Apparatus and methods for routerless layer 3 forwarding in a network

• US 6,256,314 B1
• Filed: 08/11/1998
• Issued: 07/03/2001
• Est. Priority Date: 08/11/1998
• Status: Expired due to Term

• Current Assignee: Avaya Incorporated
• Original Assignee: Avaya Technology Corporation Miami Lakes FLA US
• Inventors: Shabtai, Lior, Rodrig, Benny
• Primary Examiner(s): Hsu, Alpus H.
• Assistant Examiner(s): Qureshi, Afsar M.
• Application Number:
  US09/132,030
• Time in Patent Office: 1,057 Days
• Field of Search: 370/254, 370/255, 370/352, 370/389, 370/392, 370/400, 370/401, 370/409, 370/428, 370/469, 370/424, 709/220, 709/230, 709/238
• US Class Current: 370/401
• CPC Class Codes: H04L 49/354 for supporting virtual local area networks [VLAN]
• CPC Class Codes: H04L 49/602 Multilayer or multiprotocol switching, e.g. IP switching

Abstract

A layer 3 forwarding method for layer 3 forwarding an individual packet from a station I to a station II wherein the packet'"'"'s layer 2 destination includes a router within the network which is reachable from a network element A via which stations I and II are connected to the network, the router storing ARP information, the method including providing network element A with a capability to perform layer 3 forwarding of a packet from station I to station II, wherein the providing step includes learning, on the part of network element A, of forwarding information used by the router to forward packets from station I to station II, by reading the ARP information of the router and performing layer 3 forwarding on the individual packet, at network element A.

Claims

1. A method by which a network element, having a plurality of ports, performs layer 3 forwarding within a network comprising one or more routers, the method comprising:

for each of the one or more routers in the network, identifying 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 one or more other ports in the plurality of ports from which the router is not reachable as downstream ports with respect to the router;

learning forwarding information including one or more IP addresses respectively associated with one or more IP stations reachable from the one or more other ports;

receiving a data packet; and

performing layer 3 forwarding upon receiving the packet if the packet has a layer 2 destination address equal to a MAC address for one of the one or more routers and has a layer 3 IP destination address equal to one of the one or more learned IP addresses.

2. A method according to claim 1 wherein the packet has a layer 3 IP source address and a layer 3 IP destination address which are in different subnets.

3. A method according to claim 1 wherein the forwarding information comprises the VLAN ID corresponding to the layer 3 IP destination address of the packet.

4. A method according to claim 1 wherein the forwarding information comprises the layer 2 MAC address corresponding to the layer 3 IP destination address of the packet.

5. A method according to claim 1 wherein the forwarding information is learned at least partly by analyzing IP packets passing though the network element.

6. A method according to claim 5 wherein the forwarding information is learned at least partly by analyzing ARP-packets passing through the network element.

7. A method according to claim 6 wherein the forwarding information is learned at least partly by analyzing layer 3 IP packets passing through the network element whose source layer 2 MAC address is an address of a router.

8. A method according to claim 1 wherein the forwarding information is learned entirely by analyzing IP packets passing though the network element.

9. A method according to claim 1 wherein said forwarding information comprises information pertaining only to stations whose IP addresses have been designated by the user as being eligible to be learned.

10. A method according to claim 1 wherein a packet on which layer 3 forwarding is not performed by the network element is forwarded by the network element at layer 2.

11. A layer 3 forwarding method for layer 3 forwarding an individual packet from a station I to a station II wherein the packet'"'"'s layer 2 destination comprises a router within the network which is reachable from a network element A via which stations I and II are connected to the network, the router storing ARP information, the method comprising:

providing network element A with a capability to perform layer 3 forwarding of a packet from station I to station II, wherein said providing step comprises learning, on the part of network element A, of forwarding information used by the router to forward packets from station I to station II, by reading said ARP information of the router; and

performing layer 3 forwarding on said individual packet, at network element A.

12. A method according to claim 11 wherein said step of reading said ARP information comprises using an SNMP mechanism to read said ARP information.

13. A method by which a network element, having a plurality of ports, performs layer 3 forwarding, using forwarding information, within a network comprising at least one router, the method comprising:

learning forwarding information pertaining to stations whose IP addresses have been designated by the user as being eligible to be learned;

upon receiving a packet, determining whether or not the packet requires layer 3 forwarding, without using any information regarding the identity of the router; and

performing layer 3 forwarding if the packet requires layer 3 forwarding and if all necessary forwarding information is available, and performing layer 2 forwarding otherwise.

14. A method according to claim 13 wherein the layer 3 source of the packet and the layer 3 destination of the packet are in different subnets.

15. A method according to claim 13 wherein the forwarding information comprises the VLAN ID corresponding to the layer 3 destination of the packet.

16. A method according to claim 13 wherein the forwarding information comprises the layer 2 address corresponding to the layer 3 destination of the packet.

17. A method according to claim 16 wherein layer 3 forwarding is performed on said packet by the network element, only if said layer 2 address corresponding to the packet'"'"'s layer 3 destination, as known to the network element, is different than the destination layer 2 address of said packet.

18. A method according to claim 17 wherein a packet on which layer 3 forwarding is not performed by the network element is forwarded by the network element at layer 2.

19. A method according to claim 13 wherein the forwarding information is learned at least partly by analyzing packets passing though the network element.

20. A method according to claim 19 wherein the forwarding information is learned at least partly by analyzing ARP-packets passing through the network element.

21. A method according to claim 19 wherein the forwarding information is learned at least partly by analyzing IP-packets passing through the network element.

22. A method according to claim 19 wherein the forwarding information is learned at least partly by analyzing layer 3 packets passing through the network element whose source layer 2 address is an address of a router.

23. A method according to claim 13 wherein the forwarding information is learned entirely by analyzing packets passing though the network element.

24. A method according to claim 13 wherein layer 3 forwarding of said packet is performed by the network element only if the destination layer 2 address of said packet is known to the network element to be reachable via a port that is different than the port from which said packet was received at the network element.

25. A method according to claim 24 wherein the packet is discarded if the destination layer 2 address of said packet is known to the network element to be reachable via the port from which said packet was received at the network element.

26. A method according to claim 13 wherein said performing step includes changing the source layer 2 address of said packet to a layer 2 address of network element A.

27. A system by which a network element, having a plurality of ports, performs layer 3 forwarding within a network comprising one or more routers, the system comprising:

a port identifier operative, for each router in the network, to identify at least one of the plurality of ports, via which the router is reachable, as an upstream port with respect to the router, and to identify one or more other ports in the plurality of ports from which the router is not reachable as downstream ports with respect to the router;

a learning unit operative to learn forwarding information including one or more IP addresses respectively associated with one or more IP stations reachable from the one or more other ports; and

a layer 3 forwarding unit operative, upon receiving a packet having a layer 2 destination address equal to a MAC address for one of the one or more routers and having a layer 3 IP destination address equal to one of the one or more learned IP addresses, to perform layer 3 forwarding.

28. A layer 3 forwarding system for layer 3 forwarding an individual packet from a station I to a station II wherein the packet'"'"'s layer 2 destination comprises a router within the network which is reachable from a network element A via which stations I and II are connected to the network, the router storing ARP information, the system comprising:

a learning unit operative to provide network element A with a capability to perform layer 3 forwarding of a packet from station I to station II, wherein said providing step comprises learning, on the part of network element A, of forwarding information used by the router to forward packets from station I to station II, by reading said ARP information of the router; and

at network element A, a layer 3 forwarding unit for layer 3 forwarding of said individual packet.

29. A system by which a network element, having a plurality of ports, performs layer 3 forwarding, using forwarding information, within a network comprising at least one router, the system comprising:

means for learning forwarding information pertaining to stations whose IP addresses have been designated by the user as being eligible to be learned;

means for determining, upon receiving a packet, whether or not the packet requires layer 3 forwarding, without using any information regarding the identity of the router; and

means for performing layer 3 forwarding if the packet requires layer 3 forwarding and if all necessary forwarding information is available, and for performing layer 2 forwarding otherwise.