Help Center/ Elastic Load Balance/ FAQs/ Load Balancers/ Why Are Multiple IP Addresses Required When I Create a Dedicated Load Balancer?
Updated on 2025-09-25 GMT+08:00
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Why Are Multiple IP Addresses Required When I Create a Dedicated Load Balancer?

IP addresses in the frontend subnet will be assigned to dedicated load balancers to communicate with resources over the private network. IP addresses in backend subnets are assigned to forward requests to and perform health checks on backend servers.

Table 1 shows where subnet IP addresses are used and how many IP addresses are required in each AZ. You can plan a dedicated backend subnet for a load balancer to ensure enough IP addresses for service expansion even when load balancers are using too many IP addresses.

If you are using IPv4/IPv6 dual stack, you need twice as many IP addresses in a subnet compared to using only IPv4.

Table 1 Required IP addresses in an AZ

Use Case

Subnet

AZ-Dependent or Not

Required IP Addresses in Each AZ

Virtual IP address of the load balancer

Frontend subnet

No

1

Forwarding Layer 4 requests

Backend subnet

Increases linearly with the number of AZs.
  • IP as a Backend not enabled: 0
  • IP as a Backend enabled: 4

Layer 4 health checks

Backend subnet

Increases linearly with the number of AZs.

1

Forwarding Layer 7 requests

Backend subnet

No

20

NOTE:

Load balancers sharing the same backend subnet can reuse the IP addresses in the subnet.

Layer 7 health checks

Backend subnet

No

IP addresses that are used to forward Layer 7 requests are reused.

If you create a load balancer in multiple AZs, more IP addresses will be required. There is an algorithm to determine how many IP addresses are required.

Parent topic: Load Balancers