Configuration Concepts

Configuration Concepts

There are several important concepts used in configuring LANE on Cisco devices, including the following:

  • Mapping VLAN numbers to ELAN names
  • Addressing
  • Subinterfaces

Mapping VLAN Numbers to ELAN Names

Whereas the Catalyst refers to broadcast domains with VLAN numbers, LANE always uses textual ELAN names. The LEC is used to map the VLAN number into an ELAN name (as is discussed in the “Configuration Syntax” section later, this mapping is established via the command that creates the Client). ELAN names can be up to 32 characters in length. Be very careful when configuring ELAN names because they are case sensitive.

Subinterfaces

As explained in Chapter 8, “Trunking Technologies and Applications,” Cisco uses the subinterface concept to create logical partitions on a single physical interface. In this case, each partition is used for a separate ELAN as shown in Figure 9-25.

Figure 9-25. Each Subinterface Is Used for a Separate ELAN
configuration-concepts-9.25

In Figure 9-25, subinterface ATM 0.1 is used for ELAN1, and ATM 0.2 is used for ELAN2. Cat-A is a client on both ELANs and therefore requires a LEC on both subinterfaces. Because Cat-A is also acting as the LES and BUS for ELAN2 (but not ELAN1), these services are only configured on subinterface ATM 0.2. However, notice that the LECS is configured on the major interface, ATM 0. This placement mirrors the roles that each component plays:

  • Because the LECS doesn’t belong to any particular ELAN, it is placed on the major interface. As a global concept, the LECS should be placed on the global interface.
  • LECs, LESs, and BUSs that do belong to specific ELANs are placed on subinterfaces.

In short, subinterfaces allow the interface configuration to match the LANE configuration.

  • Tip
    Although most LANE components are configured on a subinterface, the LECS is always configured on the major interface of Cisco equipment.

Addressing

LANE’s reliance on SVCs requires careful planning of NSAP addresses (recall that SCVs are built by placing an ATM phone call to an NSAP address). Although Cisco allows you to manually configure NSAP addresses, an automatic NSAP addressing scheme is provided to allow almost plug-and-play operation.

Recall from Figure 9-6 that NSAP addresses have three sections:

  • A 13-byte prefix from the ATM switch (LS1010)
  • A 6-byte ESI from the edge device (Catalyst LANE module)
  • A 1-byte selector byte from the edge device (Catalyst LANE module)

The LANE components automatically acquire the prefix from the ATM switch. However, what does the Catalyst provide for the ESI and selector byte values? Cisco has created a simple scheme based on MAC addresses to fulfill this need. Every ATM interface sold by Cisco has a block of at least eight MAC addresses on it (some interfaces have more). This allows each LANE component to automatically adopt a unique NSAP address using the pattern shown in Table 9-3.

Table 9-3. Automatic ESI and Selector Byte Values

LANE Component ESI Selector Byte
LEC MAC Address .**
LES MAC Address + 1 .**
BUS MAC Address + 2 .**
LECS MAC Address + 3 .00
** Represents the subinterface where a LANE component is created

For example, assume that an ATM switch is using a prefix of 47.0091.8100.0000.0060.1234.5678 and the first MAC address on a LANE blade is 0000.0CAB.5910. If you build all four components on this device and use subinterface ATM 0.29, Table 9-4 shows the resulting NSAP addresses.

Table 9-4. Sample NSAP addresses

LANE Component NSAP
LEC 47.0091.8100.0000.0060.1234.5678.0000.0CAB.5910.1D
LES 47.0091.8100.0000.0060.1234.5678.0000.0CAB.5911.1D
BUS 47.0091.8100.0000.0060.1234.5678.0000.0CAB.5912.1D
LECS 47.0091.8100.0000.0060.1234.5678.0000.0CAB.5913.00

As discussed earlier, notice that the LECS always appears on the major interface and uses .00 as a selector byte. Also note that although subinterfaces are expressed in decimal to the IOS (interface ATM 0.29), the selector byte is expressed in hexadecimal (0x1D).

  • Tip
    Although subinterface numbers are expressed in decimal in the IOS configuration, they are expressed in hex when used for the ATM NSAP’s selector byte.

In practice, Cisco makes it extremely easy to determine the NSAP addresses for a specific Catalyst LANE module—just use the show lane default command. For example, the Catalyst output in Example 9-1 is connected to an ATM switch with the prefix 47.0091.8100.0000.0010.2962.E801.

Example 9-1 Determining NSAP Addresses for a Catalyst LANE Module

The selector byte is shown as .** for the LEC, LES, and BUS because the subinterface numbers are not revealed by this command.

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