Chapter 7. Subnet-Local Addressing

The Previous Chapter

The previous chapter provided an introduction to the layers comprising the IBA stack that handles message transmission and reception. Those layers are:

• The ULP (Upper Layer Protocol). This is actually not part of the IBA stack. Rather, it is comprised of OS and application software that uses the stack to pass messages.

• The Verb Layer.

• The Transport Layer.

• The Network Layer.

• The Link Layer.

• The Physical Layer.

This Chapter

This chapter defines the addresses that are used to route a packet from its source port to its destination port within an IBA subnet. It defines how ports on CAs, switches, and routers are numbered. It then defines the Local ID (LID) address space, the purpose of the LID address, and the SM's assignment of a unique LID to each port. The SM may optionally assign a range of LID addresses to a port. This chapter defines how this is done as well as the value of assigning more than one address to a port. It describes how the QP indicates which of the local port's assigned LID addresses will be inserted into the LRH:SLID field when the QP sources a packet to the port for transmission. The concept of the SM's path database is introduced.

The Next Chapter

The next chapter describes the 128-bit global address used to route a packet from its source CA port in one subnet to the destination CA port in another subnet. IPv6 (Internet Protocol version 6) addresses are introduced (both unicast and multicast) as well as the documentation convention used for IPv6 addresses. Each 128-bit global address consists of a 64-bit subnet prefix and a 64-bit globally unique ID (GUID). This chapter describes how each port in a subnet is assigned the same subnet ID as well as one or more GUIDs. The concept of a global multipathing is introduced.