Method and apparatus for implementing forwarding decision shortcuts at a network switch

• US 7,519,062 B1
• Filed: 11/30/2004
• Issued: 04/14/2009
• Est. Priority Date: 10/14/1997
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Edsall, Thomas J., Kloth, Ray, Cafiero, Luca
• Primary Examiner(s): Pham; Chi H.
• Assistant Examiner(s): Hyun; Soon D
• Application Number:
  US10/999,823
• Time in Patent Office: 1,596 Days
• Field of Search: None
• US Class Current: 370/392
• CPC Class Codes: H04L 49/251 Cut-through or wormhole routing
• 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

In one embodiment, a first packet is forwarded based on a network layer routing decision rendered by a router. A shortcut entry is generated based on a first header of the first packet. The shortcut entry is stored. In response to the shortcut entry, and absent a network layer routing decision rendered by a router, subsequent packets having a subsequent header are forwarded if the subsequent header has at least one field which matches a field of the first header. Such technique may be implemented by a switch coupled to the router.

Claims

1. A method, comprising:

forwarding a first packet based on a network layer routing decision rendered by a router for the first packet;

generating a shortcut entry based on a first header of the first packet;

storing the shortcut entry for the first header; and

forwarding, in response to the shortcut entry, and absent a network layer routing decision rendered by a router, subsequent packets having a subsequent header, the subsequent header having at least one field which matches a field of the first header.

2. The method as in claim 1, further comprising:

rendering the network layer routing decision for the first packet in response to a network layer field of the first header.

3. The method as in claim 1, further comprising:

indexing the shortcut entry in response to a network layer field of the first header.

4. The method as in claim 1, further comprising:

forwarding the subsequent packets in response to a network layer field of the subsequent header.

5. The method as in claim 1, further comprising:

rewriting a MAC layer field of the packet before transmitting the packet, an address for rewriting the MAC layer field taken from the shortcut entry.

6. The method as in claim 1, further comprising:

rendering the network layer routing decision for the first packet by software within the router; and

forwarding the subsequent packets in response to the shortcut entry by hardware logic circuits within a switch.

7. The method as in claim 1, further comprising:

storing the shortcut entry in a shortcut table.

8. The method as in claim 1, further comprising:

receiving a second packet having a second header;

reading the second header by a hardware logic circuit;

determining, by the hardware logic circuit, if there is a match between the second header and an entry in the shortcut table, and if there is a match, forwarding the second packet by the hardware logic circuit, and if there is no match, forwarding the packet to a router to render a network layer routing decision and writing an entry in the shortcut table in response to the router'"'"'s network layer routing decisions.

9. A method, comprising:

receiving a first packet having a header, the header including a field indicating a routing decision for the first packet rendered with the assistance of software executing on a router;

forwarding the first packet in response to information read from the header;

storing a shortcut entry for the header of the first packet; and

forwarding a subsequent packet, in response to a header of the subsequent packet and in response to the shortcut entry, by use of hardware logic circuits.

10. An apparatus, comprising:

means for forwarding a first packet based on a network layer routing decision rendered by a router for the first packet;

means for generating a shortcut entry based on a first header of the first packet;

means for storing the shortcut entry for the first header; and

means for forwarding, in response to the shortcut entry, and absent a network layer routing decision rendered by a router, subsequent packets having a subsequent header, the subsequent header having at least one field which matches a field of the first header.

11. The apparatus as in claim 10, further comprising:

means for rendering the network layer routing decision for the first packet in response to a network layer field of the first header.

12. The apparatus as in claim 10, further comprising:

means for indexing the shortcut entry in response to a network layer field of the first header.

13. The apparatus as in claim 10, further comprising:

means for forwarding the subsequent packets in response to a network layer field of the subsequent header.

14. The apparatus as in claim 10, further comprising:

means for rewriting a MAC layer field of the packet before transmitting the packet, an address for rewriting the MAC layer field taken from the shortcut entry.

15. The apparatus as in claim 10, further comprising:

means for rendering the network layer routing decision for the first packet by software within the router; and

means for forwarding the subsequent packets in response to the shortcut entry by hardware logic circuits within a switch.

16. The apparatus as in claim 10, further comprising:

means for storing the shortcut entry in a shortcut table.

17. The apparatus as in claim 10, further comprising:

means for receiving a second packet having a second header;

means for reading the second header;

means for determining, if there is a match between the second header and an entry in the shortcut table, and if there is a match, forwarding the second packet, and if there is no match, forwarding the packet to s router to render a network layer routing decision and writing an entry in the shortcut table in response to the router'"'"'s network layer routing decision.

18. An apparatus, comprising:

means for receiving a first packet having a header, the header including a field indicating a routing decision for the first packet rendered with the assistance of software executing on a router;

means for forwarding the first packet in response to information read from the header;

means for storing a shortcut entry for the header of the first packet; and

means for forwarding a subsequent packet, in response to a header of the subsequent packet and in response to the shortcut entry, by use of hardware logic circuits.

19. A apparatus, comprising:

a first port to receive packets;

a parsing engine to read a first header of a first packet;

a second port for transmitting packets, the first packet transmitted in response to a network layer routing decision rendered by a router, the decision based on the first header;

a shortcut table to store shortcut entries for forwarding packets, an entry written into the shortcut table in response to the first header; and

a shortcut engine to forward a subsequent packet having a sub-sequent header, absent a network layer routing decision by a router, the subsequent header having a match with an entry in the shortcut table.

20. The apparatus as in claim 19, further comprising:

a layer 2 forwarding engine to forward the first packet in response to a field of the first header.

21. The apparatus as in claim 19, further comprising:

the shortcut entry indexed in response to a network layer field of the first header.

22. The apparatus as in claim 19, further comprising:

the shortcut engine to forward the subsequent packets in response to a network layer field of the subsequent header.

23. The apparatus as in claim 19, further comprising:

a rewrite engine to rewrite a MAC address of a packet to be forwarded, to forward the first packet in response to a network layer field of the first header.

24. An apparatus, comprising:

an interface to receive a first packet having a header, the header including a field indicating a routing decision for the first packet rendered with the assistance of software on a router;

a forwarding engine to forward the first packet in response to information read from the header;

a shortcut table to store a shortcut entry for the header of the first packet; and

a shortcut engine to forward subsequent packets, in response to a header of the subsequent packet and in response to the shortcut entry, by use of hardware logic circuits.

25. A computer readable media, comprising:

said computer readable media containing instructions for execution on a processor for the practice of a method, the method having the steps of,

forwarding a first packet based on a network layer routing decision rendered for the first packet;

generating a shortcut entry based on a first header of the first packet;

storing a shortcut entry for the first header; and

forwarding, in response to the shortcut entry, and absent a network layer routing decision, subsequent packets having a subsequent header, the subsequent header having at least one field which matches a field of the first header.

26. A computer readable media, comprising:

said computer readable media containing instructions for execution on a processor for the practice of a method, the method having the steps of,

receiving a first packet having a header, the header including a field indicating a routing decision for the first packet rendered with the assistance of software executing on a router;

forwarding the first packet in response to information read from the header;

storing the shortcut entry for the header of the first packet; and

forwarding subsequent packets, in response to a header of the subsequent packet and in response to the shortcut entry, by use of hardware logic circuits.