Michael Stapelberg
129 lines
4.1 KiB
Markdown
129 lines
4.1 KiB
Markdown
---
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title: "DHCP Client"
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menuTitle: "DHCP Client"
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weight: 21
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---
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Each gokrazy instance comes with a built-in DHCP client (see [Instance Config →
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GokrazyPackages](/userguide/instance-config/#gokrazypackages) for more details
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on system packages) to set the IP address after obtaining a
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[DHCPv4](https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol)
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lease from the local network’s DHCP server.
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## Network Interfaces
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The gokrazy DHCP client by default runs for `eth0`. If you want to use a
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different network interface, perhaps a USB ethernet adapter, you can set the
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`-interface` [command-line flag](/userguide/package-config/):
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{{< highlight json "hl_lines=10-14" >}}
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{
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"Hostname": "dynamic",
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"Packages": [
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"github.com/gokrazy/fbstatus",
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"github.com/gokrazy/hello",
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"github.com/gokrazy/serial-busybox",
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"github.com/gokrazy/breakglass",
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],
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"PackageConfig": {
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"github.com/gokrazy/gokrazy/cmd/dhcp": {
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"CommandLineFlags": [
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"-interface=enp0s58"
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]
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}
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}
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}
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{{< /highlight >}}
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If you configure gokrazy to [connect to a WiFi network](/userguide/wifi/), the
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`gokrazy/wifi` package will [run another
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instance](https://github.com/gokrazy/wifi/blob/320785ba3e91dac849e28d888c1cf6e6568320d0/wifi.go#L83)
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of the gokrazy DHCP client with the `-interface=wlan0` flag set.
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## Static Network Configuration
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If you want the DHCP client to not actually fetch a lease, but apply a
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statically supplied network configuration instead, you can set the
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`-static_network_config` flag to the name of a file which contains a
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JSON-encoded [DHCP lease in `rtr7/dhcp4.Lease`
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format](https://github.com/rtr7/dhcp4/blob/18c84d089b4648dc5ea2ffe30efa65dfcb8a31ca/parseopts.go#L167), for example:
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```json
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{
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"IP": "192.168.178.2",
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"Netmask": "",
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"Router": "192.168.178.1",
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"DNS": ["192.168.178.1", "8.8.8.8"]
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}
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```
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Specifically, the following fields are currently respected:
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* IP+Netmask
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* Router
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* DNS
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You can configure the gokrazy DHCP client to pick up this configuration by
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setting [Package config: Command-line flags](/userguide/package-config/#flags)
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and [Package config: Extra files](/userguide/package-config/#extrafiles):
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{{< highlight json "hl_lines=10-17" >}}
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{
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"Hostname": "dynamic",
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"Packages": [
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"github.com/gokrazy/fbstatus",
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"github.com/gokrazy/hello",
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"github.com/gokrazy/serial-busybox",
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"github.com/gokrazy/breakglass"
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],
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"PackageConfig": {
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"github.com/gokrazy/gokrazy/cmd/dhcp": {
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"CommandLineFlags": [
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"-static_network_config=/etc/gokrazy/static-dhcp-lease.json"
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],
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"ExtraFilePaths": {
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"/etc/gokrazy/static-dhcp-lease.json": "static-dhcp-lease.json"
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}
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}
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}
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}
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{{< /highlight >}}
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## Interface priority
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The gokrazy DHCP client [automatically configures the route
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priority](https://github.com/gokrazy/gokrazy/commit/4c375187675fd3c3f2fb1381be87b7d046dd1f42)
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for default routes of ethernet interfaces (`eth*`) to 1, whereas on WiFi
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interfaces (`wlan*`), the priority is 5 (Linux prefers lower priorities).
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This means you can configure your gokrazy instance to work with both, WiFi and
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wired network. Whenever a link is down, the gokrazy DHCP client changes its
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priority to 1024, meaning outgoing traffic will quickly switch away when an
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interface loses its link. In other words: When you un-plug the network cable,
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the device still works via WiFi.
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If you need to influence the interface’s route priority, you can use the
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`-extra_route_priority` flag to add to the default priority. For example, to
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prefer sending traffic out via the WiFi interface if both WiFi and ethernet are
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connected, use:
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{{< highlight json "hl_lines=10-14" >}}
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{
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"Hostname": "dynamic",
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"Packages": [
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"github.com/gokrazy/fbstatus",
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"github.com/gokrazy/hello",
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"github.com/gokrazy/serial-busybox",
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"github.com/gokrazy/breakglass",
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],
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"PackageConfig": {
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"github.com/gokrazy/gokrazy/cmd/dhcp": {
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"CommandLineFlags": [
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"-extra_route_priority=10"
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]
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}
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}
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}
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{{< /highlight >}}
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