DHCP Response Forwarding via Border Device in Stretched Fabric Networks

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Solution Overview

Problem

Conventional fabric networks struggle to forward Dynamic Host Configuration Protocol (DHCP) response packets to an anycast relay agent IP address in the EID space, especially in stretched Layer-2 environments, as they cannot distinguish between endpoints on the same subnet across multiple Fabric Edge (FE) devices.

Innovation Solution

The solution involves a border device extracting the client MAC address from the DHCP response packet, querying a map server to resolve the locator address, and then encapsulating the packet for forwarding to the correct FE device, ensuring accurate delivery of DHCP responses in the EID space.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional fabric networks use anycast relay agent IP address in EID space for DHCP forwarding, then network flexibility and stretched Layer-2 functionality are improved, but the ability to distinguish between endpoints on the same subnet across multiple FE devices deteriorates

Engineering Contradiction:

Improvenetwork flexibilityVSAvoidendpoint distinction accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The border device acts as an intermediary between the DHCP server and FE devices. It receives DHCP response packets destined for the anycast relay agent IP address, extracts the client MAC address, queries the map server to resolve the locator address, and forwards the packet to the correct FE device. This intermediary function resolves the contradiction by enabling anycast-based flexibility while maintaining precise endpoint distinction through the border device's packet handling logic.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The solution introduces a new dimension of operation by implementing DHCP response forwarding at the border device level rather than relying solely on standard IP routing within the EID space. This dimensional shift allows the network to maintain anycast gateway IP addresses for flexibility while adding a border device processing layer that provides precise endpoint distinction through map server lookups based on client MAC addresses.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Device complexity

If DHCP response packets are forwarded using standard IP routing in EID space, then routing simplicity is improved, but successful delivery to the correct FE device in stretched Layer-2 environments deteriorates

Engineering Contradiction:

Improverouting complexityVSAvoidpacket delivery success

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The border device serves as a mediator that bridges standard IP routing and precise packet delivery. It receives DHCP response packets that would normally be routed using standard IP routing in the EID space, but instead intercepts these packets, performs map server lookups to determine the correct FE device, and forwards them appropriately. This maintains routing simplicity for most traffic while ensuring reliable delivery for DHCP responses in stretched Layer-2 environments.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If the network uses stretched Layer-2 environments across multiple FE devices, then network scalability and flexibility are improved, but the ability to forward DHCP responses to the correct FE device deteriorates

Engineering Contradiction:

Improvenetwork scalabilityVSAvoidDHCP response forwarding

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The solution segments the DHCP response forwarding function from standard IP routing by implementing it at the border device level. This segmentation allows stretched Layer-2 environments to maintain their scalability and flexibility while the border device handles the specialized DHCP response forwarding logic. The segmentation isolates the complexity of DHCP response handling in stretched Layer-2 environments from the rest of the routing infrastructure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The border device acts as an intermediary that simplifies DHCP response forwarding in stretched Layer-2 environments. It receives DHCP responses, performs map server lookups to resolve the correct FE device based on client MAC addresses, and forwards packets accordingly. This intermediary function maintains network scalability and flexibility while automating the DHCP response forwarding process that would otherwise be complex in stretched Layer-2 environments.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS10432578B2Client address based forwarding of dynamic host configuration protocol response packets

Publication Date: 2019.10.01 CISCO TECHNOLOGY INC

AI summary

Client address based forwarding of dynamic host configuration protocol response packets may be provided. First, a first relay agent on a first network device may receive a first discovery message associated with a first client device. The first discovery message may include a first discovery message identifier field comprising a first identifier corresponding to the first client device. The first client device may be associated with a subnet. Then the first relay agent may register, with a map server, the first identifier with an address of the first network device and add a gateway address corresponding to the first relay agent to the first discovery message. Next, the first relay agent may encapsulate the first discovery message and forward the encapsulated first discovery message over a network to a border device.