Virtual LANs over a DLSw network

Details Virtual LANs over a DLSw network Virtual LANs over a DLSw network

1999-06-10

2004-09-28

Chin, Wellington (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S401000

Reexamination Certificate

active

06798775

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to transfer of packets over a computer network, and more particularly to the use of a virtual local area network (VLAN) to address packets to a desired group of users throughout a wide area network.
BACKGROUND OF THE INVENTION
When a source computer transmits a packet onto a computer network, ordinarily the packet is transferred to every computer connected to the network as a potential destination computer. Each potential destination computer reads the destination address of the packet. In the event that the destination address indicates that the computer should receive the packet, the computer copies the packet into its memory and “receives” the packet, otherwise the computer ignores the packet.
Two levels of addressing are typically used in computer networks, the physical address and the Internet Protocol (IP) address. The physical address is usually assigned to a computer by the manufacturer, and is referred to as the “layer 2” address as it is recognized and used by source and destination computers at layer 2 of the Internet Protocol communications model. A synonym of “layer 2” address is the term “Media Access Address” (MAC address). The “layer 3” address is referred to as the Internet Protocol address (IP address), and it is used by “layer 3 procedures” of the Internet Protocol communications model.
During typical operation of a computer network, a packet is received by a computer based on its physical, or MAC, address. Computers connected to a computer network may be roughly categorized as “end stations”, a “layer 2 switch” or bridge, and a “layer 3 switch” or router. When the IP address is for the same computer as the MAC address, the computer is typically an end station and receives the packet. A layer 2 switch, or bridge, typically joins to small local area networks, typically referred to as “subnets”, and forwards the packet from a first subnet to a second subnet. A local area network is referred to as a “LAN” (plural, LANS).
A layer 3 switch, or router, receives a packet having the MAC address of the router and an IP address of a computer on a different subnet. The router, in response to the IP address in the layer 3 address field of the packet, routes the packet on its journey to the computer designated by the IP address of the packet. The router routes the packet from a source network to a destination network, in response to the IP address carried in the packet.
The MAC destination address field of a packet may indicate that the packet is addressed to a specific computer (unicast address), or may indicate that all computers on the network are designated to receive the packet (multicast address). Virtual Local Area Networks (VLANs) were introduced in order to provide a convenient way to have a selected group of computers receive a packet, in contrast to having only two choices of one computer or all computers receive the packet.
The VLAN construction, in an exemplary VLAN implementation, uses a router to define VLANs. A router typically has a plurality of ports, and each port may be connected to a different subnet, to a wide area network, to another router, etc. The VLAN implementation defines selected ports of a router to be members of a particular VLAN. The router then forwards a packet arriving on a port defined as a member of a particular VLAN onto all ports having the same VLAN designation, and onto no other ports. A plurality of routers may connect different subnets belonging to the same VLAN by having the ports of each router designated as ports for that particular VLAN. For example, VLANs implemented using Ethernet subnets typically are implemented by using selected ports of a router to define each VLAN. It is a common practice to use a “color” designation to specify a VLAN. Thus, certain ports of a router may be designated as the “red” VLAN ports, other ports the “blue” VLAN ports, still other ports the “green” VLAN ports, etc.
Another VLAN implementation is defined in IEEE Standard 802.1Q, (IEEE Draft Standard P802.1Q/D10, dated Mar. 22, 1998, all disclosures of which are incorporated herein by reference). Each packet carries a “tag” which identifies the packet as belonging to a VLAN. For example, a two byte field is defined as a “Tag Control Information” (TCI) format to carry VLAN, priority, and “canonical” information. The VLAN identification is 12 bits and is referred to as the “VID” field. The priority field is 3 bits, and so can represent 8 priority layers, from 0 to 7. The “canonical” indicator is 1 bit and designates the method of ordering the significant bits in the fields (canonical or noncanonical). The canonical indicator is referred to herein as the “CFI” tag, or CFI tag field. The structure of the Tag Header is more fully described in Clause 9.3 of IEEE 802.1Q, especially for different types of frames, Ethernet, SNAP SAP encoded, etc.
Secure Data Exchange (SDE) is defined in the IEEE Standard 802.10 (IEEE Standard 802-10-1998, Approved 17 Sep. 1998, all disclosures of which are incorporated herein by reference). An SDE designator field in a packet occupies the first three octets in the LLC header, and a SDE packet has the values 0A0A03 in the SDE designator field. Non SDE entities, including stations, bridges, routers, etc., ignore a packet having a SDE designator. Accordingly, a SDE packet is transmitted by a computer which writes an SDE designator field, and is received by only those computers which interpret the SDE designator field. Therefore, packets with an SDE designator field behave much as do packets with a virtual local area network identification assignment, in that the SDE designator is equivalent to a VLAN ID.
Further, VLAN identification is included in an encapsulating header, for example, an encapsulating header for Ethernet packets. The ISL format of Cisco Systems, Inc. provides a 12 bit VLAN identification in an encapsulating header for Ethernet packets, as set out in the document “
Configuring Routing between VLANs with ISL Encapsulation
”, available on the Web page at www.cisco.com maintained by Cisco Systems, Inc., all disclosures of which are incorporated herein by reference.
VLANs are widely used today in communications using Ethernet (IEEE 802.3) LANs. Particularly, a VLAN may be implemented on geographically separated Ethernet LANs by the ISL format of Cisco Systems, Inc. used to provide a trunk connection between the two geographically separated Ethernet LANs. The “trunk” connection is logically many VLANs sharing the same communications path. An example of geographically separated Ethernet LANs may be one LAN in New York City and the other in San Francisco, with a VLAN capable media connection between the two LANs implementing VLAN format. The IEEE 802.1Q standard protocol is similar to the Cisco Systems, Inc. ISL format and may also be used to join geographically separated LANs into a VLAN with tagged packets. The advantage of using the VLAN format is that only those computers receiving a particular tag, for example, red, or blue, or green, etc., will receive the tagged packets, and thereby reduces the number of computers receiving the tagged packets.
Data Link Switching (DLSw) is defined in RFC 1795 (Internet Engineering Task Force, Request for Comments 1795, April 1995, all disclosures of which are incorporated herein by reference) as a means for interconnecting a first network served by a first router to a second network served by a second router by operating a TCP/IP connection between the two routers. An encapsulating protocol referred to as Switch to Switch (SSP) protocol encapsulates the packets received from the networks before transmission over the TCP/IP connection, as set out in RFC 1795. These two routers are referred to as the “DLSw routers” because a port of each is used to establish the DLSw connection between the two networks. In a widely used configuration, both the first network and the second network are source routed networks such as an IEEE 802.5 Source Route Bridge (SRB) network. Accordingly, the first and second networks comprise IEEE 802.5 token

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