Azure / , Networking / Dec. 18, 2018 / Matt Davies | Partner

Cross Region, Peering Pitfalls. .

Ah if only all pitfalls were fun. Remember Pitfall on the Atari  2600. It was the second best selling game after Pac-Man. Pitfall Harry had to negotiate a jungle full of hazardous quicksand, rolling logs, fire and rattle snakes to recover precious treasures. 

Recently we did some work with a customer where they made use of two Azure regions (Australia East and Australia Southeast) for their IaaS workloads. The eastern region was used to house their production IaaS workloads and the southeastern region was treated as a fail over region to be used in fail over / disaster recovery situations. Each region had a couple of virtual networks and virtual network peering had been configured between them. Unbeknown to us we were about to encounter a slightly less entertaining or pleasurable pitfall whilst attempting to utilise two specific properties of virtual network peering.

  • Allow Gateway Transit
  • Use Remote Gateways 

If you are not familiar with peering, virtual network peering seamlessly connects two Azure virtual networks, merging the two virtual networks into one for connectivity purposes. Virtual network peering also has an appealing feature “Gateway transit”. Gateway transit is a peering property that enables one virtual network to utilise the gateway in the peered virtual network for cross-premises or VNet-to-VNet connectivity.

You can read up on peering and the Gateway transit feature here: https://docs.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-peering-gateway-transit

This works great, however when trying to enable this between our two Azure regions we discovered that the “Allow Gateway Transit” and “Use Remote Gateways” properties are unavailable. 

When we tried to enable this we were greeted with the following error:

“Failed to save virtual network peering ‘<peeringName>’. Error: AllowGatewayTransit and UseRemoteGateways options are currently supported only when both peered virtual networks are in the same region.”

You’ll also see the following in the Azure Portal:

Whilst this isnt a bug, Microsoft actually describe this here: https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-peering-overview in our case it was still a less than desirable outcome. Fear not, if you really require transit across the gateway in your remote virtual network, we may have a possible solution for you. . 

Work around:

Establish a site to site VPN between regions and control routing via route tables and or BGP depending on your configuration. A VPN can be quickly created via ARM template, the portal or PowerShell.

If this sounds like the workaround you’ve been looking for, here is some PowerShell to get you started.


$prodSharedKey = 'mysharedkeygoeshere'
 
# AE variables
$AERG = "internal-networking-ae-rg"
$AELocation = "australiaeast"
$AEVNetName = "internal-vnet"
$AEGWName = "internal-vnet-ae-vpn-vng"
$AEGWIPName = "internal-vnet-ae-vpn-vng-pip"
$AEGWIPconfName = "gwipconfAE"
$ConnectionAEASE = "internalVNetAEtoInternalVNetASE"
 
# ASE variables
$ASERG = "internal-networking-ase-rg"
$ASELocation = "australiasoutheast"
$ASEVnetName = "internal-vnet"
$ASEGWName = "internal-vnet-ase-vpn-vng"
$ASEGWIPName = "internal-vnet-ase-vpn-vng-pip"
$ASEGWIPconfName = "gwipconfASE"
$ConnectionASEAE = "internalVNetASEtoInternalVNetAE"
 
# - Australia East Side
$AEgwpip = New-AzureRmPublicIpAddress -Name $AEGWIPName -ResourceGroupName $AERG -Location $AELocation -AllocationMethod Dynamic
 
$AEvnet = Get-AzureRmVirtualNetwork -Name $AEVNetName -ResourceGroupName $AERG
$AEsubnet = Get-AzureRmVirtualNetworkSubnetConfig -Name "GatewaySubnet" -VirtualNetwork $AEvnet
$AEgwipconf = New-AzureRmVirtualNetworkGatewayIpConfig -Name $AEGWIPconfName -Subnet $AEsubnet -PublicIpAddress $AEgwpip
 
New-AzureRmVirtualNetworkGateway -Name $AEGWName -ResourceGroupName $AERG -Location $AELocation -IpConfigurations $AEgwipconf -GatewayType Vpn -VpnType RouteBased -GatewaySku VpnGw1
 
# - Australia South East Side
$ASEgwpip = New-AzureRmPublicIpAddress -Name $ASEGWIPName -ResourceGroupName $ASERG -Location $ASELocation -AllocationMethod Dynamic
 
$ASEvnet = Get-AzureRmVirtualNetwork -Name $ASEVnetName -ResourceGroupName $ASERG
$ASEsubnet = Get-AzureRmVirtualNetworkSubnetConfig -Name "GatewaySubnet" -VirtualNetwork $ASEvnet
$ASEgwipconf = New-AzureRmVirtualNetworkGatewayIpConfig -Name $ASEGWIPconfName -Subnet $ASEsubnet -PublicIpAddress $ASEgwpip
 
New-AzureRmVirtualNetworkGateway -Name $ASEGWName -ResourceGroupName $ASERG -Location $ASELocation -IpConfigurations $ASEgwipconf -GatewayType Vpn -VpnType RouteBased -GatewaySku VpnGw1
 
# Connection
$AEvnetgw = Get-AzureRmVirtualNetworkGateway -Name $AEGWName -ResourceGroupName $AERG
$ASEvnetgw = Get-AzureRmVirtualNetworkGateway -Name $ASEGWName -ResourceGroupName $ASERG
 
New-AzureRmVirtualNetworkGatewayConnection -Name $ConnectionAEASE -ResourceGroupName $AERG -VirtualNetworkGateway1 $AEvnetgw -VirtualNetworkGateway2 $ASEvnetgw -Location $AELocation -ConnectionType Vnet2Vnet -SharedKey $prodSharedKey
New-AzureRmVirtualNetworkGatewayConnection -Name $ConnectionASEAE -ResourceGroupName $ASERG -VirtualNetworkGateway1 $ASEvnetgw -VirtualNetworkGateway2 $AEvnetgw -Location $ASELocation -ConnectionType Vnet2Vnet -SharedKey $prodSharedKey

Once you’ve solved this issue, you can play Pitfall online here: https://www.retrogames.cz/play_029-Atari2600.php?language=EN

 

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