IPv6 multihomed link-local and site-local support
A host can have more than one interface defined. A host with two or more active interfaces is called multihomed. Each interface has a link-local address associated with it.
Link-local addresses are sufficient for allowing communication among nodes attached to the same link.
A multihomed host has two or more associated link-local addresses. The AIX IPv6 implementation has 4 options to handle how link-layer address resolution is resolved on multihomed hosts. Option 1 is the default.
| Item | Description |
|---|---|
| Option 0 | No multihomed actions are taken. Transmissions will go out on the first link-local interface. When the Neighbor Discovery Protocol (NDP) must perform address resolution, it multicasts a Neighbor Solicitation message out on each interface with a link local address defined. NDP queues the data packet until the first Neighbor Advertisement message is received. The data packet is then sent out on this link. |
| Option 1 | When the NDP must perform address resolution, that is, when sending a data packet to a destination and the link-layer information for the next hop is not in the Neighbor Cache, it multicasts a Neighbor Solicitation message out on each interface with a link-local address defined. NDP then queues the data packet until it gets the link-layer information. NDP then waits until a response is received for each interface. This guarantees that the data packets are sent on the appropriate outgoing interfaces. If NDP did not wait, but responded to the first Neighbor Advertisement received, it would be possible for a data packet to be sent out on a link not associated with the packet source address. Because NDP must wait, a delay in the first packet being sent occurs. However, the delay occurs anyway in waiting for the first response. |
| Option 2 | Multihomed operation is allowed, but dispatching of a data packet is limited to the interface specified by main_if6. When the NDP must perform address resolution, it multicasts a Neighbor Solicitation message out on each interface with a link-local address defined. It then waits for a Neighbor Advertisement message from the interface specified by main_if6 (see the no command). Upon receiving a response from this interface, the data packet is sent out on this link. |
| Option 3 | Multihomed operation is allowed, but dispatching of a data packet is limited to the interface specified by main_if6 and site-local addresses are only routed for the interface specified by main_site6 (see the no command). The NDP operates just as it does for Option 2. For applications that route data packets using site-local addresses on a multihomed host, only the site-local address specified by main_site6 are used. |