Azure ExpressRoute Cheat Sheet by ilperdan0

Where is the menu to config Expres­sRoute circuit in Azure portal?

Create a resource > Networking > Expres­sRoute.

What we do after the provider status is reported as Provis­ioned?

For Layer 2 connec­tivity, configure the routing for the peerings. For L3, the provider will configure that.

Circuit name

A meaningful name for your circuit, without any white space or special charac­ters.

Peering location

A location enabled by the Expres­sRoute provider in which to create your circuit.

SKU

Select Standard if you have up to 10 virtual networks and only need to connect to resources in the same geopol­itical region. Otherwise, select Premium.

Subscr­iption

The subscr­iption you've registered with your Expres­sRoute provider.

Location

The Azure location in which to create the circuit.

Peer ASN

The autonomous system number for your side of the peering. This ASN can be public or private, and 16 bits or 32 bits.

Secondary subnet

This is the address range of your secondary /30 subnet. This subnet provides a secondary link to Microsoft. The first two addresses are used to hold the IP address of your router and the Microsoft router.

Shared key

This is an optional MD5 hash that's used to encode messages passing over the circuit

Advertised public prefixes

This is a list of the address prefixes that you use over the BGP session. These prefixes must be registered to you, and must be prefixes for public address ranges.

Routing registry name

This name identifies the registry in which the customer ASN and public prefixes are regist­ered.

What we create before connect to a private circuit?

Must create an Azure virtual network gateway by using a subnet on one of your Azure virtual networks.

What we use to control traffic that's routed from on-pre­mises network?

Network security groups and firewall rules

How many Expres­sRoute circuit can a single virtual network can connect to?

You can link a single virtual network to four Expres­sRoute circuits if necessary.

What is Expres­sRoute Direct option?

An ultra-­hig­h-speed option from Microsoft.

What is FastPath

When FastPath is enabled, it sends network traffic directly to a virtual machine that's the intended destin­ation. The traffic bypasses the virtual network gateway, improving the perfor­mance between Azure virtual networks and on-pre­mises networks.

Where Expres­sRoute is supported?

across all regions and locations

What are circuits?

The connec­tions to an endpoint in an Expres­sRoute location that enable customer to peer on-pre­mises networks with the virtual networks available through the endpoint.

Do circuit establ­ishes via public internet?

No, A circuit is establ­ished across a private wire rather than the public internet.

Expres­sRoute network and routing requir­ements

- Ensure that BGP sessions for routing domains have been config­ured. For each Expres­sRoute circuit, Microsoft requires redundant BGP sessions between Micros­oft’s routers and customer peering routers.
- Using NAT to IP Public is mandatory to connect through Microsoft peering. Microsoft will reject anything except public IP addresses through Microsoft peering.
- Reserve several blocks of IP addresses in your network for routing traffic to the Microsoft cloud. 1 /29 or 2 /30.
- One of these subnets is used to configure the primary circuit to the Microsoft cloud, and the other implements a secondary circuit.
- Use the first address in these subnets to commun­icate with services in the Microsoft cloud. Microsoft uses the second address to establish a BGP session.

What is the constraint of Expres­sRoute private peering?

The resources that customer access must all be located in one or more Azure virtual networks with private IP addresses. Customer can't access resources through their public IP address over a private peering.