Hi Team , please specify which VLAN ID to use while configuring private peering in azure portal for ExpressRoute. Service providers already using 2 differentVLAN IDs for primary & secondary circuits, shall we use one of them ? Or use new one ? Who will provide this new VLAN then

Hello @Ramesh Kasver , Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well. You can use any valid number as the VLAN ID to establish the peering (such as 5, 100, 152 etc). For both Primary and Secondary links you must use the same VLAN ID. This VLAN ID configured by you in the Azure portal is called C-tag or customer tag because it is customer defined. NOTE: Make sure that no other peering in the circuit uses the same VLAN ID. 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.

Hi, I need some help. We deployed expressroute and the status presently shows enabled and provisioned. Also we created gateway and virtual network mapped to VM. My questions are below what else do we need to do for the Azure vm connected to the expressroute vnet to communicate with the on prem is there any worry if gateway was created after expressroute was provisioned? although the gateway showing succeeded. presently in expressroute, we can see private peering with /30 Do we need to speak with the service provider to do the routing for us? Thanks as I look forward to responses.

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GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-11-23T09:37:52.413+00:00

Hello @Ramesh Kasver ,

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

You can use any valid number as the VLAN ID to establish the peering (such as 5, 100, 152 etc). For both Primary and Secondary links you must use the same VLAN ID. This VLAN ID configured by you in the Azure portal is called C-tag or customer tag because it is customer defined.

NOTE: Make sure that no other peering in the circuit uses the same VLAN ID.

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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Ramesh Kasver 21 Reputation points

2021-11-23T12:34:09.787+00:00

Hi Gita,

Thanks for your support !!!

One query in this line , do we need to share this VLAN ID (created in azure portal) to service provider/on premises network, in case they need to configure anything using this VLAN ID for there purpose, if any.

Thanks !

GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-11-23T13:40:25.537+00:00

@Ramesh Kasver , yes, you need to share the configured VLAN ID and s-key of the Expressroute circuit with your service provider for them to configure it in the routers. The VLAN ID configured on the portal should match with the ones configured in the routers for the Expressroute ARP (Address Resolution Protocol) to come UP.

Ramesh Kasver 21 Reputation points

2021-11-23T14:11:31.58+00:00

Hi Gita,

Thanks for the reply.
One more thing, in defining private peering(in azure portal) we get option to define only 1 VLAN ID for both primary and secondary subnets, however at layer 2 different VLAN IDs are required one each for primary & secondary circuits. Are these VLAN IDs at service provider end/on premises different than the one we define in azure portal or same ? If these are same, then which VLAN to use in azure portal as at layer 2, two different VLAN IDs are used. Please suggest if we are missing something here.

Thanks !

GitaraniSharma-MSFT 49,171 Reputation points Microsoft Employee

2021-11-23T14:27:56.207+00:00

@Ramesh Kasver , the VLAN IDs defined by you in the Azure portal are different than the VLAN IDs at service provider end. The ones defined by you in the portal are the inner tags called customer tag (c-tag) and the ones at service provider ends are the outer tags or service provider tag (s-tag). The VLAN IDs configured by you in the portal must be same for both Primary and Secondary links (this is for the routing domain/peering and not for the circuit).

aheilmaier 1 Reputation point

2022-07-20T12:46:40.283+00:00

thank's for clarification:

As I got a vlan id from my provider I thought it has to be the same vlan id on azure expressroute connection.

I parsed the API data from my provider and I can see my aSide port is a DOT1Q Port and the azure port zSide is a Q-in-Q port with STag and my choosen CTag.
{
"type": "DOT1Q",
"vlanTag": 101
}
{
"type": "DOT1Q",
"vlanTag": 102
}
{
"type": "QINQ",
"vlanSTag": 119,
"vlanCTag": 119
}
{
"type": "QINQ",
"vlanSTag": 119,
"vlanCTag": 119
}

So I can freely take vlan id 2-4094 for vlanCTag but need to use the same vlan id when using primary/secondary expressroute redundancy.
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