How does DNS resolution affect Varnish and the 54113 error?

If Varnish is configured to use hostnames for your backend servers, it relies on DNS to resolve those hostnames to IP addresses. If DNS resolution fails or returns an incorrect IP address, Varnish won't be able to connect to the backend, resulting in a 54113 error. Verify that your DNS server is functioning correctly and that the backend hostnames resolve to the correct IP addresses. Use `nslookup` or `dig` to test DNS resolution.