Understanding Tor Relay Flags: Running, Valid, Fast, Stable, HSDir, and Guard

Tor relay flags describe what the network currently knows about a relay and which roles that relay is eligible to perform.

They are not badges manually assigned by Tor Project staff. Most are calculated automatically by Directory Authorities according to protocol rules and network measurements.

Running

Running means the Directory Authorities currently consider the relay reachable.

A relay that is publicly accessible and responding correctly on its ORPort can receive this flag relatively quickly.

Conceptually:

ORPort reachable
     ↓
Authority confirms connectivity
     ↓
Running

Losing Internet connectivity for long enough can cause the flag to disappear. It can return after reachability is restored.

Valid

Valid means the relay is accepted as a valid participant in the Tor network.

It is not a performance rating.

A relay may be:

Valid

while still being:

slow
new
lightly used

The flag primarily indicates that the relay has not been excluded from normal consideration.

V2Dir

V2Dir indicates that the relay can participate in Tor directory-cache functionality.

The name is historical and can be confusing.

Most importantly:

V2Dir ≠ Directory Authority

A V2Dir relay is still an ordinary relay.

Fast

Fast indicates that the relay satisfies the Tor network’s current bandwidth criteria for fast-relay use.

This flag depends primarily on measured network capacity rather than age alone.

A newly deployed relay may therefore progress:

Running
Valid
V2Dir
   ↓
bandwidth measurement
   ↓
Fast

There is no universal rule such as:

12 hours online = Fast

The result depends on measurement timing and the current network-wide threshold.

For a capable new relay, obtaining Fast can occur within hours or days.

Stable

Stable is much more dependent on historical behavior.

It reflects metrics related to long-term reliability, including weighted mean time between failures.

A relay that repeatedly disappears and reappears will have more difficulty becoming Stable than a continuously available relay.

This is why:

current uptime

and:

historical stability

are not the same thing.

A relay can restart and later still be considered Stable because the decision incorporates longer-term history.

The realistic time scale is typically days rather than hours.

HSDir

HSDir means the relay is eligible to participate in the distributed directory system used by onion services.

An HSDir does not host the onion service itself.

Its role is associated with onion-service descriptor storage and retrieval.

Eligibility generally depends on conditions including:

Fast
+
Stable
+
sufficient continuous known time

A newly deployed relay therefore cannot immediately become an HSDir.

A minimum time scale of several days is expected.

Guard

Guard is one of the most significant relay flags.

Guard relays can be selected as the first hop in a Tor circuit:

Client
  ↓
Guard
  ↓
Middle
  ↓
Exit

Tor deliberately applies stricter requirements to Guards because the first relay directly observes the client’s network address.

Guard eligibility depends on a combination of:

• bandwidth
• Fast status
• Stable status
• uptime history
• time known to the authorities
• other network thresholds

For this reason, Guard is generally a weeks-scale milestone rather than an hours-scale milestone.

Exit

Exit means the relay is eligible to send Tor traffic to destinations on the ordinary Internet.

A relay configured with a policy equivalent to:

reject *:*

cannot operate as a normal Exit and therefore does not receive the Exit role.

This distinction is operationally important because Exit relays have significantly different abuse and legal exposure from non-exit relays.

BadExit

BadExit is an administrative safety flag used when a relay should not be trusted for normal Exit operation.

It does not necessarily mean:

server compromised

It means the network has determined that the relay should not be selected as a normal exit.

Authority

Authority identifies one of the small number of Tor Directory Authorities.

Ordinary relay operators cannot simply enable this flag.

Directory Authorities form part of Tor’s network-governance infrastructure and participate in producing the consensus.

MiddleOnly

MiddleOnly indicates a relay that should be used only in middle positions rather than as Guard or Exit.

It is relatively uncommon compared with flags such as Running, Valid, Fast, or Stable.

Flags Can Be Combined

Flags are not mutually exclusive.

A mature non-exit Guard relay might show:

Fast
Guard
Running
Stable
V2Dir
Valid

while a brand-new relay might initially show only:

Running
Valid
V2Dir

Approximate Time Scales

A practical way to think about relay development is:

First hours:
Running / Valid / V2Dir

Hours to days:
Fast

Days to a week or longer:
Stable

Several days or more:
HSDir

Weeks:
Guard

These are observation ranges, not guaranteed deadlines.

Conclusion

Tor flags answer a different question from bandwidth or connection count.

They describe eligibility and network status:

Running → Is it reachable?
Valid   → Is it accepted?
Fast    → Is it sufficiently fast?
Stable  → Has it proven reliable?
HSDir   → Can it participate in onion-service directory functions?
Guard   → Can it protect the first hop of client circuits?
Exit    → Can it send traffic to the public Internet?

For relay operators, the best way to earn the later flags is remarkably simple: maintain a reachable, well-performing, continuously available relay and allow the directory system to accumulate history.