Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-08-31
2003-10-14
Robinson, Greta (Department: 2177)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395530, C707S793000, C707S793000
Reexamination Certificate
active
06633567
ABSTRACT:
BACKGROUND OF THE INVENTION
The first Ethernet LAN (“Local Area Network”) was implemented on a shared medium, such as a single co-axial cable connecting all devices in the LAN. The shared medium imposed a signal length restriction on the physical medium and a limit to the number of devices that could be connected to the LAN because only one device could transmit data at a time on the shared medium.
A switch provides a means of increasing the size of a LAN by providing a bridge between groups of devices connected on the same physical medium or LAN segment. The LAN can be viewed as multiple LAN segments connected together by one or more switches. For example, if a first port in the switch is connected to a first LAN segment and a second port in the switch is connected to a second LAN segment. The switch acts as a bridge between the LAN segments by forwarding data packets destined for a device connected to the second LAN segment from the first LAN segment.
Each device connected to the LAN segment in the LAN is assigned a unique Media Access Control (“MAC”) address. Each data packet includes a MAC source address assigned to the device transmitting the data packet and the MAC destination address of the device to which the data packet is to be forwarded.
The switch determines whether a data packet received on one LAN segment is to be forwarded on another LAN segment by associating a destination MAC address with a port in the switch; that port is connected to the LAN segment on which the MAC address resides. This association may be stored in a static forwarding entry in a forwarding table in the switch. A static forwarding entry is explicitly configured by management action and is not modified during the operation of the switch. For example, if device A is connected to LAN segment A and LAN segment A is connected to port
1
in the switch, a static forwarding entry for device A associates the MAC address for device A with port
1
. If device A is physically moved to segment B connected to port
2
in the switch, the static entry in the forwarding table for device A is not automatically updated to forward to port
2
instead of port
1
. A reconfiguration of the switch by management action is required to update a static forwarding entry.
The association between a MAC address and a port in the switch can be learned during operation of the switch instead of being explicitly configured in a static forwarding entry in the switch. Learning allows associations between MAC addresses and ports in the switch to be dynamically created and modified during operation of the switch. A learned association is stored in a dynamic forwarding entry in the forwarding table in the switch. In order to learn MAC addresses, the switch listens to data packets transmitted on all LAN segments connected to ports in the switch. The dynamic entry associates the MAC address with the port connected to the LAN segment from which a data packet is sourced.
The switch creates a new dynamic forwarding entry in the forwarding table upon detecting a MAC address stored in the source address field included in a data packet which does not have a corresponding forwarding entry in the forwarding table. The switch updates a dynamic forwarding entry associated with a MAC address each time it receives a data packet sourced from the MAC address.
For example, if the switch sees a data packet on segment A connected to port
1
with MAC address A stored in the source address field, the switch creates a dynamic forwarding entry in the forwarding table for MAC address A. The dynamic forwarding entry associates MAC address A with port
1
. Subsequent data packets received from another port in the switch including MAC address A as the destination address are forwarded through port
1
. If the device with MAC address A is moved to another LAN segment connected to port
2
in the switch, the switch learns the new association upon receiving a data packet on port
2
from MAC address A. The switch updates the dynamic forwarding entry for MAC address A to forward data packets to MAC address A through port
2
instead of port
1
.
Increasing the size of a LAN, by providing multiple LAN segments through the use of a switch, increases the bandwidth of the LAN and thus the number of devices that can be connected to the LAN. However, by increasing the number of devices connected to the LAN, the bandwidth consumed by broadcast traffic also increases. Broadcast traffic increases because upon receiving a data packet for an unknown MAC address, a broadcast packet is forwarded to all devices connected to the LAN in order to learn forwarding information for the unknown MAC address. The broadcast data packet includes a special MAC address sourced by one MAC address, which is forwarded to all other devices connected to the LAN. Unlike unicast traffic; that is, a data packet which is transmitted from a single source address to a single destination address, broadcast traffic cannot be limited to a single LAN segment. Thus, as the number of devices connected to a LAN increases, the amount of broadcast traffic increases, reducing the available bandwidth on the LAN regardless of the number of physical LAN segments in the LAN.
A solution for reducing broadcast traffic in a LAN is provided by logically segmenting the LAN into Virtual Local Area Networks (“VLAN”). A method for logically segmenting a LAN into VLANs is described in the Institute of Electric and Electronic Engineers (“IEEE”) P802.1Q standard. In a switch supporting VLANS a broadcast data packet is only forwarded through a port if the port is a member of same VLAN from which the data packet was received. Thus, broadcast traffic is only forwarded to devices which are members of the same VLAN on which the broadcast data packet was sourced.
In a LAN logically segmented into VLANs, each data packet forwarded on the LAN includes a VLAN Identifier (“VID”) identifying the VLAN from which the data packet was sourced. Membership of a VLAN is based on an assigned logical address, the VID, rather than a physical address. Thus, members of a VLAN need not be members of the same physical LAN segment. All traffic on the LAN, including broadcast, unicast and Multicast data traffic is restricted to the virtual VLAN on which it is sourced, by limiting the forwarding of traffic to members of the VLAN identified by the VID included in the data packet. A device can only communicate with a member of a VLAN if the device is also a member of the VLAN identified by the VID included in the received data packet. Thus, a VLAN contains broadcast traffic within the VLAN in which the broadcast packet is sourced and provides security for data transfer between members of the VLAN.
By applying VLANs to a LAN, a forwarding decision stored in a static forwarding entry or a dynamic forward entry is dependent on both the VID and the MAC address included in the received data packet. A MAC address may be a member of more than one VLAN requiring either a static or dynamic forwarding entry in the forward table for each VLAN in which the MAC address is a member. If the switch implements independent learning, a plurality of dynamic forwarding entries are provided for a MAC address, one for each VLAN in which the MAC address is learned.
In order to reduce the number of dynamic forwarding entries stored and updated for each learned MAC address, the switch may implement shared learning. Shared learning allows forwarding information learned for a MAC address on one VLAN to be shared by other VLANs in a given set of VLANs. The forwarding information is used for forwarding decisions taken for that MAC address.
To implement shared learning in a switch, each VLAN in the switch is associated with exactly one Filter Identifier (“FID”). For independent learning there is a one-to one correspondence between a VID and a FID. For shared learning, a plurality of VIDs are assigned to a FID. Only the VID is forwarded in a data packet, the FID is randomly assigned by the switch and used internally in the switch. In a shared learning switch all learned informatio
Hamilton, Brook, Smith and Reynolds, P.C.
Le Debbie M.
Mosaid Technologies Inc.
Robinson Greta
LandOfFree
Method and apparatus for searching a filtering database with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for searching a filtering database with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for searching a filtering database with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3171954