Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-08-11
2001-07-03
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S424000, C709S220000, C709S238000
Reexamination Certificate
active
06256314
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to networks and apparatus and methods for switching in networks.
BACKGROUND OF THE INVENTION
Local area networks (LANs) and IP networking are well known in the art. LANs and IP networking in general and in particular relevant aspects of IP routing and ARP are described in the following publications:
International Standard for MAC Bridging: Std 802.1D, IEEE, 1993,
Virtual LANs (VLANs) standard: 802.1Q, IEEE, 1998,
LANE Standard: LAN Emulation Over ATM Version 2—LUNI Specification, af-lane-0084.00, ATM Forum, July 1997, available over the Internet at www.atmforum.com,
MPOA standard: Multi-Protocol Over ATM Specification v1.0, af-mpoa-0087.000, ATM Forum, July 1997, available over the Internet at www.atmforum.com,
“Layer
3
switches”, InfoWorld magazine, Jun. 1, 1998 (Vol. 20, Issue 22), available over the Internet from www.infoworld.com,
the following Internet RFC documents, which are available over the Internet from, for example, the IETF home page at www.ietf.org: IP—RFC 791 (“Internet Protocol”), ARP—RFC 826 (“Address Resolution Protocol”), RFC 1812 (“Requirements for IP version 4 Routers”), RFC 1700 (“ASSIGNED NUMBERS”), RFC 1256 (“ICMP Router Discovery Messages”), SNMP—RFC 1157 (“Simple Network Management Protocol”), RFC 1213 (“Management Information Base for Network Management of TCP/IP-based internets: MIB-II”), VRRP—RFC 2338 (“Virtual Router Redundancy Protocol”) and HSRP RFC 2281 (“Cisco Hot Standby Router Protocol”).
Most routing-switches/switch-routers/layer-
3
-switches known today follow the same network architecture principles as traditional routers, in the sense that each switch is a routing entity, running routing protocols and requiring the configuration and maintenance of a router. If such layer
3
switches are installed centrally only in some locations in the network, while the rest of the network switches are layer
2
only, then the performance of layer
3
forwarding is limited. In order to achieve a distributed layer
3
switching system, such that the function of layer
3
forwarding is done in the most appropriate point in the network, this design calls for many or all of the network switches to be layer
3
switches. This requires the configuration and maintenance of multiple routing entities in the local area network, which is a significant configuration burden.
Some switching systems are designed around the concept of a central routing server with distributed layer-
3
forwarding engines. These systems require a special protocol to communicate forwarding information between the routing server and the layer
3
forwarding engines. Some of these systems implement the MPOA standard for ATM networks. In Ethernet networks these protocols are proprietary requiring that the routing server and all layer
3
forwarding devices be from a single vendor, limiting the user's choice. Also, the introduction of such systems into an existing network requires a major change to the network.
Some ideas for layer
3
switching based on automatic learning of IP stations have been published. These are used by switches that front end a router to enhance its forwarding performance, and are not described as extended to network-wide distributed layer
3
switching systems. Such switches can perform layer
3
(IP) switching without being a router, i.e. without being known to stations as routers and without requiring the configuration that routers do. They assume the existence of a router in the network, use it as default forwarder and automatically learn information about IP stations.
The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference.
SUMMARY OF THE INVENTION
A preferred embodiment of the present invention seeks to provide a network in which the function of layer
3
forwarding is distributed among multiple switches in the network without any of the multiple switches necessarily being a router. The system shown and described herein does not necessarily follow the ‘routing per port’ approach common with modern layer
3
switches. The layer
3
forwarding is not always performed by the switch that: is closest to the source, rather it may be performed by a switch that is on the path from the router to the destination, in addition to being on the path from the source to the router.
Another preferred embodiment of the present invention seeks to allow a switch (or switches) to boost an entire network, rather than boosting a specific router. This embodiment is useful, for example, in providing distributed layer
3
forwarding in switched Ethernet networks. Another application is in networks including Ethernet and ATM-LANE wherein the present invention is useful in providing high performance layer
3
switching, instead of or in addition to MPOA (multi-protocol over ATM).
In the network-boosting embodiment, the switch does not necessarily know the MAC addresses) of the router(s). Rather, the switch preferably performs the layer
3
forwarding function by itself to packets that require layer
3
forwarding, whether these packets are addressed at the MAC layer to a single router or to different routers. The switch preferably identifies the packets as requiring layer
3
forwarding by means other than recognition of the packet's destination MAC address as being that of the router. Typically, the switch may identify packets requiring layer
3
forwarding by discerning that the destination MAC address of the received packet is different than the MAC address known to the switch as corresponding to the destination IP address of the packet.
There is thus provided, in accordance with a preferred embodiment of the present invention, a method by which a network element, having a plurality of ports, performs layer
3
forwarding within a network including at least one router, the method including identifying, for each router in the network, at least one of the plurality of ports, via which the router is reachable, as an upstream port with respect to the router, and identifying at least one other ports as downstream ports with respect to the router, and, upon receiving a packet whose layer
2
destination is the router, performing layer
3
forwarding if the network element is in possession of forwarding information indicating that the packet's layer
3
destination is reachable via any of the downstream ports with regard to the router.
Further in accordance with a preferred embodiment of the present invention, a packet on which layer
3
forwarding is not performed by the network element is forwarded by the network element at layer
2
.
Further in accordance with a preferred embodiment of the present invention, the packet has a layer
3
source and a layer
3
destination which are in different subnets.
Still further in accordance with a preferred embodiment of the present invention, the method also includes learning the forwarding information.
Additionally in accordance with a preferred embodiment of the present invention, the forwarding information includes the VLAN ID corresponding to the layer
3
destination of the packet.
Still further in accordance with a preferred embodiment of the present invention, the forwarding information includes the layer
2
address corresponding to the layer
3
destination of the packet.
Additionally in accordance with a preferred embodiment of the present invention, the forwarding information is learned at least partly by analyzing packets passing though the network element.
Further in accordance with a preferred embodiment of the present invention, the forwarding information is learned entirely by analyzing packets passing though the network element.
Still further in accordance with a preferred embodiment of the present invention, the forwarding information is learned at least partly by analyzing ARP-packets passing through the network element.
Further in accordance with a preferred embodiment of the present invention, the forwarding information is learned at least partly by analyzing IP-packets passin
Rodrig Benny
Shabtai Lior
Avaya Technology Corp.
Bean Thomas J.
Freedman Barry H.
Hsu Alpus H.
Qureshi Afsar M.
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