Computing path maximum transmission unit size

Patent metadata

Field	Value
Publication number	US-9923835-B1
Application number	US-201514862797-A
Country	US
Kind code	B1
Filing date	Sep 23, 2015
Priority date	Sep 23, 2015
Publication date	Mar 20, 2018
Grant date	Mar 20, 2018

Abstract

Techniques include quickly establishing a maximum transmission unit (MTU) for a network path, such as a network tunnel. In one example, data representative of the MTU is included in a header of a packet. If the MTU indicated in the packet is larger than a downstream network interface of a network device, the network device updates the data of the header to indicate the MTU of the downstream network interface, and an egress network device sends the packet back to an ingress network device. In another example, network devices fragment packets, if necessary, such that the fragments satisfy the MTU of the downstream network interface. The egress network device then determines the MTU for the path based on a largest received fragment, reassembles the fragments into a single packet, and returns the reassembled packet to the ingress network device. The packets may comprise echo packets of generic routing encapsulation (GRE).

First claim

What is claimed is:

1. A method comprising, by an egress network device of a network path:
receiving a first packet including data indicative of a maximum transmission unit (MTU) for the network path;
forming, from the first packet, a second packet to include a path header corresponding to the network path such that the path header includes the data indicative of the MTU for the network path, wherein forming the second packet comprises:
setting a value of at least one bit of a first set of bits of the path header to a value indicating that the second packet includes the data indicative of the MTU; and
setting a second set of bits of the path header to values representative of the data indicative of the MTU; and

sending the second packet to an ingress network device of the network path.

2. The method of claim 1 , wherein the first packet further includes data indicating that the first packet includes the data indicative of the MTU for the network path.

3. The method of claim 1 , wherein the path header substantially conforms to a generic routing encapsulation (GRE) header, wherein the first set of bits comprises a set of bits that a GRE standard identifies as a reserved 0 field, and wherein the second set of bits comprises a set of bits that the GRE standard identifies as a reserved 1 field.

4. The method of claim 1 , wherein the data indicative of the MTU comprises data indicative of a size of the first packet.

5. The method of claim 1 , wherein the first packet comprises a first fragment of a plurality fragments for a common packet received via the network path, the method further comprising:
determining sizes for the plurality of fragments; and
determining that the size of the first fragment is larger than the sizes for the other fragments of the plurality of fragments,
wherein the data indicative of the MTU comprises data indicative of the size of the first fragment.

6. The method of claim 5 , further comprising receiving the plurality of fragments in accordance with Internet protocol version 4 (IPv4), wherein all but an ordinal last fragment of the plurality of fragments include values of true for more-fragments flags in headers of the plurality of fragments.

7. The method of claim 5 , wherein the first fragment is encapsulated by an inner header and an outer header, and wherein forming the second packet comprises:
reassembling the plurality of fragments into the second packet; and
encapsulating the second packet with the inner header of the first fragment such that the inner header includes the data indicative of the MTU.

8. The method of claim 7 , wherein forming the second packet further comprises removing the outer header from the first fragment.

9. The method of claim 1 , wherein the first packet is encapsulated by an inner header and an outer header, wherein the data indicative of the MTU comprises data of the outer header, and wherein forming the second packet comprises updating a value of the inner header to represent the MTU based on the data of the outer header.

10. The method of claim 9 , wherein forming the second packet further comprises removing the outer header from the first packet.

11. The method of claim 1 , further comprising, prior to receiving the first packet, negotiating, with the ingress network device, a technique by which to send the data indicative of the MTU to the ingress network device.

12. The method of claim 1 , wherein the network path comprises a network tunnel.

13. The method of claim 12 , wherein the network tunnel comprises a generic routing encapsulation (GRE) tunnel.

14. The method of claim 12 , wherein the first packet comprises one of an echo packet of GRE Keepalive, Bidirectional Forwarding Detection (BFD), or Operations, Administration, and Maintenance (OAM).

15. The method of claim 1 , wherein the path header substantially conforms to a generic routing encapsulation (GRE) header, wherein the at least one bit of the first set of bits follows a sequence number bit of the GRE header, and wherein the second set of bits follow a checksum field of the GRE header.

16. An egress network device for a network path, the egress network device comprising:
one or more network interfaces configured to send packets to an upstream network device of the network path and to receive packets from the upstream network device; and
a processing unit implemented in circuitry and configured to:
receive, via the one or more network interfaces, a first packet including data indicative of a maximum transmission unit (MTU) for the network path;
form, from the first packet, a second packet to include a path header corresponding to the network path such that the path header includes the data indicative of the MTU for the network path, wherein to form the second packet, the processing unit is configured to:
set a value of at least one bit of a first set of bits of the path header to a value indicating that the second packet includes the data indicative of the MTU; and
set a second set of bits of the path header to values representative of the data indicative of the MTU; and

send, via the one or more network interfaces and the upstream network device, the second packet to an ingress network device of the network path.

17. The egress network device of claim 16 , wherein the first packet further includes data indicating that the first packet includes the data indicative of the MTU for the network path.

18. The egress network device of claim 16 , wherein the path header substantially conforms to a generic routing encapsulation (GRE) header, wherein the first set of bits comprises a set of bits that a GRE standard identifies as a reserved 0 field, and wherein the second set of bits comprises a set of bits that the GRE standard identifies as a reserved 1 field.

19. The egress network device of claim 16 , wherein the first packet comprises a first fragment of a plurality fragments for a common packet received via the network path,
wherein the processing unit is further configured to:
determine sizes for the plurality of fragments; and
determine that the size of the first fragment is larger than the sizes for the other fragments of the plurality of fragments, and

wherein the data indicative of the MTU comprises data indicative of the size of the first fragment.

20. The egress network device of claim 16 , wherein the first packet is encapsulated by an inner header and an outer header, wherein the data indicative of the MTU comprises data of the outer header, and wherein to form the second packet, the processing unit is configured to:
reassemble the plurality of fragments into the second packet; and
encapsulate the second packet with the inner header of the first fragment such that the inner header includes the data indicative of the MTU.

21. A non-transitory computer-readable storage medium comprising instructions that, when executed, cause a processor of an egress network device of a network path to:
receive a packet including data indicative of a maximum transmission unit (MTU) for the network path;
form, from the first packet, a second packet to include a path header corresponding to the network path such that the path header includes the data indicative of the MTU for the network path, wherein the instructions that cause the processor to form the second packet comprise instructions that cause the processor to:
set a value of at least one bit of a first set of bits of the path header to a value indicating that the second packet includes the data indicative

Assignees

• Juniper Networks Inc

Inventors

• Singh Prashant
• Neelam Sairam

Classifications

• H04L69/22

  Parsing or analysis of headers · CPC title

• H04L47/365 Primary

  Dynamic adaptation of the packet size · CPC title

• H04L12/46

  Interconnection of networks · CPC title

• H04L12/4633

  Interconnection of networks using encapsulation techniques, e.g. tunneling · CPC title