updated classic.

Author: AbdullahBell

articles/expressroute/expressroute-howto-routing-classic.md

@@ -5,7 +5,7 @@ services: expressroute
 author: duongau
 ms.service: expressroute
 ms.topic: how-to
-ms.date: 12/28/2023
+ms.date: 04/22/2024
 ms.author: duau
 
 ---
@@ -48,7 +48,7 @@ This section provides instructions on how to create, get, update, and delete the
 1. **Create an ExpressRoute circuit.**
 
    Follow the instructions to create an [ExpressRoute circuit](expressroute-howto-circuit-classic.md) and provisioned by the connectivity provider. If your connectivity provider offers managed Layer 3 services, you can request your connectivity provider to enable Azure private peering for you. In that case, you won't need to follow instructions listed in the next sections. However, if your connectivity provider doesn't manage routing for you, after creating your circuit, continue with the following steps.
-2. **Check the ExpressRoute circuit to make sure it is provisioned.**
+1. **Check the ExpressRoute circuit to make sure it is provisioned.**
 
    Check to see if the ExpressRoute circuit is Provisioned and also Enabled.
 
@@ -75,7 +75,7 @@ This section provides instructions on how to create, get, update, and delete the
    ServiceProviderProvisioningState : Provisioned
    Status                           : Enabled
    ```
-3. **Configure Azure private peering for the circuit.**
+1. **Configure Azure private peering for the circuit.**
 
    Make sure that you have the following items before you proceed with the next steps:
 
@@ -151,7 +151,7 @@ This section provides instructions on how to create, get, update, and delete the
 1. **Create an ExpressRoute circuit**
 
    Follow the instructions to create an [ExpressRoute circuit](expressroute-howto-circuit-classic.md) and provisioned by the connectivity provider. If your connectivity provider offers managed Layer 3 services, you can request your connectivity provider to enable Azure private peering for you. In that case, you won't need to follow instructions listed in the next sections. However, if your connectivity provider doesn't manage routing for you, after creating your circuit, continue with the following steps.
-2. **Check ExpressRoute circuit to verify that it is provisioned**
+1. **Check ExpressRoute circuit to verify that it is provisioned**
 
    Verify that the circuit shows as Provisioned and Enabled. 
 
@@ -178,18 +178,23 @@ This section provides instructions on how to create, get, update, and delete the
    ServiceProviderProvisioningState : Provisioned
    Status                           : Enabled
    ```
-3. **Configure Microsoft peering for the circuit**
-   
-    Make sure that you have the following information before you proceed.
+1. **Configure Microsoft peering for the circuit**
+
+    Configure Microsoft peering for the circuit. Make sure that you have the following information before you continue.
 
-   * A /30 subnet for the primary link. The subnet must be a valid public IPv4 prefix owned by you and registered in an RIR / IRR.
-   * A /30 subnet for the secondary link. The subnet must be a valid public IPv4 prefix owned by you and registered in an RIR / IRR.
-   * A valid VLAN ID to establish this peering on. Verify that no other peering in the circuit uses the same VLAN ID.
+      * A pair of subnets owned by you and registered in an RIR/IRR. One subnet is used for the primary link, while the other will be used for the secondary link. From each of these subnets, you assign the first usable IP address to your router as Microsoft uses the second usable IP for its router. You have three options for this pair of subnets:
+       * IPv4: Two /30 subnets. These must be valid public IPv4 prefixes.
+       * IPv6: Two /126 subnets. These must be valid public IPv6 prefixes.
+       * Both: Two /30 subnets and two /126 subnets.
+   * Microsoft peering enables you to communicate with the public IP addresses on Microsoft network. So, your traffic endpoints on your on-premises network should be public too. This is often done using SNAT. 
+   > [!NOTE]
+   > When using SNAT, we advise against a public IP address from the range assigned to primary or secondary link. Instead, you should use a different range of public IP addresses that has been assigned to you and registered in a Regional Internet Registry (RIR) or Internet Routing Registry (IRR). Depending on your call volume, this range can be as small as a single IP address (represented as '/32' for IPv4 or '/128' for IPv6).
+   * A valid VLAN ID to establish this peering on. Ensure that no other peering in the circuit uses the same VLAN ID. For both Primary and Secondary links you must use the same VLAN ID.
    * AS number for peering. You can use both 2-byte and 4-byte AS numbers.
-   * Advertised prefixes: You must provide a list of all prefixes you plan to advertise over the BGP session. Only public IP address prefixes are accepted. You can send a comma-separated list if you plan to send a set of prefixes. These prefixes must be registered to you in an RIR / IRR.
-   * Customer ASN: If you're advertising prefixes that aren't registered to the peering AS number, you can specify the AS number to which they're registered. **Optional**.
+   * Advertised prefixes: You provide a list of all prefixes you plan to advertise over the BGP session. Only public IP address prefixes are accepted. If you plan to send a set of prefixes, you can send a comma-separated list. These prefixes must be registered to you in an RIR / IRR.
+   * **Optional -** Customer ASN: If you're advertising prefixes not registered to the peering AS number, you can specify the AS number to which they're registered with.
    * Routing Registry Name: You can specify the RIR / IRR against which the AS number and prefixes are registered.
-   * An MD5 hash, if you choose to use one. **Optional.**
+   * **Optional -** An MD5 hash if you choose to use one.
 
    Run the following cmdlet to configure Microsoft peering for your circuit: