NAT Source Address Translation for ISP Path Switching

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Solution Overview

Problem

Optimizing return traffic paths in network communications is challenging, especially when using multiple Internet Service Provider (ISP) connections, as changing the return path for load-balancing or addressing network issues can disrupt established Transmission Control Protocol (TCP) connections and requires significant route changes across multiple ISP networks.

Innovation Solution

Implementing a system that uses Network Address Translation (NAT) to transparently translate source addresses in outbound traffic from one ISP connection to another, allowing for dynamic switching of return traffic paths without disrupting existing TCP connections by generating and sending address mappings between different address pools associated with multiple ISP connections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the return path for inbound traffic is changed to optimize load-balancing or address network performance issues, then network performance and load distribution are improved, but the TCP connections are disrupted and route changes must be propagated across multiple ISP networks

Engineering Contradiction:

Improvenetwork performanceVSAvoidTCP connection stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces an intermediary NAT address translation mechanism that mediates between the outbound and inbound traffic paths. By translating the source address in outbound packets to a different IP address than the original host address, the system creates an intermediary mapping that allows inbound traffic to be routed through a different ISP connection without the receiving host being aware of the path change. This intermediary translation layer preserves TCP connection stability while enabling return path optimization.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the IP address parameter in the outbound traffic by performing NAT translation, where the source address is replaced with an address from a different address pool associated with another ISP connection. This parameter change enables the return traffic to take a different path through the network while maintaining compatibility with existing TCP connections, as the translation is transparent to the application layer.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If NAT translation is used to change the source address in outbound traffic, then return traffic paths can be optimized without disrupting TCP connections, but the complexity of address mapping and translation increases

Engineering Contradiction:

Improvereturn path flexibilityVSAvoidaddress translation complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent implements a universal NAT translation mechanism that can handle multiple address pools corresponding to different ISP connections. The NAT device maintains translation tables that map between original host addresses and translated addresses from different address pools, allowing a single NAT infrastructure to support flexible return path selection across multiple ISPs without requiring separate translation systems for each connection.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If multiple ISP connections are used for outbound traffic, then load-balancing and performance optimization are enabled, but the return traffic must follow the path determined by the assigned IP address which limits routing flexibility

Engineering Contradiction:

Improveload-balancing capabilityVSAvoidreturn path selection

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The patent inverts the traditional approach by changing the source address in outbound traffic rather than the destination address. Normally, routing flexibility is achieved by changing destination addresses, but this would disrupt established TCP connections. By inverting the approach and translating source addresses to different IPs from different address pools, the system enables return path flexibility while preserving connection stability, as the inversion allows the return traffic to be routed differently without affecting the original connection establishment.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9154541B2Optimizing return traffic paths using network address translation

Publication Date: 2015.10.06 CISCO TECHNOLOGY INC

AI summary

In one embodiment, an apparatus comprises logic for optimizing return traffic paths using network address translation (NAT). The logic is operable to receive outbound data from a source node in a source network, and to replace a source address in a source address field in the outbound data with a first address from a first address pool associated with a first connection. The logic is operable to determine that return traffic on the first connection needs to be switched over to a second connection, where a second address pool is associated with the second connection. The logic is operable to generate a mapping that associates the first address with a second address from the second address pool and, based on the mapping, to replace the first address in the source address field in the outbound data with the second address. The logic is also operable to send the outbound data to the destination node over the second connection.