# Host Files/IP Address Hardcoding/DNS Caching

Source: https://developer.avalara.com/products/ecm/integration-guides/document-management/eqa6770822143770/

Guide: Exemption Certificate Management (ECM)

# Host Files/IP Address Hardcoding/DNS Caching

Resolve issues with AvaTax connectivity caused by hardcoded IP addresses, host fileentries, or DNS caching.

## What you might see or experience

-   Your AvaTax connection fails or stops working unexpectedly.
-   API requests don’t reach Avalara servers.
-   Connectivity works intermittently or only after DNS changes.

## Why this happened

AvaTax doesn’t support hardcoded IP addresses or custom host file entries. If DNS namesaren’t resolved dynamically, your system may not detect Avalara’s updated IPs.This can cause connection failures.

## What might help

Steps

Try the following:

-   Make sure that your system resolves AvaTax DNS names dynamically.
-   Remove any hardcoded IP addresses or host file entries related toAvaTax.
-   Verify that your DNS server respects DNS time-to-live (TTL) values.Avalara publishes TTL settings to allow its operations team toadjust connectivity as needed.