Route filtering with Via

Via introduces routing awareness to grants by letting you include a via field to specify how Tailscale can route the destination (dst) from the source (src).

You can use the via syntax to define the exit nodes, subnet routers, or app connectors a source can access when they use a specific destination. For example, you can create a grant that forces traffic through a specific exit node when it goes from the engineering team group to the GitHub app connector.

Using the via field in grants lets you do things like:

• Route traffic to an enterprise application through a specific exit node.
• Route traffic from devices through different exit nodes based on whether they meet device posture criteria.
• Route traffic from specific users through a subnet router.

Limitations

• You can only use tags within the via field.
• For failover and regional routing reasons, you can only use accessible routers as via candidates. The routers accessible to users depends on applicable access policies.

Syntax

Via is an extension of the grant syntax. It adds a single field, via, that you can use to specify how the source routes to the destination. The following example shows how to use the via field.

"grants": [
    {
        "src": ["<source>"],
        "dst": ["<destination>"],
        "via": ["tag:<tag-name>"],
        "ip": ["*"]
    },
]

This example ensures traffic from <source> to <destination> goes through a device with the tag <tag-name>.

Examples

The following examples illustrate using the via field in grants for common use cases.

• Route traffic based on device posture rules.
• Route users through exit nodes based on location.
• Route users through app connectors.

Route traffic based on device posture rules

You can use the via field to segment access to resources through different routers based on device posture management rules.

The following example demonstrates a scenario in which the engineering team group can access a 192.0.2.0/24 using any available router if they comply with the latestMac posture (which ensures they are running the latest stable version of the Tailscale client for macOS). Anyone else (autogroup:member) can access 192.0.2.0/24 using the designated office router (tag:office-router).

"postures": {
    "posture:latestMac": [
        "node:os == 'macos'",
        "node:osVersion == '13.4.0'",
        "node:tsReleaseTrack == 'stable'",
    ]
},
"grants": [
    {
        "src": ["group:eng"],
        "srcPosture": ["posture:latestMac"],
        "dst": ["192.0.2.0/24"],
        "ip": ["*"],
    },
    {
        "src": ["autogroup:member"],
        "dst": ["192.0.2.0/24"],
        "via": ["tag:office-router"],
        "ip": ["*"],
    },
]

Route users through exit nodes based on location

You can use the via field to segment different exit nodes to different users.

The following example demonstrates a scenario where users can access internet resources through an exit node based on the user's home office location.

Users in the Toronto (group:tor) and Seattle (group:sea) offices can access internet resources using exit nodes near their home offices (or directly from their device when exit nodes are not selected). Users on the engineering team (group:eng) can access internet resources using any exit node in the tailnet (or directly from their device when exit nodes are not selected).

"grants": [
    {
        "src": ["group:tor"],
        "dst": ["autogroup:internet"],
        "via": ["tag:exit-node-tor"],
        "ip": ["*"],
    },
    {
        "src": ["group:sea"],
        "dst": ["autogroup:internet"],
        "via": ["tag:exit-node-sea"],
        "ip": ["*"],
    },
    {
        "src": ["group:eng"],
        "dst": ["autogroup:internet"],
        "ip": ["*"],
    },
]

Route users through app connectors

You can use the via field to segment different app connectors to different users.

The following example demonstrates a scenario in which users in the group group:github-users can access GitHub through an app connector tagged tag:github-appconnector while users in the group group:salesforce-users can access Salesforce through an app connector tagged tag:salesforce-appconnector.

"grants": [
    {
        "src": ["group:github-users"],
        "dst": ["autogroup:internet"],
        "ip":  ["*"],
        "via": ["tag:github-appconnector"],
    },
    {
        "src": ["group:salesforce-users"],
        "dst": ["autogroup:internet"],
        "ip":  ["*"],
        "via": ["tag:salesforce-appconnector"],
    }
]