Awesome
Transdep
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.
Licence
Transdep is licenced under the 2-clause BSD licence.
Installation
Transdep uses the following external libraries:
- https://github.com/miekg/dns
- https://github.com/awalterschulze/gographviz
- https://github.com/hashicorp/golang-lru
- https://github.com/deckarep/golang-set
- https://github.com/hashicorp/go-immutable-radix
You may install them using the go get command or whichever other method you prefer:
$ go get github.com/miekg/dns
$ go get github.com/awalterschulze/gographviz
$ go get github.com/hashicorp/golang-lru
$ go get github.com/deckarep/golang-set
$ go get github.com/hashicorp/go-immutable-radix
You may then use the Makefile to compile the Transdep tools:
$ make all
Usage
CLI
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 www.example.net
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 "example.com\nexample.net")
./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 example.net -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 www.example.com -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 www.x-cli.eu -break4
www.x-cli.eu:this domain name requires some IPv4 addresses to be resolved properly
./transdep -domain www.example.com -break4
www.example.com.:Name:example.com.
www.example.com.:IP:2001:500:8d::53
www.example.com.:Name:iana-servers.net.
www.example.com.:Name:.
www.example.com.:Name:net.
www.example.com.:Name:com.
In the previous example, www.x-cli.eu.
cannot be resolved by IPv6-only resolvers (because some names or delegations do
not have IPv6 addresses).
For www.example.com
, 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 www.example.com
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 www.x-cli.eu -all
AllNames:www.x-cli.eu.:Name:x-cli.eu.
AllNames:www.x-cli.eu.:Name:.
AllNames:www.x-cli.eu.:Name:eu.
DNSSEC:www.x-cli.eu.:Name:.
DNSSEC:www.x-cli.eu.:Name:eu.
AllNamesNo4:www.x-cli.eu.:this domain name requires some IPv4 addresses to be resolved properly
DNSSECNo4:www.x-cli.eu.:this domain name requires some IPv4 addresses to be resolved properly
AllNamesNo6:www.x-cli.eu.:Name:eu.
AllNamesNo6:www.x-cli.eu.:Name:x-cli.eu.
AllNamesNo6:www.x-cli.eu.:Name:.
DNSSECNo6:www.x-cli.eu.:Name:.
DNSSECNo6:www.x-cli.eu.:Name:eu.
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:
64501 192.0.2.0/24
64501 198.51.100.0/24
64502 203.0.113.0/24
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 www.example.com -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 forDomainName
to be resolvable.IP
: the next field specifies an IP address that must be available and not hijacked forDomainName
to be resolvable.Prefix:
: the next field specifies a network prefix that must be available and not hijacked forDomainName
to be resolvable.ASN:
: the next field specifies an AS number whose whole network must not be totally broken forDomainName
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 www.x-cli.eu | dot -T pdf -o /tmp/graph_x-cli.eu.pdf
Caches
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.
Concurrency
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 http://127.0.0.1:5000
.
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 thetransdep
CLI utility./dnssec
is the endpoint corresponding to the-dnssec
option of thetransdep
CLI utility./break4
is the endpoint corresponding to the-break4
option of thetransdep
CLI utility./break6
is the endpoint corresponding to the-break6
option of thetransdep
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 http://127.0.0.1:5000/stop?secret=5942985ebdc9102663130752c1d21f23
$ curl http://127.0.0.1:5000/stop?secret=5942985ebdc9102663130752c1d21f23
Stopping.
Stopping the finder: OK
$