Connect Two active DC to Azure Express Route

Question

Connect Two active DC to Azure Express Route

Rajesh C S 0

Our setup includes DC1 and DC2 configured for high availability. Both data centres need to connect to Azure resources deployed in Germany West Central, as well as to a disaster recovery (DR) site in Germany North. Please refer to the attached diagram for details on the network flow. Both DC1 and DC2 are connected to the same ISP. Kindly advise on the number of ExpressRoute connections required for each Azure region to ensure active connectivity from both DC1 and DC2.

Please suggest an appropriate network design for this scenario.

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Answer 1

Vinodh247-1375 44,716 Volunteer Moderator

Hi ,

Thanks for reaching out to Microsoft Q&A.

You do not need separate ExpressRoute circuits per data centre. Design this as a highly available, active-active ExpressRoute architecture.

Provision one ExpressRoute circuit per Azure region (one for Germany West Central and one for Germany North). Each circuit already provides built-in redundancy with dual Microsoft edge routers. From your side, connect both DC1 and DC2 to the same ExpressRoute circuit via your ISP using private peering, ensuring both DCs advertise routes using BGP. Since both DCs share the same ISP, the ISP should provide dual connectivity paths (or diverse CPE links) into the ExpressRoute circuit so that both DC1 and DC2 remain active.

For resilience and failover, configure active-active routing using BGP with proper AS path prepending or local preference, so both DCs can simultaneously send traffic while also providing failover capability if one DC goes down. Repeat the same setup for the DR region (Germany North), ideally with a separate ExpressRoute circuit to isolate failure domains.

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Rajesh C S 0 Reputation points

2026-05-07T08:57:26.2266667+00:00

@Vinodh247-1375 thanks for the response . As per your comments I prepared a high level design could you please review and let me know if my understanding is correct .

Settings in ER:

On-prem DC Network team action
advertise routes using BGP
Vinodh247-1375 44,716 Reputation points Volunteer Moderator

2026-05-09T01:59:12.71+00:00

Yes, “advertise routes using BGP” is correct, but the real design success depends on how you manipulate BGP attributes and ensure ISP-level redundancy. Without that, the setup will work, but not reliably under failure.

Answer 2

Hello @Rajesh C S,

Thank you for reaching out to Microsoft Q&A.

it sounds like you’ve got two always-on data centers (DC1 and DC2) that both need low-latency, highly available connectivity into West Central Germany (primary) and Germany North (DR). Here’s how you can design it:

Use Active-Active ExpressRoute circuits

Every ExpressRoute circuit comes with two physical connections (to two Microsoft edge routers) that you can run in active-active mode. This allows per-flow load-balancing and automatic failover.
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See “Operate your ExpressRoute circuit connections in active-active mode” for details: https://docs.microsoft.com/azure/expressroute/designing-for-high-availability-with-expressroute#active-active-connections

Two separate circuits (recommended for maximum resiliency)

• Circuit #1 in West Central Germany

• Circuit #2 in Germany North

• Each circuit has two provider hand-offs in active-active mode.

• Both DC1 and DC2 peer to both circuits (four BGP sessions per DC).

• You can use BGP prefix-filtering or AS-path prepending to steer “primary” traffic to West Central and “DR” traffic to Germany North.

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Reference:

ExpressRoute premium add-on overview https://learn.microsoft.com/azure/expressroute/expressroute-introduction#expressroute-premium-add-on
Link virtual network to an ExpressRoute circuit https://docs.microsoft.com/azure/expressroute/expressroute-howto-linkvnet-portal-resource-manager

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