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setting up azure Express route Private peerting issue

Pravendra Rajput 56 Reputation points
2022-07-28T11:47:33.973+00:00

While setting up Express route over private peering, and getting it enabled at ISP end, our ISP told the below:
We provisioned the ExpressRoute and configured private peering. The Private peering is using 1xx.x.x/30 and 1xx.x.x/30, but we cannot see Microsoft ARP in Private Peering ARP table, and we cannot ping 1xx.x.x.2 from 1x.x.0x.1.

how to resolve this issue?
We see express route circuit in azure as provisioned.

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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Answer accepted by question author

GitaraniSharma-MSFT 50,197 Reputation points Microsoft Employee Moderator
2022-07-29T09:39:18.467+00:00

Hello @RajputPravendra-1326 ,

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

I understand that you are facing ARP issue when configuring private peering over Azure ExpressRoute.

Address Resolution Protocol (ARP) is a layer 2 protocol used to map the Ethernet address (MAC address) with an ip address. ARP tables can help validate layer 2 configuration and troubleshooting basic layer 2 connectivity issues.

Please refer the below doc to get the ARP table for your ExpressRoute circuit:
https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-arp-resource-manager

ARP issue can occur at either the on-prem/ISP side or Microsoft side.

If a problem with the ISP occurs, the ARP table will show one of two things. You'll either see the on-premises MAC address show incomplete or only see the Microsoft entry in the ARP table. You need to contact your ISP to debug such issues.
Refer : https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-arp-resource-manager#arp-table-when-on-premises--connectivity-provider-side-has-problems

But if your ISP is stating that they cannot see Microsoft ARP, validate this once by getting the ARP table output.
Refer : https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-arp-resource-manager#arp-table-when-microsoft-side-has-problems

If Microsoft side has issues with ARP, you won't see an ARP table shown for a peering.
In such case, you need to open a support ticket with Microsoft support specifying that you have an issue with layer 2 connectivity. Hence, if you have a support plan, I request you file a support ticket, else please do let us know, we will try and help you get a one-time free technical support.

NOTE : If layer 3 is provided by your ISP and the ARP tables are blank in the output of the table you received by running the PowerShell command, refresh the Circuit configuration using the refresh button on the portal. This operation will apply the right routing configuration on your circuit.

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

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