Merge pull request #98685 from cherylmc/patch-4

Update expressroute-howto-coexist-resource-manager.md

Author: PRMerger18

articles/expressroute/expressroute-howto-coexist-resource-manager.md

@@ -6,7 +6,7 @@ author: charwen
 
 ms.service: expressroute
 ms.topic: conceptual
-ms.date: 07/01/2019
+ms.date: 12/11/2019
 ms.author: charwen
 ms.custom: seodec18
 
@@ -37,6 +37,7 @@ The steps to configure both scenarios are covered in this article. This article
 * **Only route-based VPN gateway is supported.** You must use a route-based [VPN gateway](../vpn-gateway/vpn-gateway-about-vpngateways.md). You also can use a route-based VPN gateway with a VPN connection configured for 'policy-based traffic selectors' as described in [Connect to multiple policy-based VPN devices](../vpn-gateway/vpn-gateway-connect-multiple-policybased-rm-ps.md).
 * **Static route should be configured for your VPN gateway.** If your local network is connected to both ExpressRoute and a Site-to-Site VPN, you must have a static route configured in your local network to route the Site-to-Site VPN connection to the public Internet.
 * **VPN Gateway defaults to ASN 65515 if not specified.** Azure VPN Gateway supports the BGP routing protocol. You can specify ASN (AS Number) for a virtual network by adding the -Asn switch. If you don't specify this parameter, the default AS number is 65515. You can use any ASN for the configuration, but if you select something other than 65515, you must reset the gateway for the setting to take effect.
+* **The gateway subnet must be /27 or a shorter prefix**, (such as /26, /25), or you will receive an error message when you add the ExpressRoute virtual network gateway.
 
 ## Configuration designs
 ### Configure a Site-to-Site VPN as a failover path for ExpressRoute