Routing traffic between VNets in Azure - azure

If two vnets are connected to each other via multiple set of peering vnets, how does azure route the traffic? Fo example, lets consider the below: A, B, C, D are 5 VNets and the they are peered (bi-directionally with traffic forwarding allowed).
Now if A wants to send a packet to D, how it is determined whether it will take the A-B-C-D path or the A-E-D path?
Any docs will be helpful.

As far as I know, VNet Peering connections are non-transitive. It seems that it's still on the roadmap. See the feedback here.
From your picture, If only VNet Peering connections between them, then A could not reach D, also A could not reach C. A only could reach direct-connected B and E.
If you want to allow much VNets communication. You could implement a hub-spoke network topology in Azure. As the hub network, you could deploy a VPN gateway then enable allow gateway transit to other spoke VNets and enable use remote gateways in each spoke VNets. If you require connectivity between spokes, consider implementing an NVA for routing in the hub, and using UDR(custom routes) in the spoke to forward traffic to the hub. In this scenario, you must configure the peering connections to allow forwarded traffic.
VNet Peering enables you to connect VNets through the Azure backbone network. Azure automatically creates a route table for each subnet within an Azure VNet and adds system default routes to the table. You can also override some of Azure's system routes with custom routes.
If multiple routes contain the same address prefix, Azure selects the
route type, based on the following priority:
User-defined
route BGP route
System route
You could get more details about Virtual network traffic routing

According to this article you'd need an NVA somewhere, vnet peering is non transitive.
At the beggining of the same article they talk a bit more about this.
To sum it up. packet wont reach D from A unless you fix your networking setup

Some years ago but i think service chaining allows that as far as i understand the documentation
To enable service chaining, configure user-defined routes that point
to virtual machines in peered virtual networks as the next hop IP
address. User-defined routes could also point to virtual network
gateways to enable service chaining.

Related

How to connect overlapping VNets in Azure?

I am working on an Azure-based networking solution.
We have a typical hub and spoke VNets topology. The Hub VNet connects to on-prem DC via ExpressRoute and spoke VNets peer to Hub VNet. There is an Azure Firewall in the Hub that filters traffic between Hub-spokes and hub-on-prem segments. GREEN in the diagram
We have a bizarre requirement of adding a new isolated VNet (RED in the diagram) that will have overlapping IPs with the existing network (GREEN). We want to allow workloads in this new VNet to access private apps deployed in Hub or on-prem.
I need help on how to achieve this connectivity.
Note: We don't want to set up any VPN between the new VNet and Hub
As you might appreciate, this is more of a general networking limitation moreso than an Azure limitation. If we want two different networks with overlapping IP addresses to communicate then we would need networking devices in between both networks that perform some form of network address translation so the IP addresses appear to be different to the communicating hosts. Below is an example from the Azure documentation
Logically you have two options here:
Create your own network devices and configure routes between these subnets to transit your virtual appliance that does the translation.
Use the managed service from Azure. In this case, it's the Azure VPN Gateway
I saw your note above for not wanting to use any VPN devices. Having said that, however, generally speaking it is usually a better option from an availability & supportability perspective to leverage the built-in offering vs. hand rolling your own virtual appliance using IP tables or a Windows NAT Router or something similar. Hope this clarifies.
It is not possible to peer Virtual Networks with overlapping IP addresses. This is documented here. You will have to move to a different address space and move/recreate resources under this new address space.
If it helps you can take a look at this Checklist before moving resources.

Subnet to subnet peering in azure

We have our application and database in different VNETs in different subscription.
Also we have different environments (Pre-Production and Production).
Currently the database for PROD and PRE-PROD is in different subnet but same VNET.
I see we can have peering at VNET level.
We want the peering between the application and database at subnet level so that PRE-PROD application should not be able to connect to PROD database and vice-versa.
From Microsoft documentation:
Azure routes traffic between all subnets within a virtual network, by default. You can create your own routes to override Azure's default routing.
https://learn.microsoft.com/en-us/azure/virtual-network/tutorial-create-route-table-portal
You would want to look at network segmentation patterns. You can achieve basic microsegmentation by using Network Security Groups in Azure.
Based on your question, I assume you want to allow traffic only from one subnet into another subnet (over a peered network though, but that does not matter much) - and maybe even only allow one database port to be accessed from your application subnet - and lock everything else down.
This approach is described here: https://learn.microsoft.com/en-us/azure/architecture/framework/security/design-network-segmentation
You would want to create one NSG per subnet, make a rule to block all inbound traffic and then allow only traffic that is required. Note that NSG's are stateful, so you do not need to specify outbound rules for your traffic. Also make sure you apply the rules in the right order from top to bottom. The rule with the lowest id is applied first.

Azure App Service VNET integration and network optimization

An Azure support engineer suggested that I put two app services on the same VNET in order to optimize my traffic. I'm new to VNETs so I'm trying to grok how this works. So far I've successfully added both the app services to the same VNET. However, it's unclear to me if it's "working" or not. I've tried reading the docs but they are incredibly dense and difficult for me to see the forest for the trees. So here's where I'm at:
Based on what I've read it seems like if services are in the same VNET the traffic between them will be routed differently. For example, say I have two services: service1.mydomain.com and service2.mydomain.com. Service 1 makes calls to service 2 via the service2.mydomain.com url. Normally, that traffic would go all the way back out to the internet and back in. But it sounds like just by adding them to the same VNET the traffic is somehow routed differently on an optimized and cheaper path. Is that accurate or is there more configuration required? If so, how can I verify that it's working?
Thanks!
It depends on the App Service Plan you're using for your App Service. If you're using Azure App Services on an App Service Environment, you'll have your own VNet for routing and it should work like that (I'm not too familiar with ASEs)
However, if you're using a Premium or lower tier, VNet integration is only useful for outbound calls, meaning that an App Service will be able to access resources on that VNet, but other integrated App Services are not on that VNet, they are just able to access resources on it as well (https://learn.microsoft.com/en-us/azure/app-service/web-sites-integrate-with-vnet).
If you want the App Services to be accessed through that VNet you'll need to set up Service Endpoints or Private Endpoints. See https://learn.microsoft.com/en-us/azure/app-service/networking-features for more details
Support is correct. Since both these services are on the same VNET, traffic will not flow outside the VNET and will be optimized. This is because the default routes for all VNETs have a route with a next hop of Virtual Network.
Virtual network: Routes traffic between address ranges within the address space of a virtual network. Azure creates a route with an address prefix that corresponds to each address range defined within the address space of a virtual network. If the virtual network address space has multiple address ranges defined, Azure creates an individual route for each address range. Azure automatically routes traffic between subnets using the routes created for each address range. You don't need to define gateways for Azure to route traffic between subnets. Though a virtual network contains subnets, and each subnet has a defined address range, Azure does not create default routes for subnet address ranges, because each subnet address range is within an address range of the address space of a virtual network.
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview

Two VMs connected through VNet-to-VNet not pinging each other

Again, I tried to create a VNet-to-VNet connection.
Briefly, I created
Gateway Subnet at East US Region
Gateway Subnet at West US Region
Virtual Network Gateway for East US Region and
Virtual Network Gateway for West US Region
Using Connection type VNet-to-VNet, I connected both Virtual Network Gateway from both sides.
I created connection between both Virtual Network Gateway.
The status of both connections says, Connected.
Windows Server Domain Controller is set up at East US and Windows 10 is installed at West US.
Windows 10 is unable to ping and join the Windows Server Domain Controller.
While joining the Domain Controller, the error message is
The issue is
I am able to connect both VMs which is at two different VNets using RDP with Public IP.
Both VMs’ virtual network gateways are also connected to each other through Connections.
I am able to connect one VM from another using RDP with Private IP.
But I am not able to join Windows 10 VM to Windows Server 2016 Domain Controller.
I request please go through the link https://1drv.ms/u/s!Ail_S1qZOKPmlgBU5fLviInoisrx?e=ImrqpL and help me to fix the issue related to VNet-to-Vnet Connection so that Windows 10 VM from one VNet can join the Windows Server 2016 Domain Controller VM which is at another VNet.
I hope you'll consider it positively.
Regards
TekQ
You might have to create routes, you are not using recommended private address space so routes are not created for you.
Azure automatically creates default routes
for the following address prefixes: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16: Reserved for private use in RFC 1918.
100.64.0.0/10: Reserved in RFC 6598.
Check the effective routes to seen next hop for traffic in the peering address space.
https://learn.microsoft.com/en-us/azure/virtual-network/diagnose-network-routing-problem
Additional Information on VNet Routing
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-udr-overview
Instead of rely on Vnet Gateway and VPN S2S, you could as well using Vnet Peering between region.
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-peering-overview
I agree with the other answers. Global VNet Peering would remove the necessity of using a VPN GW, which greatly simplifies the environment and removes the monthly cost of hosting a pair of GWs. Assuming you need those GWs for other connections to VPN devices on-premises, then you can still use this design.
As Hannel pointed out, you're using public ranges for your private networks. That is also okay, but routing would be affected for VMs in those subnets if they attempted to go to actual public IPs in those ranges. Note that Hewlett Packard owns large parts of those ranges, so if your VM needed to get info from an HP website, you would have to create manual UDRs to route that traffic to Next Hop Internet.
So, please do check your Effective Routes on your NICs. You can check this from the NIC and also from Network Watcher. This should help you identify if another route is taking precedence or even if you have a route sending traffic to a virtual appliance.
Do make sure that you chose VNet-to-VNet when you set up your connection. If you chose IPSec, then you would need to have correctly configured your local network gateways.

Does Azure vnet peering support traffic passing through multiple virtual appliances that reside in the Hub vnet?

Hub and Spoke vnet peering with two virtual appliances in the Hub vnet
As shown in the above linked diagram, when the client (vnet A) needs to ping server (vnet C), is it possible to force that traffic to go through the two appliances inside the Hub vnet (vnet B)?
UDR1 forces traffic to go through Virtual Appliance Router 1, and UDR2 forces traffic out from Router 1 to Router 2, once traffic comes out of Router 2, it will arrive at server, this is done via peering itself.
UDR3 and UDR4 are for return traffic.
tcpdump on Router 1 shows traffic coming in, and then Router 1 forwards that traffic out to Router 2, but there is no traffic seen on Router 2, despite UDR 2.
However, pinging from client to server does work, this means Azure is doing the delivery, which causes the traffic to bypass Router 2.
Is multiple virtual appliances supported in a peered vnet environment? It is supported when all traffic is within the same vnet, this is tested working.
This is supported. VNet peering doesn't impose any additional restrictions. I'd recommend using Network Watcher connectivity troubleshoot to check what the issue is: https://learn.microsoft.com/en-us/azure/network-watcher/network-watcher-connectivity-portal
Are you using the two appliances as proxy? Is there a reason both ingress and egress traffic needs to go through the two appliances? Do you have a load balancer in play?

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