ExpressRoute routing requirements

To connect to Microsoft cloud services using ExpressRoute, you’ll need to set up and manage routing. Some connectivity providers offer setting up and managing routing as a managed service. Check with your connectivity provider to see if they offer this service. If they don't, you must adhere to the following requirements:

Refer to the Circuits and routing domains article for a description of the routing sessions that need to be set up in to facilitate connectivity.


Microsoft does not support any router redundancy protocols (for example, HSRP, VRRP) for high availability configurations. We rely on a redundant pair of BGP sessions per peering for high availability.

IP addresses used for peerings

You need to reserve a few blocks of IP addresses to configure routing between your network and Microsoft's Enterprise edge (MSEEs) routers. This section provides a list of requirements and describes the rules regarding how these IP addresses must be acquired and used.

IP addresses used for Azure private peering

You can use either private IP addresses or public IP addresses to configure the peerings. The address range used for configuring routes must not overlap with address ranges used to create virtual networks in Azure.

  • You must reserve a /29 subnet or two /30 subnets for routing interfaces.
  • The subnets used for routing can be either private IP addresses or public IP addresses.
  • The subnets must not conflict with the range reserved by the customer for use in the Microsoft cloud.
  • If a /29 subnet is used, it will be split into two /30 subnets.
    • The first /30 subnet is used for the primary link and the second /30 subnet is used for the secondary link.
    • For each of the /30 subnets, you must use the first IP address of the /30 subnet on your router. Microsoft uses the second IP address of the /30 subnet to set up a BGP session.
    • You must set up both BGP sessions for our availability SLA to be valid.

Example for private peering

If you choose to use a.b.c.d/29 to set up the peering, it will be split into two /30 subnets. In the example below, we look at how the a.b.c.d/29 subnet is used.

a.b.c.d/29 will be split to a.b.c.d/30 and a.b.c.d+4/30 and passed down to Microsoft through the provisioning APIs. You will use a.b.c.d+1 as the VRF IP for the Primary PE and Microsoft will consume a.b.c.d+2 as the VRF IP for the primary MSEE. You will use a.b.c.d+5 as the VRF IP for the secondary PE and Microsoft will use a.b.c.d+6 as the VRF IP for the secondary MSEE.

Consider a case where you select to set up private peering. includes addresses from to, among which:

  • will be assigned to link1, with provider using and Microsoft using
  • will be assigned to link2, with provider using and Microsoft using

IP addresses used for Azure public and Microsoft peering

You must use public IP addresses that you own for setting up the BGP sessions. Microsoft must be able to verify the ownership of the IP addresses through Routing Internet Registries and Internet Routing Registries.

  • You must use a unique /29 subnet or two /30 subnets to set up the BGP peering for each peering per ExpressRoute circuit (if you have more than one).
  • If a /29 subnet is used, it will be split into two /30 subnets.
    • The first /30 subnet will be used for the primary link and the second /30 subnet is used for the secondary link.
    • For each of the /30 subnets, you must use the first IP address of the /30 subnet on your router. Microsoft uses the second IP address of the /30 subnet to set up a BGP session.
    • You must set up both BGP sessions for our availability SLA to be valid.

Public IP address requirement

Private peering

You can choose to use public or private IPv4 addresses for private peering. We provide end-to-end isolation of your traffic, so overlapping of addresses with other customers is not possible in case of private peering. These addresses are not advertised to Internet.

Public peering

The Azure public peering path enables you to connect to all services hosted in Azure over their public IP addresses. These include services listed in the ExpessRoute FAQ and any services hosted by ISVs on Microsoft Azure. Connectivity to Microsoft Azure services on public peering is always initiated from your network into the Microsoft network. You must use Public IP addresses for the traffic destined to Microsoft network.

Microsoft peering

The Microsoft peering path lets you connect to Microsoft cloud services that are not supported through the Azure public peering path. The list of services includes Office 365 services, such as Exchange Online, SharePoint Online, Skype for Business, and Dynamics 365. Microsoft supports bi-directional connectivity on the Microsoft peering. Traffic destined to Microsoft cloud services must use valid public IPv4 addresses before they enter the Microsoft network.

Make sure that your IP address and AS number are registered to you in one of the following registries:


Public IP addresses advertised to Microsoft over ExpressRoute must not be advertised to the Internet. This may break connectivity to other Microsoft services. However, Public IP addresses used by servers in your network that communicate with O365 endpoints within Microsoft may be advertised over ExpressRoute.

Dynamic route exchange

Routing exchange will be over eBGP protocol. EBGP sessions are established between the MSEEs and your routers. Authentication of BGP sessions is not a requirement. If required, an MD5 hash can be configured. See the Configure routing and Circuit provisioning workflows and circuit states for information about configuring BGP sessions.

Autonomous System numbers

Microsoft will use AS 12076 for Azure public, Azure private and Microsoft peering. We have reserved ASNs from 65515 to 65520 for internal use. Both 16 and 32 bit AS numbers are supported.

There are no requirements around data transfer symmetry. The forward and return paths may traverse different router pairs. Identical routes must be advertised from either sides across multiple circuit pairs belonging you. Route metrics are not required to be identical.

Route aggregation and prefix limits

We support up to 4000 prefixes advertised to us through the Azure private peering. This can be increased up to 10,000 prefixes if the ExpressRoute premium add-on is enabled. We accept up to 200 prefixes per BGP session for Azure public and Microsoft peering.

The BGP session will be dropped if the number of prefixes exceeds the limit. We will accept default routes on the private peering link only. Provider must filter out default route and private IP addresses (RFC 1918) from the Azure public and Microsoft peering paths.

Transit routing and cross-region routing

ExpressRoute cannot be configured as transit routers. You will have to rely on your connectivity provider for transit routing services.

Advertising default routes

Default routes are permitted only on Azure private peering sessions. In such a case, we will route all traffic from the associated virtual networks to your network. Advertising default routes into private peering will result in the internet path from Azure being blocked. You must rely on your corporate edge to route traffic from and to the internet for services hosted in Azure.

To enable connectivity to other Azure services and infrastructure services, you must make sure one of the following items is in place:

  • Azure public peering is enabled to route traffic to public endpoints
  • You use user-defined routing to allow internet connectivity for every subnet requiring Internet connectivity.

Advertising default routes will break Windows and other VM license activation. Follow instructions here to work around this.

Support for BGP communities

This section provides an overview of how BGP communities will be used with ExpressRoute. Microsoft will advertise routes in the public and Microsoft peering paths with routes tagged with appropriate community values. The rationale for doing so and the details on community values are described below. Microsoft, however, will not honor any community values tagged to routes advertised to Microsoft.

If you are connecting to Microsoft through ExpressRoute at any one peering location within a geopolitical region, you will have access to all Microsoft cloud services across all regions within the geopolitical boundary.

For example, if you connected to Microsoft in Amsterdam through ExpressRoute, you will have access to all Microsoft cloud services hosted in North Europe and West Europe.

Refer to the ExpressRoute partners and peering locations page for a detailed list of geopolitical regions, associated Azure regions, and corresponding ExpressRoute peering locations.

You can purchase more than one ExpressRoute circuit per geopolitical region. Having multiple connections offers you significant benefits on high availability due to geo-redundancy. In cases where you have multiple ExpressRoute circuits, you will receive the same set of prefixes advertised from Microsoft on the public peering and Microsoft peering paths. This means you will have multiple paths from your network into Microsoft. This can potentially cause sub-optimal routing decisions to be made within your network. As a result, you may experience sub-optimal connectivity experiences to different services. You can rely on the community values to make appropriate routing decisions to offer optimal routing to users.

Microsoft Azure region BGP community value
North America
East US 12076:51004
East US 2 12076:51005
West US 12076:51006
West US 2 12076:51026
West Central US 12076:51027
North Central US 12076:51007
South Central US 12076:51008
Central US 12076:51009
Canada Central 12076:51020
Canada East 12076:51021
South America
Brazil South 12076:51014
North Europe 12076:51003
West Europe 12076:51002
UK South 12076:51024
UK West 12076:51025
Asia Pacific
East Asia 12076:51010
Southeast Asia 12076:51011
Japan East 12076:51012
Japan West 12076:51013
Australia East 12076:51015
Australia Southeast 12076:51016
India South 12076:51019
India West 12076:51018
India Central 12076:51017
Korea South 12076:51028
Korea Central 12076:51029

All routes advertised from Microsoft will be tagged with the appropriate community value.


Global prefixes will be tagged with an appropriate community value and will be advertised only when ExpressRoute premium add-on is enabled.

In addition to the above, Microsoft will also tag prefixes based on the service they belong to. This applies only to the Microsoft peering. The table below provides a mapping of service to BGP community value.

Service BGP community value
Exchange Online 12076:5010
SharePoint Online 12076:5020
Skype For Business Online 12076:5030
Dynamics 365 12076:5040
Other Office 365 Online services 12076:5100

Microsoft does not honor any BGP community values that you set on the routes advertised to Microsoft.

BGP Community support in National Clouds (Preview)

National Clouds Azure Region BGP community value
US Government
US Gov Arizona 12076:51106
US Gov Iowa 12076:51109
US Gov Virginia 12076:51105
US Gov Texas 12076:51108
US DoD Central 12076:51209
US DoD East 12076:51205
Service in National Clouds BGP community value
US Government
Exchange Online 12076:5110
SharePoint Online 12076:5120
Skype For Business Online 12076:5130
Dynamics 365 12076:5140
Other Office 365 Online services 12076:5200

Next steps