Layer-3 Router Address Resolution Cache for Datacenter Scaling
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Solution Overview
Problem
Current technologies for scaling layer-2 domains over layer-3 connections, such as FabricPath and OTV, face inefficiencies due to large MAC address tables and excessive ARP flooding, leading to high hardware costs and traffic congestion.
Innovation Solution
Implementing a layer-3 router with an address resolution cache that stores host network addresses, hardware addresses, and switch identifiers, and using ARP caches to intercept and respond to address resolution requests, thereby reducing the need for layer-2 flooding and conserving hardware memory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional OTV builds and maintains MAC address tables in ASIC hardware memory, then layer-2 connectivity across domains is achieved, but hardware cost and memory consumption increase prohibitively
Solution Approach 1:
The patent extracts the MAC address table functionality from expensive ASIC hardware memory and relocates it to cheaper software-based data structures in general-purpose memory. The routing table in the layer-3 router now stores MAC address to switch ID mappings, eliminating the need for dedicated hardware memory tables in ASICs.
Solution Approach 2:
The patent introduces a layer-3 router as an intermediary between layer-2 domains. This router maintains MAC address tables and performs address resolution, acting as a mediator that translates layer-2 MAC addresses to layer-3 switch IDs. This intermediary approach allows MAC address information to be stored in software rather than requiring expensive hardware memory at every switch.
2Area of stationary object
If layer-2 domains are scaled by connecting multiple datacenters over layer-3 networks, then domain coverage is improved, but ARP flooding and traffic congestion increase
Solution Approach 1:
The patent performs preliminary address resolution by having the layer-3 router build and maintain MAC address tables in advance using control plane protocols. When a layer-2 frame needs to be forwarded to another domain, the router already has the destination MAC address mapped to the appropriate switch ID, eliminating the need for ARP flooding across domains.
Solution Approach 2:
The patent implements feedback mechanisms where the layer-3 router learns MAC address to switch ID mappings from control plane advertisements and updates its routing table accordingly. This feedback loop allows the router to maintain accurate address information without requiring broadcast-based ARP protocols across layer-3 boundaries.
3Adaptability or versatility
If boundary devices store large amounts of MAC address information, then address resolution capability is improved, but device complexity and cost increase
Solution Approach 1:
The layer-3 router serves as an intermediary that centralizes MAC address table storage and management. Instead of requiring every boundary switch to maintain large MAC address tables, the routing table in the layer-3 router consolidates this information, reducing complexity at individual boundary devices while maintaining overall address resolution capability.
Solution Approach 2:
The patent uses control plane protocols to distribute and synchronize MAC address to switch ID mapping information across the network. Rather than storing complete MAC tables at every boundary device, each device receives relevant routing information through control plane advertisements, creating lightweight local copies of necessary address information.
Data Source
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AI summary
In one embodiment, a method includes building an address resolution cache for a layer-3 router in a first layer-2 datacenter, where the address resolution cache includes a plurality of entries, each of the entries containing a host network address, a host hardware address, and a switch identifier for a switch serving a host, intercepting an address resolution flood within the first layer-2 datacenter that seeks address resolution for a host in a second layer-2 datacenter, and generating a response to the address resolution flood that indicates a source in the second layer-2 datacenter, where data indicating the source in the second layer-2 datacenter is accessed from the address resolution cache.