Azure – Networking – Part 20 – Azure Route Table

Hello Everybody,

Today I am starting with a very important azure networking concept Azure Route Table .In our last article we have covered Azure Traffic Manager. In this article we have tried to summarized the basics of Azure Route Table. Most of the information collected from different Microsoft forum/articles. There are many such article and video available but I just wanted to include this important part into my Azure Networking series. So let’s start :).

If you have missed our previous articles on azure networking, please check it in following links.

Part 1 – Basics of Azure Networking

  • *
  • *
  • *

Part 12 – Azure VPN Network Gateway

Part 13 – Configure Azure Point-to-Site VPN

Part 14 – Configure Azure VNet-to-VNet Connection

Part 15 – Configure Azure Site-to-Site VPN Connection

Part 16 – Azure Virtual Network (VNet) peering

Part 17 – VNet Peering 2 – Hub-spoke VNet topology

Part 18 – Azure Traffic Manager 1

Part 19 – Azure Traffic Manager 2 -Create Traffic Manager Profile using (Cloud Shell)

Next Article : Azure – Networking – Part 21 – Azure Route Table 2 – Configure User Define Route (UDR)

Let’s start with our today’s journey. It would be mostly on the concept with a small workshop/demo. Most of the part of this article comes from multiple Microsoft documents as well as from different sources (blogs,videos). I have tried to summarized the basics, what I learned from different sources. So that some one can found many information from one article.

Route Table In Azure Networking :

The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. Route table contains a set of Routes. Routes specifies how packets should be routed in a virtual network.

If multiple routes contain the same address prefix, Azure selects the route type, based on the following priority:

  1. User-defined route
  2. BGP route
  3. System route

Types Of Routes :

System Routes : Azure automatically creates system routes and assigns the routes to each subnet in a virtual network .Those Default/ System Routes allow traffic between virtual machines in a virtual network. Following figure showing the default/system routes provide by Azure.

Figure 1 – Azure Networking – Default System Route

In the above figure, we can see following two major information.

Address Prefixes : It holds the destination IP ranges. Azure selects a route based on the destination IP address, using the longest prefix match algorithm .

Next Hop Type : The Next Hop Type listed in the following figure represent how Azure routes traffic destined for the address prefix listed.

Figure 2 – Azure Networking – Default System Route – Next Hop Type

Optional System Routes :

Other than those above default system routes, Azure also allowing few additional system routes to their consumers. This additional system routes are option and can be available to consumer on demand. This additional routes can be available to a subnet or to all subnet of the VNet. It provides some new routes with new Next Hop Types as shown in the following figure.

Figure 3 – Azure Networking – Default Additional System Route

Custom/User Define Routes :

As per Microsoft document, from Aug 05, 2015, User Defined Routing or UDR is a significant update to Azure’s Virtual Networks. This gives a huge cost saving opportunity to the it’s customer.

We can create custom, or user-defined, routes in Azure Route Table to override Azure’s default system routes, or to add additional routes to a subnet’s route table. Following table shows the limitation on route table.

User-defined route tables200
User-defined routes per route table400

we cannot specify VNet peering or VirtualNetworkServiceEndpoint as the Next Hop Type in user-defined routes. Routes with the VNet peering or VirtualNetworkServiceEndpoint next hop types are only created by Azure, when you configure a virtual network peering, or a service endpoint.

Relation Of Subnet With Route Table And How Does It Works :

  • Route tables are associated to subnets.
  • One route table can be associated to multiple subnets.
  • One subnet can only be associated to a single route table.
  • Every subnet in a virtual network is associated with a set of built-in system routes.
  • Each packet leaving a subnet is handled based on the associated route table.
  • Packets are matched to routes using the destination.
  • Destination can be an IP address, a virtual network gateway, a virtual appliance, or the internet.
  • The packet will be dropped, if matching route not found.
  • We can not create/delete system route but we can override it by custom route.

this allows network admins to control the routing tables between subnets within a subnet as well as between VNets thereby allowing for greater control over network traffic flow.

Cost :

There are no additional charges for creating route tables in Microsoft Azure.

Permissions :

To perform tasks on route tables and routes, our account must be assigned to the network contributor role or to a custom role that is assigned the appropriate actions as shown in the following figure.

Figure 2 – Azure Networking – User Define Route-Permission

Power Shell And CLI Commands To Mange Route Table And Routes :

Following are some commands for both PowerShell and CLI command prompt to manage Route Table and its Routes. We can found examples or more details for each command from Microsoft document.

Create route table – commands
Azure CLI: az network route-table create
PowerShell: New-AzRouteTable

Create a route – commands
Azure CLI: az network route-table route create
PowerShell: New-AzRouteConfig

View details of route table – commands
Azure CLI: az network route-table show
PowerShell: Get-AzRouteTable

Dissociate a route table – commands
Azure CLI: az network route-table create
PowerShell: New-AzRouteTable

Create route table – commands
Azure CLI: az network vnet subnet update
PowerShell: Set-AzVirtualNetworkSubnetConfig

Associate a route table – commands
Azure CLI: az network vnet subnet update
PowerShell: Set-AzVirtualNetworkSubnetConfig

Delete a route table – commands
Azure CLI: az network route-table delete
PowerShell: Remove-AzRouteTable

Create a route – commands
Azure CLI: az network route-table route create
PowerShell: New-AzRouteConfig

View routes – commands
Azure CLI: az network route-table route list
PowerShell: Get-AzRouteConfig

View details of a route – commands
Azure CLI: az network route-table route show
PowerShell: Get-AzRouteConfig

Change a route – commands
Azure CLI: az network route-table route update
PowerShell: Set-AzRouteConfig

Delete a route – commands
Azure CLI: az network route-table route delete
PowerShell: Remove-AzRouteConfig

Validate routing between two endpoints – commands
Azure CLI: az network watcher show-next-hop
PowerShell: Get-AzNetworkWatcherNextHop

In my next article Azure – Networking – Part 21 – Azure Route Table 2 – Configure User Define Route (UDR) we will go through a lab test 🙂

Keep reading, share your thoughts, experiences. Feel free to contact us to discuss more.

If you have any suggestion / feedback / doubt, you are most welcome. Stay tuned on Knowledge-Junction, will come up with more such articles.

Thanks for reading 🙂 .

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