EVPN Reachability Advertisement Using Spanning Tree Forwarding State
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Solution Overview
Problem
Network devices implementing Ethernet Virtual Private Networks (EVPN) and Spanning Tree Protocol (STP) experience undesired traffic blackholing due to advertising network reachability based on the apparent up state of Ethernet interfaces, despite the interfaces being in a non-forwarding state according to STP, leading to disruptions in traffic forwarding.
Innovation Solution
Network devices are configured to advertise network reachability information based on logical topology interface states, specifically spanning tree interface states, rather than solely on the Ethernet interface and link states, to ensure accurate traffic forwarding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If network devices advertise reachability information based on Ethernet interface up state, then reachability information is advertised promptly, but traffic blackholing occurs when spanning tree interface is in non-forwarding state
Solution Approach 1:
The patent applies preliminary action by checking the spanning tree interface state before advertising reachability information. The device determines whether the interface is in a forwarding state prior to generating EVPN route advertisements, preventing blackholing before it occurs. This advance verification ensures that reachability is only advertised when the interface can actually forward traffic.
2Reliability
If network devices use spanning tree interface state for reachability advertisement, then traffic blackholing is prevented, but advertisement timing is delayed
Solution Approach 1:
The patent applies dynamics by continuously monitoring spanning tree interface state changes and dynamically adjusting reachability advertisement timing. When the interface transitions to a forwarding state, the device promptly advertises reachability information. This dynamic response minimizes delays while ensuring reliability, as advertisements are generated as soon as the interface is ready to forward traffic.
3Device complexity
If network devices advertise reachability without checking spanning tree state, then advertisement process is simple, but loop-free topology is compromised
Solution Approach 1:
The patent applies feedback by using spanning tree protocol state information to control EVPN reachability advertisements. The spanning tree protocol provides continuous feedback about interface forwarding states, and this feedback is used to determine when to advertise or withdraw reachability information. This feedback mechanism maintains loop-free topology while enabling efficient reachability advertisement.
Data Source
AI summary
A network device may include memory circuitry and processing circuitry. The processing circuitry may be configured to obtain a spanning tree topology indicating at least one spanning tree interface state. The processing circuitry may be configured to perform reachability information advertisement based on the spanning tree interface state. In some illustrative configurations, the network device may be one of multiple multihoming network devices configured to provide an Ethernet segment and the reachability information being advertised based on the spanning tree interface state includes Ethernet Virtual Private Network (EVPN) route information.