|
|
LAN Emulation (LANE) provides connectivity between ATM-attached devices and LAN-attached devices, including the following:
Because LANE connectivity is defined at the MAC layer, upper protocol layer functions of LAN applications can continue unchanged when the devices join ATM VLANs.
An ATM network can support multiple independent ATM VLANs. End-system membership in any of the ATM VLANs is independent of the physical location of the end system, which simplifies hardware moves and changes. In addition, the end systems can move easily from one ATM VLAN to another, whether or not the hardware moves. Figure A-1 shows an ATM LANE configuration.
Communication among LANE components is ordinarily handled by several types of switched virtual channel connections (VCCs). Some VCCs are unidirectional; others are bidirectional. Some are point-to-point, and others are point-to-multipoint. Figure A-2 illustrates the various types of VCCs.
A VLAN is a logical group of end stations, independent of physical location, with a common set of requirements. Currently, the Catalyst switches support a port-centric VLAN configuration. All end stations connected to ports belong to the same VLAN and are assigned to the same VLAN number. The VLAN number is only significant to the Catalyst switch.
On an ATM network, a VLAN is called an ATM VLAN and is designated by a name. You can configure some ATM VLANs from a router and some from a Catalyst switch. You can configure some ATM VLANs with unrestricted membership and some with restricted membership. You can also configure a default ATM VLAN, which must have unrestricted membership.
The following process (illustrated in Figure A-2) normally occurs after a client has been enabled on the ATM module in a Catalyst switch:
The client sets up a connection to the configuration server (bidirectional, point-to-point Configure Direct VCC, link 1-7 in Figure A-2) to find the ATM address of the LE server for its ATM VLAN.
The clients find the configuration server by using the following interface and addresses in the listed order:
a. Locally configured ATM address
b. ILMI
c. Fixed address defined by the ATM Forum
The LE server for the ATM VLAN sets up a connection to the configuration server to verify that the client is allowed to join the ATM VLAN (bidirectional, point-to-point Server Configure VCC, link 11-12 in Figure A-2). The LE server configuration request contains the client MAC address, its ATM address, and the name of the ATM VLAN. The configuration server checks its database to determine whether the client can join that LAN; then it uses the same VCC to inform the LE server whether or not the client is allowed to join.
As communication occurs on the ATM VLAN, each client dynamically builds a local LANE Address Resolution Protocol (LE ARP) table. A client LE ARP table can also have static, preconfigured entries. The LE ARP table maps MAC addresses to ATM addresses.
When a client first joins an ATM VLAN, its LE ARP table has no dynamic entries, and the client has no information about destinations on or behind its ATM VLAN. To learn about a destination when a packet is to be sent, the client begins the following process to find the ATM address corresponding to the known MAC address:
For unknown destinations, the client sends a packet to the broadcast server, which forwards the packet to all clients. The broadcast server floods the packet because the destination might be behind a bridge that has not yet learned this particular address.
When a client sends broadcast, multicast, or unicast traffic with an unknown address, the following process occurs:
On a LAN, packets are addressed by the MAC-layer addresses of the destination and source stations. To provide similar functionality for LANE, MAC-layer addressing must be supported. Every client must have a MAC address. In addition, every LANE component (configuration server, LE server, broadcast server, and client) must have a unique ATM address.
In this release, all clients on the same interface have the same automatically assigned MAC address. That MAC address is also used as the end-system identifier (ESI) part of the ATM address, as explained in the following section. Although client MAC addresses are not unique, all ATM addresses are unique.
A LANE ATM address has the same syntax as an NSAP, but it is not a network-level address. It consists of the following:
Cisco provides the following method of constructing and assigning ATM and MAC addresses in an configuration server database. A pool of MAC addresses is assigned to each ATM module. The pool contains 16 MAC addresses. For constructing ATM addresses, the following assignments are made to the LANE components:
Because the LANE components are defined on different subinterfaces of an ATM interface, the value of the selector field in an ATM address is different for each component. The result is a unique ATM address for each LANE component, even within the same Catalyst switch. For more information about assigning components to subinterfaces, see the "Assigning Components to Interfaces and Subinterfaces" section.
For example, if the MAC addresses assigned to an interface are 0800.200C.1000 through 0800.200C.100F, the ESI part of the ATM addresses is assigned to LANE components as follows:
You can use ATM address templates in many LANE commands. These templates can assign ATM addresses to LANE components (thus overriding automatically assigned ATM addresses) or link client ATM addresses to ATM VLANs, simplifying the use of LANE commands. ATM address templates are very similar to the address templates used by the International Standards Organization (ISO) connectionless network services (CLNS).
LANE ATM address templates can use two types of wildcards: an asterisk (*) to match any single character and an ellipsis (...) to match any number of leading or trailing characters.
In LANE, a prefix template explicitly matches the prefix but uses wildcards for the ESI and selector fields. An ESI template explicitly matches the ESI field but uses wildcards for the prefix and selector. Table A-1 indicates how the values of unspecified bytes are determined when an ATM address template is used.
| Unspecified Digits | Value Location |
|---|---|
| Prefix (first 13 bytes) | Switch via ILMI, or configured locally if ILMI is not supported on the switch. |
| ESI (next 6 bytes) | Slot MAC address1 plus one of the following
|
|
Selector field (last byte) | Subinterface number, in the range 0 through 255. |
The following rules apply to assigning LANE components on the major ATM interface and its subinterfaces:
The Catalyst switch builds its ATM address by obtaining its ATM address prefix from the ATM switch. Then it combines the ATM address prefix with its own MAC address and the client subinterface number. Once the Catalyst ATM module has determined its ATM address, it uses ILMI registration to register this address with the ATM switch.
Using the atm vc-per-vp command, you can configure the maximum number of virtual channel identifiers (VCIs) per virtual path identifier (VPI). If this value is configured when the Catalyst switch ATM module registers with the ATM switch, the maximum number of VCIs per VPI is passed to the ATM switch. In this way, the ATM switch assigns to the Catalyst switch a VCI value for a switched virtual circuit (SVC) that is within the ATM switch range. The default is 10 VCI bits, and 2 VPI bits on the Catalyst ATM module. Any change from the default requires an ATM module reset.
|
|