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RAS Gateway multitenant BGP router 
When you deploy network virtualization and employ the encapsulation and isolation methods 
described earlier in this chapter, you face an interesting problem: How do the VMs in these isolated 
networks communicate outside the isolated network? How do external machines communicate with 
these isolated VMs if they needed to? 
Windows Server 2016 introduces additional capability to the RAS Gateway role to include BGP 
support. Earlier versions supported the following features for RAS Gateway: 

Site-to-site VPN 

Point-to-site VPN 

GRE tunneling 

NAT 
Given that all these features are now available in RAS Gateway, you can reap the following benefits: 

VMs can talk to other networks outside the routing domain to which they are assigned. 

You can create endpoints into the virtual network if required. 

You can connect virtual and physical networks together. 
With the introduction of BGP, new possibilities open up for our network environments. For example, 
Express route works on BGP, not to mention the Internet! 
BGP dynamically learns which networks are attached and announces these networks to other BGP-
capable routers. The other BGP-capable routers can populate their routing table with the entries, and 
if the BGP router receives a request to send traffic to a tenant’s network, it will know how to route the 
traffic appropriately. An important part of BGP is the ability to provide route redundancy and 
automatically recalculate the best route to the desired network. In that case, if you have several 
routers connected together and there were multiple paths to a desired network, BGP would work out 
the optimal route to it. Then, in the event of a failure, it would recalculate the route and announce it 
back to its BGP peers. 
One of the challenges in relation to virtualized networks and the RAS Gateway in Windows Server 
2012 is the relationship of gateways. If you want to deploy a HA pool of gateways in Windows 
Server 2012, there is no way to separate the gateway pool for separate functions or tenants. There 
are also strict placement requirements of the Gateway Nodes, which cause a lot of network problems 
in enterprise clusters. 

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CHAPTER 2 | Software-defined datacenter 
Windows Server 2016 implements a true pool model in which you can create pools for specific 
functions or mix the functions. Figure 2-69 shows how you can deploy pools for different functions.