BGP private peering with secondary subnet

sivakumar sivaraman 1

We have bgp private peering only with primary subnet in expressroute to our DC1, is it possible to create bgp private peering on secondary subnet to DC2 with single ER circuit

KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2023-01-11T17:21:31.54+00:00

Hi @sivakumar sivaraman ,

Just checking in to see if the below answer helped. If this answers your query, please don’t forget to click "Accept the answer" and Up-Vote for the same, which might be beneficial to other community members reading this thread. And, if you have any further query do let us know.

Thanks,

Kapil
Achira Perera 0 Reputation points

2023-12-02T11:42:37.55+00:00
Hello @KapilAnanth-MSFT

We are trying to configure private peering for the express route link. The provider gave us a single tag link without redundancy. However, I am running into the following problem when I am attempting to establish a BGP peer to our secondary subnet.

Our Edge router doesn't support subinterfaces and it only supports SVIs

Is it necessary to have a secondary peer established between the secondary subnets? can we still establish a peer to our primary subnet and route traffic?
KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2023-12-06T09:19:25.5966667+00:00

Achira Perera ,

You can use a single Connection and continue to send and receive traffic.

However, this means you do not provide you redundancy and you must set up both BGP sessions for the availability SLA to be valid.

Cheers,

Kapil

2 answers

suvasara-MSFT 10,026 Reputation points

2023-01-05T06:42:09.667+00:00

@sivakumar sivaraman , An ExpressRoute circuit can have any one, two, or all three peering's enabled per ExpressRoute circuit.

Each circuit has a fixed bandwidth (50 Mbps, 100 Mbps, 200 Mbps, 500 Mbps, 1 Gbps, 10 Gbps) and is mapped to a connectivity provider and a peering location. The bandwidth you select is shared across all circuit peerings.

All you need to have here for multiple peering's is a unique address range for DC2 subnet.
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sivakumar sivaraman 1 Reputation point

2023-01-05T07:18:25.637+00:00

Hi Suvasara,
Thank you for replay.

In our Azure ER we have two virtual circuit, one VC is peered with DC1 with BGP.So my query is can i use the other VC in the same ER for connecting (peering) to DC2. one more query: Is the primary subnet and secondary subnet are in active-active mode?

suvasara-MSFT 10,026 Reputation points

2023-01-05T09:27:35.337+00:00

@sivakumar sivaraman , What do you mean by virtual circuits here? I am assuming that you have an ER circuit connected between Azure Edge and your DC1 which needs two subnet configurations while setup. Are you trying to use that secondary subnet config to point to DC2? If so, let us know about the physical connections of DC2. A visual diagram of your architecture would help here. Can you provide?
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KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2023-01-05T06:44:33.473+00:00
Hi @sivakumar sivaraman ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.
I understand that you would like to know if we can use the secondary subnet to establish a BGP Private peering with a separate Data Center.

ExpressRoute uses a private connectivity between Azure and your DC1.

However, from the same circuit, a private connectivity towards your DC2 would not exist.

Without an underlying private path, we cannot establish a BGP session between DC2 and Azure.

You will be required to create a new circuit to establish connectivity between Azure and DC2.

Cheers,
Kapil

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sivakumar sivaraman 1 Reputation point

2023-01-05T07:40:00.173+00:00

we have two virtual circuit, one VC is peered with DC1 with BGP.So my query is can i use the other VC in the same ER for connecting (peering) to DC2. one more query: Is the primary subnet and secondary subnet are in active-active mode?

KapilAnanth-MSFT 39,211 Reputation points Microsoft Employee

2023-01-05T12:09:56.593+00:00

Hi @sivakumar sivaraman ,

I am afraid I did not understand what you refer by "virtual circuit".

An ExpressRoute circuit represents a logical connection between a single on-premises infrastructure and Microsoft cloud services through a connectivity provider.

A single ExpressRoute circuit consists of two connections, one primary and one secondary.

The primary subnet is used to provide network configuration for Primary connection. Same goes for secondary subnet.

By default, they are active - active, but you can choose not to send/receive traffic via a connection and make it active - passive.

If you can provide more details on "virtual circuit" or provide a visual architecture on what you are trying to achieve, we can assist you further

Cheers,
Kapil

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BGP private peering with secondary subnet

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