3.2 LINK/INTERNET LAYER INTERFACE

This document does not attempt to specify the interface between the Link Layer and the upper layers. However, note well that other parts of this document, particularly chapter 5, require various sorts of information to be passed across this layer boundary.

This section uses the following definitions:

• Source physical address

  The source physical address is the Link Layer address of the host or router from which the packet was received.

• Destination physical address The destination physical address is the Link Layer address to which the packet was sent.

The information that must pass from the Link Layer to the Internetwork Layer for each received packet is:

1. The IP packet [5.2.2],

2. The length of the data portion (i.e., not including the Link- Layer framing) of the Link Layer frame [5.2.2],

3. The identity of the physical interface from which the IP packet was received [5.2.3], and

4. The classification of the packet's destination physical address as a Link Layer unicast, broadcast, or multicast [4.3.2], [5.3.4].

   In addition, the Link Layer also should provide:

5. The source physical address.

The information that must pass from the Internetwork Layer to the Link Layer for each transmitted packet is:

1. The IP packet [5.2.1]

2. The length of the IP packet [5.2.1]

3. The destination physical interface [5.2.1]

4. The next hop IP address [5.2.1]

   In addition, the Internetwork Layer also should provide:

5. The Link Layer priority value [5.3.3.2]

The Link Layer must also notify the Internetwork Layer if the packet to be transmitted causes a Link Layer precedence-related error [5.3.3.3].