Private Networking

Use network.private_hosts when a browser session joins a VPN or tunnel and must reach private services through that connection. Matching destinations bypass Kernel-managed egress and use the session’s network routes and DNS instead. This is useful for services reachable through Tailscale, a corporate VPN, or another tunnel running inside the browser session.

network.private_hosts is different from network.proxy_routes, which sends selected hosts through a chosen proxy, and a proxy’s bypass_hosts, which chooses between that proxy and Kernel-managed direct egress. Private hosts bypass Kernel-managed egress so traffic can follow routes inside the browser session, including VPN and tunnel routes.

Configure a browser

Set private hosts when you create the browser. You can’t change them after creation.

import Kernel from '@onkernel/sdk';

const kernel = new Kernel();

const browser = await kernel.browsers.create({
  network: {
    private_hosts: [
      '*.services.example.ts.net',
      '100.64.0.0/10',
    ],
  },
});

console.log(browser.session_id);

from kernel import Kernel

kernel = Kernel()

browser = kernel.browsers.create(
    network={
        "private_hosts": [
            "*.services.example.ts.net",
            "100.64.0.0/10",
        ]
    }
)

print(browser.session_id)

package main

import (
    "context"
    "fmt"

    "github.com/kernel/kernel-go-sdk"
)

func main() {
    client := kernel.NewClient()

    browser, err := client.Browsers.New(context.Background(), kernel.BrowserNewParams{
        Network: kernel.BrowserNetworkConfigParam{
            PrivateHosts: []string{
                "*.services.example.ts.net",
                "100.64.0.0/10",
            },
        },
    })
    if err != nil {
        panic(err)
    }

    fmt.Println(browser.SessionID)
}

kernel browsers create \
  --private-host '*.services.example.ts.net' \
  --private-host '100.64.0.0/10'

Default private routes

When you omit network.private_hosts, Kernel routes these private IP ranges through the session network by default:

RFC1918: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16
CGNAT and Tailscale: 100.64.0.0/10
IPv6 unique local addresses: fc00::/7

These CIDR rules only match URLs that use literal IP addresses. They don’t match a hostname after DNS resolution. Add private DNS names explicitly, even when they resolve to an address in a default range:

{
  "network": {
    "private_hosts": ["api.services.example.ts.net"]
  }
}

Providing private_hosts replaces the default list; it doesn’t add to it. Include any default CIDRs you still need alongside your hostname rules.

To disable direct private routing for browser requests and send them through Kernel-managed egress, provide an explicit empty list:

const browser = await kernel.browsers.create({
  network: { private_hosts: [] },
});

browser = kernel.browsers.create(
    network={"private_hosts": []}
)

Supported entries

You can provide up to 32 entries, each no longer than 255 characters:

Exact hostnames: api.services.example.ts.net
A single leading wildcard: *.services.example.ts.net
Private IPv4 addresses: 10.1.30.63
Bracketed private IPv6 addresses: [fd00::1]
Canonical private CIDRs: 100.64.0.0/10 or fd00::/8
Hostnames or exact IP addresses with ports: api.services.example.ts.net:8443

Kernel rejects public IP ranges, loopback and link-local ranges, URL schemes, paths, catch-all wildcards, ports on CIDRs, and non-canonical CIDRs. Hostnames aren’t resolved during validation, so only add names that identify private destinations.

Configure a browser pool

Put the network configuration on a browser pool when every browser in the pool needs the same private routes.

const pool = await kernel.browserPools.create({
  name: 'private-services',
  size: 5,
  network: {
    private_hosts: ['*.services.example.ts.net'],
  },
});

pool = kernel.browser_pools.create(
    name="private-services",
    size=5,
    network={
        "private_hosts": ["*.services.example.ts.net"],
    },
)

kernel browser-pools create private-services \
  --size 5 \
  --private-host '*.services.example.ts.net'

Changes to a browser pool’s private_hosts apply only to browsers created after the update. Pass discard_all_idle: true in an SDK request, or --discard-all-idle in the CLI, to immediately replace idle browsers with the new configuration. Acquired browsers keep their original private-host configuration until you release them with reuse disabled. Egress allowlist updates follow different replacement and release rules. Use kernel browser-pools update private-services --clear-private-hosts --discard-all-idle to remove a pool override and restore the default private IP ranges. To configure an explicit empty list, use an SDK request with network.private_hosts: [].

Overview

Start building

How it works

Partnering with KERNEL

Private Networking

Configure a browser

Default private routes

Supported entries

Configure a browser pool

​Configure a browser

​Default private routes

​Supported entries

​Configure a browser pool

Configure a browser

Default private routes

Supported entries

Configure a browser pool