Public Relay

Expanded Definition

A public relay is an intermediary service that forwards session traffic between endpoints when direct peer-to-peer connectivity is blocked by network address translation, firewall policy, or restrictive routing. In security and operations terms, it is a reachability bridge rather than a trust anchor: it helps the session establish, but it does not eliminate the need to secure the endpoints, authenticate the participants, or govern the relay provider’s role.

The boundary that matters is between transport and trust. A public relay moves packets or streams; it does not prove identity, authorize action, or guarantee confidentiality on its own. That distinction is often misunderstood when teams treat relay availability as evidence that the access design is “safe enough.” In practice, the relay is an infrastructure dependency that can affect latency, uptime, and troubleshooting, especially when the service sits outside the organisation’s own network perimeter.

Where the relay participates in machine access, session tooling, or remote administration, it can become part of an identity and access chain. For that reason, NHIMG treats relay design as an access-path decision, not merely a networking convenience.

Examples and Use Cases

Public relays appear in environments where direct connectivity is unreliable or intentionally restricted. They are most common when the goal is to preserve usability without forcing broad inbound exposure.

• Remote support tools use a public relay so a technician can connect to a host behind NAT without opening inbound ports.
• Peer-to-peer collaboration products fall back to relay mode when direct traversal fails, keeping the session alive at the cost of extra hops.
• Operational access to cloud-hosted or branch systems may route through a relay when private network paths are unavailable or inconsistent.
• Managed device and agent communications can depend on a relay for call-home traffic, especially in tightly segmented networks.
• Some session brokers use relays to simplify reachability across mobile, hybrid, or partner-managed networks where endpoint exposure must stay limited.

The trade-off is straightforward: broader reachability usually comes with more dependency on an external service and less control over traffic locality. That can be acceptable for short-lived sessions, but it is less attractive for sensitive or high-frequency control paths.

Security Implications

A public relay becomes security-relevant when organisations confuse connectivity with control. Because it sits in the middle of the access path, it can widen the blast radius of an outage, increase the number of parties involved in a session flow, and complicate assurance around where traffic is handled and how long metadata is retained.

Common failure modes include overreliance on the relay for reachability, weak segmentation around systems that depend on it, and poor visibility into whether the relay is carrying expected traffic or something abnormal. If the relay is compromised, misconfigured, or unavailable, operators may lose remote access to endpoints that only work through that path. If it is merely treated as a convenience layer, teams may miss the fact that it has become a critical dependency for administration, support, or agent communications.

For identity-heavy workflows, the relay can also obscure where authentication really happens. That matters because a session intermediary should never be assumed to confer trust. The secure question is not whether traffic can pass, but whether the access path remains observable, bounded, and recoverable.

Domain and Governance Relevance

In identity and access governance, a public relay is best understood as part of the access architecture that supports session establishment, not as the access decision itself. That matters when the relay is used for privileged administration, remote support, or non-human identity traffic, because the relay may become a hidden dependency in authentication and session routing.

When NHI or agentic systems use a relay to reach tools, APIs, or consoles, ownership becomes more important. The relay provider, the endpoint owner, and the identity owner may all influence the effective control boundary. If those responsibilities are unclear, organisations can end up with access paths that are operationally convenient but hard to audit, hard to retire, and hard to recover when something fails.

NHIMG’s view is that the governance question is not whether a relay is “good” or “bad.” It is whether the organisation can justify its use, observe its behaviour, and remove it when direct private connectivity becomes viable.

Related resources from NHI Mgmt Group

• Why do still-valid secrets matter after public disclosure?
• How should security teams reduce NTLM relay risk in Active Directory?
• When should organisations prioritise relay and coercion controls?
• How should security teams control public file sharing in Salesforce?