Remote survivable DHCP for a DHCP relay agent

• US 7,711,826 B2
• Filed: 03/22/2005
• Issued: 05/04/2010
• 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
• Primary Examiner(s): Nguyen; Dustin
• Application Number:
  US11/087,194
• Publication Number:
  US 20060218252A1
• Time in Patent Office: 1,869 Days
• Field of Search: 370/331, 370/338, 370/395.5, 370/401, 370/466, 455/435.1, 709/250, 709/220, 709/222, 709/224, 709/230, 709/225, 398/1
• US Class Current: 709/227
• 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 first 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;

in response to 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

comparing the updated lease time value against a predetermined threshold value T; and

generating and sending a first DHCP response message in response to the first DHCP-related request message based upon a result of comparing the updated lease time value against the predetermined threshold value T, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value, wherein sending the first DHCP response message is performed without waiting until the first DHCP server system is available.

48. The method as recited in 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).

49. The method as recited in 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.

50. The method as recited in claim 1, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable.

2. 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 first DHCP relay agent being operable 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; and

initiating a first set of operations in response to detecting that the first DHCP server system is unavailable, wherein the first set of operations includes;

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;

comparing the updated lease time value against a predetermined threshold value T; and

generating and sending a first DHCP response message in response to the first DHCP-related request message according to a result of comparing the updated lease time value against the predetermined threshold value T, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value, wherein sending the first DHCP response message is performed without waiting until the first DHCP server system is available.

3. The method of claim 2 further comprising:

periodically pinging the first DHCP server system in order to detect whether the first DHCP server system is unavailable.

4. The method of claim 2 further comprising:

periodically generating and sending DHCPDISCOVER messages to the first DHCP server system in order to detect whether the first DHCP server system is unavailable.

5. The method of claim 2 further comprising:

monitoring a success rate of DHCP requests forwarded to the first DHCP server in order to detect whether the first DHCP server system is unavailable.

6. The method of claim 2 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.

7. The method of claim 2 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.

8. The method of claim 2 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.

9. The method of claim 2 wherein the first DHCP response message is not generated by a DHCP server system.

10. The method of claim 2:

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).

11. The method of claim 2:

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.

12. The method of claim 2 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.

13. The method of claim 2 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.

14. The method of claim 2 further comprising generating and sending the first DHCP response message only in response to a determination that the updated lease time value exceeds the predetermined threshold value T.

15. The method of claim 2:

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).

16. The method of claim 2 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 first 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.

51. The method as recited in claim 2, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable.

17. 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 first DHCP relay agent being operable 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;

initiating a first set of operations in response to detecting that the first DHCP server system is unavailable, wherein the first set of operations includes;

calculating an updated lease time value to be associated with the first DHCP lease, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable;

comparing the updated lease time value against a predetermined threshold value T; and

generating and sending, at the DHCP relay agent, a DHCPOFFER message in response to the DHCPDISCOVER message based upon a result of comparing the updated lease time value against the predetermined threshold value T, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value, wherein sending the DHCPOFFER message is performed without waiting until the first DHCP server system is available.

18. The method of claim 17 wherein the DHCPOFFER message includes DHCP lease parameters 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.

19. The method of claim 17 further comprising generating and sending the first DHCP response message only in response to a determination that the updated lease time value exceeds the predetermined threshold value T.

20. The method of claim 17

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).

21. The method of claim 17 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.

22. The method of claim 17 wherein the first DHCP response message corresponds to a spoofed DHCPOFFER generated by the first DHCP relay agent spooling 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 method of claim 17 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 first 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.

24. 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 first DHCP relay agent being operable 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 operable to provide a communication link to at least one other network device in the data network; and

memory;

the system being operable to;

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

retrieve, in response to detecting that the first DHCP server system is unavailable, 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;

calculate, using at least a portion of the retrieved DHCP lease information and in response to detecting that the first DHCP server system is unavailable, an updated lease time value to be associated with the first DHCP lease, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable;

compare the updated lease time value against a predetermined threshold value T; and

generate and send, in response to detecting that the first DHCP server system is unavailable, a first DHCP response message in response to the first DHCP-related request message according to a result of comparing the updated lease time value against the predetermined threshold value T, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value, wherein the first DHCP response message is sent without waiting until the first DHCP server system is available.

25. The system of claim 24 being further operable to:

periodically ping the first DHCP server system in order to detect whether the first DHCP server system is unavailable.

26. The system of claim 24 being further operable to:

periodically generate and send DHCPDISCOVER messages to the first DHCP server system in order to detect whether the first DHCP server system is unavailable.

27. The system of claim 24 being further operable to:

monitor a success rate of DHCP requests forwarded to the first DHCP server in order to detect whether the first DHCP server system is unavailable.

28. The system of claim 24 wherein the first DHCP response message is generated by the first DHCP relay agent, the system being further operable to transmit the first DHCP response message from the first DHCP relay agent to the first client system.

29. The system of claim 24 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.

30. The system of claim 24 being further operable 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.

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

32. The system of claim 24

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).

33. The system of claim 24 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.

34. The system of claim 24 being further operable 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.

35. The system of claim 24 wherein the first DHCP-related request message corresponds to a DHCPDISCOVER message, the system being further operable to determine whether the first client system has associated therewith an unexpired DHCP lease.

36. The system of claim 24 being further operable to generate and send the first DHCP response message only in response to a determination that the updated lease time value exceeds the predetermined threshold value T.

37. The system of claim 24:

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).

38. The system of claim 24 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 first 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 first DHCP relay agent being operable 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 operable to provide a communication link to at least one other network device in the data network; and

memory;

the system being operable 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 operable to detect a DHCPDISCOVER message from the first client system;

the system being operable to determine that the first DHCP server system is unavailable;

the system being operable to calculate, in response to detecting that the first DHCP server system is unavailable, an updated lease time value to be associated with the first DHCP lease, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable;

the system being operable to compare the updated lease time value against a predetermined threshold value T; and

the system being operable to generate and send, at the first DHCP relay agent and in response to detecting that the first DHCP server system is unavailable, a DHCPOFFER message in response to the DHCPDISCOVER message according to a result of comparing the updated lease time value against a predetermined threshold value T, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value.

40. The system of claim 39 wherein the DHCPOFFER message includes DHCP lease parameters 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.

41. The system of claim 39 being further operable to generate and send the first DHCP response message only in response to a determination that the updated lease time value exceeds the predetermined threshold value T.

42. The system of claim 39:

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).

43. The system of claim 39 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.

44. The system of claim 39 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.

45. The system of claim 39 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 first 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.

46. 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 first DHCP relay agent being operable to facilitate communications between the first client system and the first DHCP server system, the method comprising:

at least one processor;

memory;

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, in response to detecting that the first DHCP server system is unavailable, 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 and in response to detecting that the first DHCP server system is unavailable, an updated lease time value to be associated with the first DHCP lease, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable;

means for comparing the updated lease time value against a predetermined threshold value T; and

means for generating, in response to detecting that the first DHCP server system is unavailable, a first DHCP response message in response to the first DHCP-related request message according to a result of comp arm g the updated lease time value against the predetermined threshold value T, wherein the first DHCP response message includes updated DHCP lease information specifying the first assigned network address and the updated lease time value.

47. 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 first DHCP relay agent being operable to facilitate communications between the first client system and the first DHCP server system, the method comprising:

at least one processor;

memory;

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, in response to detecting that the first DHCP server system is unavailable, an updated lease time value to be associated with the first DHCP lease, wherein the updated lease time value is unrelated to a time during which the first DHCP server system is unavailable;

means for comparing the updated lease time value against a predetermined threshold value T; and

means for generating and sending, at the DHCP relay agent and in response to detecting that the first DHCP server system is unavailable, a DHCPOFFER message in response to the DHCPDISCOVER message based upon comparing the updated lease time value against the predetermined threshold value T, wherein DHCPOFFER message includes parameters specifying the first network address and the updated lease time value, wherein sending the DHCPOFFER message is performed without waiting until the first DHCP server system is available.