Support of unidirectional link in IS-IS without IP encapsulation and in presence of unidirectional return path

• US 7,957,380 B2
• Filed: 11/21/2005
• Issued: 06/07/2011
• Est. Priority Date: 11/21/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Ginsberg, Lester C., Roy, Abhay Kumar, Mirtorabi, Sina
• Primary Examiner(s): Ryman; Daniel J.
• Assistant Examiner(s): OH, ANDREW CHUNG SUK
• Application Number:
  US11/284,639
• Publication Number:
  US 20070115989A1
• Time in Patent Office: 2,024 Days
• Field of Search: None
• US Class Current: 370/392
• CPC Class Codes: H04L 45/02 Topology update or discovery
• CPC Class Codes: H04L 45/32 Flooding denial of service attacks H04L63/1458

Abstract

The present invention supports the operation of IS-IS over UDLs without the need for encapsulation of IS-IS PDUs in IP and without the need for a large-scale upgrade of the protocol in the network. The present invention also supports adjacency establishment when the return path from a router at the receive end of a to the router at the transmit end of the unidirectional link is via another unidirectional link.

Claims

1. A method for communicating between a first router and a second router over a unidirectional communication link, the method comprising:

initiating, by the first router, establishment of an adjacency between the first router and the second router by sending one or more point-to-point intermediate system-to-intermediate system (IS-IS) hello (IIH) messages over the unidirectional communication link, the unidirectional communication link connecting the first router to the second router, the one or more IIH messages containing three-way handshake information to transition the adjacency between the first router and the second router to an INIT state;

applying a flooding rule to one or more additional unidirectional communication links on a return path between the second router and the first router to cause the one or more additional unidirectional communication links to pass link state packets (LSPs even when an adjacency on the one or more additional unidirectional communication links is not UP;

receiving, by the first router, one or more LSPs containing three-way handshake information that includes a state of the adjacency between the first router and the second router, and, in response thereto, transitioning the adjacency between the first router and the second router from the INIT state to an UP state; and

sending, by the first router, to the second router, one or more sequence number packets.

2. The method of claim 1, further comprising the first router sending the second router LSPs stored on the first router.

3. The method of claim 2, further comprising the first router receiving from the second router partial sequence number packets.

4. The method of claim 1, wherein, in one or more IIH messages that the first router sends over the unidirectional communication link to the second router, the first router includes circuit information related to the second router.

5. The method of claim 1, wherein the first router sends at least one LSP to the second router in an action triggered by the first router receiving an LSP.

6. The method of claim 1, further comprising the first router validating the one or more received LSPs containing three-way handshake information.

7. The method of claim 1, wherein the one or more LSPs containing three-way handshake information store the three-way handshake information in a unidirectional communication link (UDL) type length value (TLV) structure of the LSPs.

8. The method of claim 1, wherein the one or more LSPs containing three-way handshake information are LSP fragments.

9. The method of claim 1, wherein the return path is a multi-hop return path between the second router and the first router that does not traverse the unidirectional communication link and the one or more LSPs containing three-way handshake information are received on the multi-hop return path between the second router and the first router that does not traverse the unidirectional communication link.

10. The method of claim 9, wherein the multi-hop return path includes the one or more additional unidirectional communication links.

11. The method of claim 1, further comprising:

detecting a loss of connectivity on the return path between the second router and the first router by performing a return path calculation from the second router to the first router.

12. The method of claim 11, wherein the return path calculation is a reverse shortest path first (SPF) calculation from the second router to the first router.

13. A method comprising:

initiating establishment of an adjacency between a first node and a second node by sending one or more hello packets over a unidirectional communication link (UDL), the UDL coupling the first node to the second node, the one or more hello packets containing three-way handshake information;

applying a flooding rule to one or more additional unidirectional communication links on a return path between the second node and the first node to cause the one or more additional unidirectional communication links to pass link state packets (LSPs) even when an adjacency on the one or more additional unidirectional communication links is not UP;

receiving, at the first node, one or more LSPs from the second node that include a type length value (TLV) structure containing three-way handshake information at the first node, and in response thereto, transitioning the adjacency between the first node and the second node to an UP state; and

sending, from the first node to the second node, one or more sequence number packets (SNPs) that include information descriptive of a link state database of the first node.

14. The method of claim 13, wherein the return path is a multi-hop return path between the second node and the first node that does not traverse the unidirectional communication link, and wherein an LSP that includes the TLV structure containing three-way handshake information is received on the multi-hop return path.

15. The method of claim 14, wherein the multi-hop return path includes the one or more additional unidirectional communication links.

16. The method of claim 13, further comprising:

detecting a loss of connectivity on the return path between the second node and the first node by performing a return path calculation from the second node to the first node.

17. The method of claim 16, wherein the return path calculation is a reverse shortest path first (SPF) calculation from the second node to the first node.

18. The method of claim 13, wherein the one or more LSPs containing three-way handshake information are intermediate system-to-intermediate system (IS-IS) LSP fragments.

19. The method of claim 13 wherein the one or more hello packets are intermediate system-to-intermediate system (IS-IS) hello (IIH) messages.

20. A router, comprising:

a communications connection; and

a processor configured to

initiate establishment of an adjacency between the router and a second router by sending one or more hello packets over a unidirectional communication link (UDL) to the second router, the one or more hello packets containing three-way handshake information,

cause a flooding rule to be applied to one or more additional unidirectional communication links on a return path from the second router to the communication connection of the router, to cause the one or more additional unidirectional communication links to pass link state packets (LSPs) even when an adjacency on the one or more additional unidirectional communication links is not UP,

receive one or more LSPs from the second router that include a type length value (TLV) structure containing three-way handshake information, and in response thereto, transitioning the adjacency between the router and the second router to an UP state, and

send the second router one or more sequence number packets (SNPs) that include information descriptive of a link state database.

21. The router of claim 20, wherein the return path is a multi-hop return path between the second router and the router that does not traverse the unidirectional communication link, and wherein an LSP that includes the TLV structure containing three-way handshake information is received on the multi-hop return path.

22. The router of claim 20, wherein the one or more LSPs that include the TLV structure containing three-way handshake information are intermediate system-to-intermediate system (IS-IS) LSP fragments.

23. The router of claim 20, wherein the one or more hello packets are intermediate system-to-intermediate system (IS-IS) hello (IIH) messages.