Local Network gateway BGP

Question

Local Network gateway BGP

Handian Sudianto 5,776

Hello,

I have topology like below where i set VGW as active active for redudancy.

With this topology should i define the LAN address 10.107.0.0/16 and 10.210.0.107 in LNG1 and 10.107.0.0/16 and 10.210.0.207 in LNG2? Or we let the address space to be blank?

Also in the on-premises firewall i advertise network 10.107.0.0/16, will prefix 10.107.0.0/16 which received by 10.201.0.4 will be advertise to 10.201.0.5 and 10.201.0.5 will advertise again to 10.210.0.207? So i will receive prefix 10.107.0.0/16 on my peer 10.210.0.27

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Silvia Wibowo 5,441 Reputation points Microsoft Employee

2025-03-10T06:04:03.5766667+00:00
Hi @Anonymous , please clarify:

Is BGP enabled? If BGP is enabled, no address space is required for Local Network Gateway.

If you use BGP, do you use APIPA (Automatic Private IP Addressing)? If APIPA is used, you need to set APIPA BGP IP address properly for both sides (Azure and on-premises).
Handian Sudianto 5,776 Reputation points

2025-03-11T05:42:29.7633333+00:00

is there any impact if we set or unset the address space?
Silvia Wibowo 5,441 Reputation points Microsoft Employee

2025-03-11T20:48:27.68+00:00

Hi @Handian Sudianto , the address space is required if BGP is not enabled, as it will give the VPN Gateway info for the routing. If BGP is enabled, BGP will set the routing and the address space is not looked at.

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Silvia Wibowo 5,441 Reputation points Microsoft Employee

2025-03-10T06:04:03.5766667+00:00

Hi @Anonymous , please clarify:

Is BGP enabled? If BGP is enabled, no address space is required for Local Network Gateway.

If you use BGP, do you use APIPA (Automatic Private IP Addressing)? If APIPA is used, you need to set APIPA BGP IP address properly for both sides (Azure and on-premises).
Handian Sudianto 5,776 Reputation points

2025-03-11T05:42:29.7633333+00:00

is there any impact if we set or unset the address space?
Silvia Wibowo 5,441 Reputation points Microsoft Employee

2025-03-11T20:48:27.68+00:00

Hi @Handian Sudianto , the address space is required if BGP is not enabled, as it will give the VPN Gateway info for the routing. If BGP is enabled, BGP will set the routing and the address space is not looked at.

Answer 1

Hi @Anonymous

If BGP is correctly configured, Azure will learn the routes from your on-premises firewall via BGP. Leaving the address space blank keeps the configuration clean and avoids potential conflicts and in most BGP-based VPN setups, leaving the address space blank is the best practice.

Please refer this document.

If you correctly specify the on-premises networks, it won't break anything. However, it's redundant and adds unnecessary configuration but if you specify incorrect or incomplete address spaces, it could lead to confusion and troubleshooting difficulties.

Azure might prioritize the static address spaces over the dynamically learned BGP routes in some scenarios.

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

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Local Network gateway BGP

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