Configuring interfaces using IPv6

All interfaces used in normal IP routing must be set up with a unicast address to receive unicasted traffic. In IPv6 there are several classes of unicast addresses. The different classes are:

• Link-Local addresses - These are used during auto-configuration and when no routers are present. Link Local addresses are valid only on the link of an interface. This means that traffic destined for such addresses is never routed.

• Site Local addresses - These are similar to the private IPv4 addresses, with the added advantage that everyone who uses this capability is given the ability to use the given 16 bits for a maximum of 65536 subnets. Also, because you can assign more than one ip to an interface, you can communicate on your private LAN and the Internet simultaneously without any special routing or NAT translations.

• Global unicast addresses - These are public (Internet) IP addresses. All subfields in global addresses are variable-length, non-self-encoding.

Since interfaces often are configured with multiple IPv6 addresses from both the site local and global address space, there is the question of what address olsrd should use for the interface. The address-type to use can be set in the configuration file using the IP6ADDRTYPE statement. By default it is set to use site local addresses since a MANET often is seen as a private network. However, if Internet connectivity is desired one needs to use global addresses or one must use some address translation scheme in the Internet gateways. Optionally, a node could send all its site-local and global addresses in MID messages to ensure that all of its addresses are route-able.

In olsrd, configuration of interfaces is done different when using IPv6 from IPv4. While IPv4 configuration uses ioctl calls, IPv6 operation reads all info from the proc file /proc/net/if_inet6. This file lists all configured IPv6 addresses and the interfaces they are configured to. This way a network interface can have multiple entries in the file, one for each configured IPv6 address. Each entry includes information about the address type as well. When fetching interface information, this proc file is parsed and the first located address of the correct type for the specific network interface is used. If no address of the desired class is located for a network interface, then that network interface will not be set up for use by olsrd.