Remote survivable DHCP for a DHCP relay agent

• US 20060218252A1
• Filed: 03/22/2005
• Published: 09/28/2006
• Est. Priority Date: 03/22/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Ford, Alan
• Granted Patent: US 7,711,826 B2
• Time in Patent Office: Days
• US Class Current: 709/220
• CPC Class Codes: H04L 61/5014 using dynamic host configuration protocol [DHCP] or bootstrap protocol [BOOTP]
• CPC Class Codes: H04L 61/5053 Lease time; Renewal aspects
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06

Abstract

A remote survivable DHCP technique is described for facilitating communications between nodes of a computer network. According to a specific embodiment, the network include a remote survivable DHCP (RSD) system adapted to enable a DHCP relay agent to temporarily respond, during at least a portion of times when the DHCP server is down or unreachable, to DHCP-related requests from clients that have already received a valid DHCP lease offer from a DHCP server during at least a portion of times when the DHCP server is down or unreachable.

Claims

1. A method for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the method comprising:

detecting a first DHCP-related request message sent from the first client system to the first DHCP server system;

determining that the first DHCP server system is unavailable;

retrieving information relating to a first DHCP lease associated with the first client system, the first DHCP lease including DHCP lease information specifying a first assigned network address and a first lease time value;

calculating, using at least a portion of the retrieved DHCP lease information, an updated lease time value to be associated with the first DHCP lease; and

generating a first DHCP response message in response to the first DHCP-related request message, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value.

2. The method of claim 1 wherein the first DHCP response message is generated by the first DHCP relay agent, the method further comprising transmitting the first DHCP response message from the first DHCP relay agent to the first client system.

3. The method of claim 1 wherein the first DHCP response message corresponds to a spoofed DHCPOFFER generated by the first DHCP relay agent spoofing the first DHCP server system, the spoofed DHCPOFFER message including an updated DHCP lease offer specifying the first assigned network address and the updated lease time value.

4. The method of claim 1 further comprising:

detecting a DHCPOFFER message sent from the first DHCP server system to the first client system, the DHCPOFFER message including DHCP lease information specifying an assigned network address, and a lease time value.

5. The method of claim 1 wherein the first DHCP response message is not generated by a DHCP server system.

6. The method of claim 1:

wherein the first DHCP lease information includes information relating to a first timestamp value corresponding to a time when the first DHCP lease was established; and

wherein the updated lease time value is calculated according to;

updated lease time value=first lease time value−

(current timestamp value−

first timestamp value).

7. The method of claim 1 wherein the updated lease time value is calculated according to:

updated lease time value=first lease time value−

time elapsed since initialization of the first DHCP lease.

8. The method of claim 1 further comprising:

monitoring information contained in messages that are exchanged between the first client system and the first DHCP server system; and

recording at least a portion of DHCP-related information obtained from the monitored messages.

9. The method of claim 1 wherein the first DHCP-related request message corresponds to a DHCPDISCOVER message, the method further comprising determining whether the first client system has associated therewith an unexpired DHCP lease.

10. The method of claim 1 further comprising generating the first DHCP response message only in response to a determination that the updated lease time value exceeds a predetermined threshold value T.

11. The method of claim 1:

wherein the computer network corresponds to a cable network;

wherein the first client system corresponds to a cable modem; and

wherein the first DHCP relay agent corresponds to a Cable Modem Termination System (CMTS).

12. The method of claim 1 wherein the computer network further comprising a first remote survivable DHCP system adapted to enable the first DHCP relay agent to temporarily respond, during at least a portion of times when the DHCP server is down or unreachable, to DHCP-related requests from clients that have already received a valid DHCP lease offer from the first DHCP server.

13. A method for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the method comprising:

allocating a first DHCP lease to the first client system, the first DHCP lease including first DHCP lease information relating to a first network address and a first lease time value;

detecting a DHCPDISCOVER message from the first client system;

determining that the first DHCP server system is unavailable;

calculating an updated lease time value to be associated with the first DHCP lease; and

generating, at the DHCP relay agent, a DHCPOFFER message in response to the DHCPDISCOVER message, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value.

14. The method of claim 13 wherein the DHCPOFFER message includes DHCP lease parameters substantially identical to DHCP lease parameters specified in the first DHCP lease, with the exception that a value of the lease time parameter is equal to the updated lease time value.

15. The method of claim 13 further comprising generating the first DHCP response message only in response to a determination that the updated lease time value exceeds a predetermined threshold value T.

16. The method of claim 13:

wherein the first DHCP lease information includes information relating to a first timestamp value corresponding to a time when the first DHCP lease was established; and

wherein the updated lease time value is calculated according to;

updated lease time value=first lease time value−

(current timestamp value−

first timestamp value).

17. The method of claim 13 wherein the updated lease time value is calculated according to:

updated lease time value=first lease time value−

time elapsed since initialization of the first DHCP lease.

18. The method of claim 13 wherein the first DHCP response message corresponds to a spoofed DHCPOFFER generated by the first DHCP relay agent spoofing the first DHCP server system, the spoofed DHCPOFFER message including an updated DHCP lease offer specifying the first assigned network address and the updated lease time value.

19. The method of claim 13 wherein the computer network further comprising a first remote survivable DHCP system adapted to enable the first DHCP relay agent to temporarily respond, during at least a portion of times when the DHCP server is down or unreachable, to DHCP-related requests from clients that have already received a valid DHCP lease offer from the first DHCP server.

20. A system for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the system comprising:

at least one processor;

at least one interface configured or designed to provide a communication link to at least one other network device in the data network; and

memory;

the system being configured or designed to detect a first DHCP-related request message sent from the first client system to the first DHCP server system;

the system being configured or designed to determine that the first DHCP server system is unavailable;

the system being configured or designed to retrieve information relating to a first DHCP lease associated with the first client system, the first DHCP lease including DHCP lease information specifying a first assigned network address and a first lease time value;

the system being configured or designed to calculate, using at least a portion of the retrieved DHCP lease information, an updated lease time value to be associated with the first DHCP lease; and

the system being configured or designed to generate a first DHCP response message in response to the first DHCP-related request message, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value.

21. The system of claim 20 wherein the first DHCP response message is generated by the first DHCP relay agent, the system being further configured or designed to transmit the first DHCP response message from the first DHCP relay agent to the first client system.

22. The system of claim 20 wherein the first DHCP response message corresponds to a spoofed DHCPOFFER generated by the first DHCP relay agent spoofing the first DHCP server system, the spoofed DHCPOFFER message including an updated DHCP lease offer specifying the first assigned network address and the updated lease time value.

23. The system of claim 20 being further configured or designed to:

detect a DHCPOFFER message sent from the first DHCP server system to the first client system, the DHCPOFFER message including DHCP lease information specifying an assigned network address, and a lease time value.

24. The system of claim 20 wherein the first DHCP response message is not generated by a DHCP server system.

25. The system of claim 20:

wherein the first DHCP lease information includes information relating to a first timestamp value corresponding to a time when the first DHCP lease was established; and

wherein the updated lease time value is calculated according to;

updated lease time value=first lease time value−

(current timestamp value−

first timestamp value).

26. The system of claim 20 wherein the updated lease time value is calculated according to:

updated lease time value=first lease time value−

time elapsed since initialization of the first DHCP lease.

27. The system of claim 20 being further configured or designed to:

monitor information contained in messages that are exchanged between the first client system and the first DHCP server system; and

record at least a portion of DHCP-related information obtained from the monitored messages.

28. The system of claim 20 wherein the first DHCP-related request message corresponds to a DHCPDISCOVER message, the system being further configured or designed to determine whether the first client system has associated therewith an unexpired DHCP lease.

29. The system of claim 20 being further configured or designed to generate the first DHCP response message only in response to a determination that the updated lease time value exceeds a predetermined threshold value T.

30. The system of claim 20:

wherein the computer network corresponds to a cable network;

wherein the first client system corresponds to a cable modem; and

wherein the first DHCP relay agent corresponds to a Cable Modem Termination System (CMTS).

31. The system of claim 20 wherein the system corresponds to a remote survivable DHCP system adapted to enable the first DHCP relay agent to temporarily respond, during at least a portion of times when the DHCP server is down or unreachable, to DHCP-related requests from clients that have already received a valid DHCP lease offer from the first DHCP server.

32. A system for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the system comprising:

at least one processor;

at least one interface configured or designed to provide a communication link to at least one other network device in the data network; and

memory;

the system being configured or designed to allocate a first DHCP lease to the first client system, the first DHCP lease including first DHCP lease information relating to a first network address and a first lease time value;

the system being configured or designed to detect a DHCPDISCOVER message from the first client system;

the system being configured or designed to determine that the first DHCP server system is unavailable;

the system being configured or designed to calculate an updated lease time value to be associated with the first DHCP lease; and

the system being configured or designed to generate, at the DHCP relay agent, a DHCPOFFER message in response to the DHCPDISCOVER message, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value.

33. The system of claim 32 wherein the DHCPOFFER message includes DHCP lease parameters substantially identical to DHCP lease parameters specified in the first DHCP lease, with an exception that a value of the lease time parameter is equal to the updated lease time value.

34. The system of claim 32 being further configured or designed to generate the first DHCP response message only in response to a determination that the updated lease time value exceeds a predetermined threshold value T.

35. The system of claim 32:

wherein the first DHCP lease information includes information relating to a first timestamp value corresponding to a time when the first DHCP lease was established; and

wherein the updated lease time value is calculated according to;

updated lease time value=first lease time value−

(current timestamp value−

first timestamp value).

36. The system of claim 32 wherein the updated lease time value is calculated according to:

updated lease time value=first lease time value−

time elapsed since initialization of the first DHCP lease.

37. The system of claim 32 wherein the first DHCP response message corresponds to a spoofed DHCPOFFER generated by the first DHCP relay agent spoofing the first DHCP server system, the spoofed DHCPOFFER message including an updated DHCP lease offer specifying the first assigned network address and the updated lease time value.

38. The system of claim 32 wherein the system corresponds to a remote survivable DHCP system adapted to enable the first DHCP relay agent to temporarily respond, during at least a portion of times when the DHCP server is down or unreachable, to DHCP-related requests from clients that have already received a valid DHCP lease offer from the first DHCP server.

39. A system for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the method comprising:

means for detecting a first DHCP-related request message sent from the first client system to the first DHCP server system;

means for determining that the first DHCP server system is unavailable;

means for retrieving information relating to a first DHCP lease associated with the first client system, the first DHCP lease including DHCP lease information specifying a first assigned network address and a first lease time value;

means for calculating, using at least a portion of the retrieved DHCP lease information, an updated lease time value to be associated with the first DHCP lease; and

means for generating a first DHCP response message in response to the first DHCP-related request message, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value.

40. A system for facilitating communication between nodes of at least one computer network, the computer network including a first client system, a first DHCP server system, and a first DHCP relay agent, the DHCP relay agent being configured or designed to facilitate communications between the first client system and the first DHCP server system, the method comprising:

means for allocating a first DHCP lease to the first client system, the first DHCP lease including first DHCP lease information relating to a first network address and a first lease time value;

means for detecting a DHCPDISCOVER message from the first client system;

means for determining that the first DHCP server system is unavailable;

means for calculating an updated lease time value to be associated with the first DHCP lease; and

means for generating, at the DHCP relay agent, a DHCPOFFER message in response to the DHCPDISCOVER message, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value.