default, Transdep will consider rcode 3 status on non-terminal nodes equivalent to rcode 0 answers with ancount=0. You may reinstate RFC8020 compliance with the -rfc8020 option.

Some devices are also unable to answer to non-A/AAAA queries and always return rcode 2 answers for any other qtype, including NS or DS. By default, Transdep considers this servers as broken, but you may use the -servfail option to indicate Transdep to treat these answers as rcode 0 answers with ancount=0. This may lead Transdep to return incorrect results in some instances.

Script Friendliness

If you don't care about the nature of errors that may arise during the analysis of a domain name or if you want to have a output that is easily parsable, you may use the -script option to return errors as the constant -ERROR-.

Transdep will return an error if any name that is part of the dependency graph cannot be resolved at the time of dependency graph discovery. Doing otherwise might have led to incorrect results from partial dependency graph discovery.


You may adapt the number of domain names whose dependency graphs are discovered simultaneously with the -jobs option. The higher this option value, the more you will harass the name servers. You will want to keep this value relatively low, to prevent blacklisting of your IP and false measurements.

Web Service

The webservice uses the webserver binary.

The -bind and -port can be used to specify, respectively, on which address and port the web server should listen on. By default, the service is available on

The -nrlrusize, -zcflrusize, -dflrusize, -jobs, -hints and -cachedir options have the same usage as for the Transdep CLI utility.

The web server exposes several endpoints:

  • /allnames is the endpoint corresponding to the default behaviour of the transdep CLI utility.
  • /dnssec is the endpoint corresponding to the -dnssec option of the transdep CLI utility.
  • /break4 is the endpoint corresponding to the -break4 option of the transdep CLI utility.
  • /break6 is the endpoint corresponding to the -break6 option of the transdep CLI utility.

Combination of -dnssec and -break4 or -break6 is not possible with the web server.

Each endpoint takes a domain parameter as part of the query string, to specify which domain name is to be analyzed.

Endpoints may also receive rfc8020 and servfail query string parameters to indicate which DNS violations are tolerated for this analysis. If these options are not specified, rcode 3 answers on non-terminal nodes are treated as rcode 0 answers with ancount=0 and rcode 2 answers are considered as broken name servers.

When launched from a console, the webserver utility outputs a URL to query to gracefully stop the service. Gracefully shutting down the service is strongly advised to prevent on-disk cache corruption or incompleteness.

$ ./webserver &
[1] 7416
To stop the server, send a query to
$ curl
Stopping the finder: OK