Gateway MSS Modification for Layer Two Network Extension
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Solution Overview
Problem
The extension of layer two networks across multiple computing sites faces challenges due to packet size issues related to the maximum transmission unit (MTU), particularly caused by encapsulation, which can lead to fragmentation and undelivered packets.
Innovation Solution
Gateways at computing sites modify the maximum segment size (MSS) option of packets to a maximum value, ensuring they comply with MTU criteria, and encapsulate or decapsulate packets as necessary to prevent fragmentation and ensure successful communication across sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If gateways encapsulate packets to extend layer two networks across multiple computing sites, then virtual nodes can communicate over the same broadcast domain, but packet size exceeds MTU causing fragmentation and undelivered packets
Solution Approach 1:
The gateway performs preliminary action by modifying the MSS option in TCP packets before encapsulation. This pre-modification ensures that the encapsulated packet will not exceed the MTU of the underlying network, preventing fragmentation and ensuring reliable delivery across the extended layer two network.
Solution Approach 2:
The gateway changes the MSS parameter in the TCP option field of the packet. By modifying this parameter to reflect the reduced available buffer size after encapsulation, the gateway ensures that the packet size adapts to the MTU constraints of the transport network, thereby preventing fragmentation and maintaining packet delivery reliability.
2Reliability
If gateways modify MSS options to prevent fragmentation, then packet delivery reliability improves, but additional packet processing steps are required
Solution Approach 1:
The gateway performs self-service by automatically detecting the MTU of the underlying network and adjusting the MSS option accordingly. This automated process eliminates the need for manual configuration or complex fragment reassembly logic, reducing gateway processing complexity while maintaining high packet delivery reliability.
3Adaptability or versatility
If encapsulation is used to extend the network, then virtual nodes can communicate across sites, but the packet size increases beyond standard MTU limits
Solution Approach 1:
The gateway performs preliminary action by modifying the MSS option in TCP packets before encapsulation. This pre-modification ensures that the encapsulated packet will not exceed the MTU of the underlying network, preventing fragmentation and ensuring reliable delivery across the extended layer two network.
Solution Approach 2:
The gateway changes the MSS parameter in the TCP option field of the packet. By modifying this parameter to reflect the reduced available buffer size after encapsulation, the gateway ensures that the packet size adapts to the MTU constraints of the transport network, thereby preventing fragmentation and maintaining packet delivery reliability.
Data Source
AI summary
Described herein are systems, methods, and software to manage the encapsulation of layer two communications across computing sites. In one example, a gateway at a first computing site may receive an encapsulated packet from a second gateway at a second computing site. After receiving the encapsulated packet, the gateway decapsulates the encapsulated packet and determines that the decapsulated packet satisfies MSS criteria. The gateway further, in response to determining that the decapsulated packet satisfies the MSS criteria, modifies an MSS option associated with the decapsulated packet to a maximum value and forwards the decapsulated packet to a destination virtual node in the first computing site.