what is the actual meaning of Layer 3 connectivity and Redundancy in azure Expessroute?

Khushboo Kumari 92 Reputation points


I want to know about the Layer 3 connectivity and Redundancy in azure Expessroute. What it is and what is the exact meaning of this below sentence

Each ExpressRoute circuit consists of two connections to two Microsoft Enterprise edge routers (MSEEs) at an ExpressRoute Location from the connectivity provider or your network edge. and how its works in a simple terms. Actually I am new on it and I have no idea how its work? can you please help on this.


Azure ExpressRoute
Azure ExpressRoute
An Azure service that provides private connections between Azure datacenters and infrastructure, either on premises or in a colocation environment.
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  1. GitaraniSharma-MSFT 42,511 Reputation points Microsoft Employee

    Hello @Khushboo Kumari ,

    Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

    I understand that you would like to know what does the Layer 3 connectivity and Redundancy in Azure ExpressRoute mean.

    Layer 3 connectivity:

    Network layer is layer 3 of OSI Model. Layer 3 provides the network’s routing and switching technologies that create logical paths known as virtual circuits (VC), which are used for the transmission of data between network nodes. The main functions of Layer 3 include routing and forwarding.

    Layer 3: https://osi-model.com/network-layer/

    BGP: https://en.wikipedia.org/wiki/Border_Gateway_Protocol

    Microsoft uses BGP, an industry standard dynamic routing protocol, to exchange routes between your on-premises network, your instances in Azure, and Microsoft public addresses. We establish multiple BGP sessions with your network for different traffic profiles.

    Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-introduction#layer-3-connectivity



    ExpressRoute is designed for high availability to provide carrier grade private network connectivity to Microsoft resources. In other words, there's no single point of failure in the ExpressRoute path within Microsoft network. There are 2 connections - Primary and Secondary for to maintain the redundancy of the ExpressRoute circuit throughout the end-to-end network.

    User's image

    Microsoft network is configured to operate the primary and secondary connections of ExpressRoute circuits in active-active mode.

    To improve high availability, it's recommended to operate both the connections of an ExpressRoute circuit in active-active mode. If you let the connections operate in active-active mode, Microsoft network loads balance the traffic across the connections on per-flow basis.

    Running the primary and secondary connections of an ExpressRoute circuit in active-passive mode face the risk of both the connections failing following a failure in the active path.

    Refer: https://learn.microsoft.com/en-us/azure/expressroute/designing-for-high-availability-with-expressroute

    Kindly let us know if the above helps or you need further assistance on this issue.

    Please "Accept the answer" if the information helped you. This will help us and others in the community as well.

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