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Summary

When a dynamic network configuration is desired and a local DHCP server is not available for a network, Ubuntu needs to correctly assign itself a link-local address. This is implemented by avahi-autoipd, but requires some additional configuration and packaging corrections to have the system behave in a fully correct way.

Rationale

Other operating system correctly use link-local addresses for communicating on adhoc networks or local LANs without a DHCP server. Ubuntu users will be much happier and more productive when they are effortlessly able to communicate with other device with link-local addresses.

Use cases

  1. Claudia and Mary set up an adhoc wireless network between between their laptops. They want to be able to communicate without needing to do anything special with interface address assignments.
  2. John's home server was booted and it got a link-local address. He adds a DHCP server to his network, and boots his laptop, which receives a regular DHCP-assigned address. He wants his server and laptop to be able to communicate without fiddling with their interfaces.

  3. Ellen uses a name server that makes a .local top-level-domain available. She upgrades her computer from Edgy to Feisty, where link-local addresses are assigned by default. She gets a notification that the unicast .local TLD and the link-local .local domain conflict with each other, along with instructions on how to disable link-local networking.

Scope

Up to version 6.10, Ubuntu did not create or use link-local addresses by default. Changes to implement this spec will be limited to making this functionality available without impacting the existing dynamic and static network assignments methods. The work will mostly surround avahi-autoipd and libnss-mdns, with supporting changes in related packages. Changes to, or enhancements of, DNS service-discovery are out of scope for this spec.

Design

Implementation

Clarification of terminology

Zeroconf is a collection of protocols including ipv4 link local networking, mDNS, and DNS service-discovery. Apple's implementation of zeroconf was originally named "Rendezvous" and was later renamed to "Bonjour". Avahi is a free software implementation of zeroconf. See http://avahi.org/wiki/AboutAvahi.

Comments

Tests

  1. Create a small network between computers that does not involve a DHCP server, by doing one of:
    • plug two computers together with a crossover ethernet cable and tell network-manager to use the cable network; after about 30 seconds it should display that it is connected to the cable network

    • use network-manager to create an ad-hoc WLAN and connect to it using another computer with a WiFi card; after about 30 seconds, that other computer should connect to the wifi as well. (The 30 seconds is the default DHCP waiting timeout)

      Now check with ifconfig that there is an ethX:avahi interface on either side with a 169.254.x.x address.

  2. Use ping hostname.local (where hostname is the name of the remote computer) to check that you can ping each other using nss-mdns. You should also be able to ping your own hostname, of course (with .local appended).

  3. Call route and verify that there is a route to the link-local network target (as opposed to only displaying the numerical 169.254.0.0 value).

  4. Manual configuration: Choose 'static configuration' in network-manager (which brings up network-admin). Select an interface, click 'Properties' and change it to Local zeroconf network (IPv4LL). This should change the method in /etc/network/interfaces to ipv4ll. Enabling the device in network-admin (or with sudo ifup ethX) should configure the ethX:avahi interface immediately. (Note that this method is really only for users who know what they are doing).

CategorySpec

ZeroConfNetworking (last edited 2008-08-06 17:00:50 by localhost)