Connection Issues with Android WebView and Custom DNS (AdGuard DNS) on Vercel-Hosted Subdomains

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1

Hello Vercel Team,

I’m experiencing a CONNECTION_REFUSED error when trying to access Vercel-hosted subdomains via an Android WebView on devices using a custom DNS (specifically AdGuard DNS).

I’m currently using Namecheap DNS and have added three subdomains to Vercel, each linked to a separate branch. I configured each subdomain as a CNAME record pointing to cname.vercel-dns.com. on my Namecheap domain.

To explain in more detail:
I’m using the domain fairytech.ai with the subdomains cashback-ui.moment-dev, cashback-ui.moment-canary, and cashback-ui.moment.
In Vercel, I’ve set up these as cashback-ui.moment-dev.fairytech.ai, cashback-ui.moment-canary.fairytech.ai, and cashback-ui.moment.fairytech.ai.
On Namecheap, the fairytech.ai domain has three CNAME records for cashback-ui.moment-dev, cashback-ui.moment-canary, and cashback-ui.moment, each pointing to cname.vercel-dns.com..

Here are the screenshots from Vercel and Namecheap service.

Domain settings in Vercel

스크린샷 2024-11-06 오후 2.43.01
스크린샷 2024-11-06 오후 2.43.011964×1276 158 KB

CNAME record settings in Namecheap

스크린샷 2024-11-06 오후 2.44.38
스크린샷 2024-11-06 오후 2.44.382260×410 18.6 KB

The setup works as expected when accessing these URLs through a browser from desktop or android WebView when custom DNS is off.
However, I’m experiencing an issue when trying to access these subdomains via an Android WebView, specifically on devices using a custom DNS (e.g., dns.adguard.com),
I receive a CONNECTION_REFUSED error in the onReceivedError callback.
I expect vercel deployed site is also accessible on devices using custom DNS.

Could you please advise on how to resolve this issue? Are there additional configurations I should consider for compatibility with custom DNS services?

Thank you for your assistance!

Deployment URL or Custom Domain: detail listed above
Environment (local, preview, production): 2 subdomains are preview, 1 subdomian is production
Project Framework: React app(accessed via Android WebView)
Build Settings:
  Framework Preset:
  Build Command (if not default):
  Output Directory (if not default):
  Install Command (if not default):
Node/Runtime Version:
Package Manager:
Relevant Packages:
4

Hi, @sarahshin0716! Welcome to the Vercel Community :smile:

Thanks for being patient with us :pray:

First, let’s verify your current DNS configuration:

  1. Your Namecheap DNS settings look correct. You’ve set up CNAME records for each subdomain pointing to cname.vercel-dns.com., which is the correct configuration for Vercel-hosted domains.
  2. Your Vercel domain settings also appear to be correctly configured, with each subdomain properly added to your project.

Given that the setup works correctly when not using a custom DNS, the issue likely lies in how AdGuard DNS (or other custom DNS services) are resolving these subdomains.

In addition to the CNAME records, try adding A records for each subdomain pointing to Vercel’s IP addresses. This can sometimes help with DNS resolution issues .

Add the following A records in your Namecheap DNS settings:

76.76.21.21
76.76.21.98
76.76.21.99

You can use a tool like DNS Checker to verify that your DNS records have propagated correctly across different DNS servers.

Let us know how you get on!