Update FAQ to reflect prefix limits

Author: jaredr80

articles/expressroute/expressroute-faqs.md

@@ -46,7 +46,15 @@ Yes. An ExpressRoute circuit, once set up, allows you to access services within
 
 ### How are VNets advertised on ExpressRoute Private Peering?
 
-The ExpressRoute gateway will advertise the *Address Space* of the Azure VNet, you can't include/exclude at the subnet level. It is always the VNet Address Space that is advertised. Also, if VNet Peering is used and the peered VNet has "Use Remote Gateway" enabled, the Address Space of the peered VNet will also be advertised.
+The ExpressRoute gateway will advertise the *Address Space(s)* of the Azure VNet, you can't include/exclude at the subnet level. It is always the VNet Address Space that is advertised. Also, if VNet Peering is used and the peered VNet has "Use Remote Gateway" enabled, the Address Space of the peered VNet will also be advertised.
+
+### How many prefixes can be advertised from a VNet to on-premises on ExpressRoute Private Peering?
+
+There is a maximum of 200 prefixes advertised on a single ExpressRoute connection, or through VNet peering using gateway transit. For example, if you have 199 address spaces on a single VNet connected to an ExpressRoute circuit, all 199 of those prefixes will be advertised to on-premises. Alternatively, if you have a VNet enabled to allow gateway transit with 1 address space and 150 spoke VNets enabled using the "Allow Remote Gateway" option, the VNet deployed with the gateway will advertise 151 prefixes to on-premises.
+
+### What happens if I exceed the prefix limit on an ExpressRoute connection?
+
+The connection between the ExpressRoute circuit and the gateway (and peered VNets using gateway transit, if applicable) will go down. It will re-establish when the prefix limit is no longer exceeded.  
 
 ### Can I filter routes coming from my on-premises network?