# Probe Tags
RIPE Atlas probes may be tagged to indicate properties, capabilities, network topology or any other information. There are two kinds of tags: user tags and system tags. Each tag consists of a human-readable name, possibly including spaces, and a hyphenated "slug" that is used when interacting with the API.
You can search for probes with a particular combination of tags using the API - see the API documentation (opens new window) for details.
# User Tags
User tags may be applied and removed by the probe owner by going to the probes list (opens new window), selecting the desired probe and choosing "Edit". It is then possible to select from a list of commonly used tags, or create a custom tag. We periodically review custom tags so we can merge similar ones and suggest them to other users.
# System Tags
The RIPE Atlas system periodically applies special tags to probes. These tags can be recognised through the following characteristics:
- Their human-readable name begins with "system:", or they appear in the "System Tags" section on the probe page.
- Their "slug", used for querying the API, begins with "system-".
It is impossible for a RIPE Atlas user, including probe owners, to apply or remove a system tag, or to create a tag that begins with a "system" prefix.
# Methodology
Probes are re-assessed every four hours for each tag by inspecting certain baseline RIPE Atlas measurement results. The lookback period for this inspection is also four hours. If, for some reason, there are no results from a probe, such as when it has been offline for a while, then no tags will be added or removed.
# Tags
Several categories of system tags are assigned to probes:
# Basic Connectivity
These tags indicate whether RIPE Atlas believes a probe works or does not work over IPv4 and IPv6. A probe is considered to work over a particular IP version if it has at least one successful ping result for any one of a selection of baseline targets. It is considered to not work if it only returns failures.
If there are no results for one IP version, but there are results for the other version, then any existing tag for the first version will be removed.
The selection of measurement targets is diverse in that it includes anycast and unicast servers belonging to different organisations and having different purposes.
- system: IPv4 Works (system-ipv4-works)
- system: IPv4 Doesn't Work (system-ipv4-doesnt-work)
- system: IPv6 Works (system-ipv6-works)
- system: IPv6 Doesn't Work (system-ipv6-doesnt-work)
# Protocol Capability
- system: IPv4 Capable (system-ipv4-capable)
- system: IPv6 Capable (system-ipv6-capable)
- system: IPv4 RFC1918 address is configured (system-ipv4-rfc1918)
- system: IPv6 ULA is configured (system-ipv6-ula)
# DNS Resolution
These tags indicate whether a probe can resolve simple hostname records to the expected IP address. A probe is considered to be able to resolve if there is at least one correct response from each of its local resolvers. It is considered unable to reliably resolve if at least one of its local resolvers only returns failures. It is considered to resolve incorrectly if there is at least one incorrect result for each queried A or AAAA record.
If a probe submits any results from any of its local resolvers in which the name in the question section of the DNS request does not match the name in the answer section of the DNS reply in terms of upper/lower case (a 0x20 bit check (opens new window)), then it is tagged as mangling the cases and no other DNS tags will be applied.
- system: Can Resolve A (system-can-resolve-a)
- system: Resolves A Incorrectly (system-resolves-a-incorrectly)
- system: Cannot Resolve A (system-cannot-resolve-a)
- system: Can Resolve AAAA (system-can-resolve-aaaa)
- system: Resolves AAAA Incorrectly (system-resolves-aaaa-incorrectly)
- system: Cannot Resolve AAAA (system-cannot-resolve-aaaa)
- system: Resolver Mangles Case (system-resolver-mangles-case)
The A and AAAA records used for these tests are delegated to various unrelated DNS servers.
####Probe Metadata
These tags are not based on measurement results. Instead, they reflect a probe's intrinsic properties, such as its version (1, 2 or 3), and whether or not it is also a RIPE Atlas anchor (opens new window).
- system: V1 (system-v1)
- system: V2 (system-v2)
- system: V3 (system-v3)
- system: Anchor (system-anchor)