Any ideas on how to assign Azure public ip and subnet mast to cisco asav

Question

I have been asked to setup and Cisco asav on azure, so I can assign the public interface on the cisco firewall but it does not like /32 for a single public ip. Anyone know what subnet to configure on my external inferface so it keeps the firewall happy. Thanks

Answer 1

Hi @Garth Taylor, there are 2 sets of routing:

• Azure Virtual Network routing -> this is applied as Route Table on the subnets. Once you've created vnet peering, there will by system-injected routes that complement the Route Table to inform about routes to the other vnet. Since you've created vnet peering, I think your setup is already good for this.
• Routing in Cisco ASAv -> you need to set default route to Outside interface.

Answer 2

Hello @Garth Taylor ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you would like to know how to assign an Azure public IP and subnet to cisco asav firewall during its deployment.

You can find more information about the Prerequisites and deployment options for the Cisco ASAv in the below docs:

https://www.cisco.com/c/en/us/td/docs/security/asa/asa98/asav/quick-start-book/asav-98-qsg/asav-azure.html

https://www.cisco.com/c/en/us/td/docs/security/asa/asa98/asav/quick-start-book/asav-98-qsg/asav-azure.html#id_48477

You can also refer this blog for detailed instructions with screenshots:

Anyone knows what subnet to configure on my external interface, so it keeps the firewall happy.

The smallest supported IPv4 subnet in Azure is /29, and the largest is /2 (using CIDR subnet definitions).

Refer: https://learn.microsoft.com/en-us/azure/virtual-network/virtual-networks-faq#how-small-and-how-large-can-virtual-networks-and-subnets-be

So, you need to make sure that the subnet you define is either /29 or larger such as /28, /27 and so on.

Kindly let us know if the above helps or you need further assistance on this issue.

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