DNS Resolution

This page is meant to help with DNS issues such as determining if DNS is being handled properly.

Caching and Time To Live (TTL)

DNS records are cached. How often records that have been cached are updated depends on their Time To Live (TTL) values.

$ nslookup  -debug example.com ns1.dreamhost.com
Server:  ns1.dreamhost.com
Address:  66.33.206.206#53

------------
Got answer:
    HEADER:
        opcode = QUERY, id = 17, rcode = NOERROR
        header flags:  response, auth. answer, want recursion
        questions = 1,  answers = 1,  authority records = 0,  additional = 0

    QUESTIONS:
        example.com, type = A, class = IN
    ANSWERS:
    ->  example.com
        internet address = 208.113.209.221
        ttl = 14400 (4 hours)

------------
Name:    example.com
Address:  208.113.209.221

This is an example of a domain hosted with DreamHost. The TTL is set to 4 hours. If an ISP honors this TTL value then if the IP address above changed one should expect the ISP to return the new address in 4 hours or less.

When the nameservers are changed for a domain it may take much longer for an ISP to resolve to the new IP address because the TTL may be set to 2 days. This is why you may hear it takes two days to "propagate."

---

Troubleshooting

The instructions provided in this article or section are considered advanced. You are expected to be knowledgeable in the UNIX shell. Support for these instructions is not available from DreamHost tech support. Server changes may cause this to break. Be prepared to troubleshoot this yourself if this happens. We seriously aren't kidding about this.

For domains and subdomains hosted at DreamHost, the records should appear in the "DNS" panel when using the Domains -> Manage Domains section of the DreamHost Web Panel.

Next they should be returned when querying the DreamHost nameservers directly.

$ nslookup -debug -norecurse -query=A example.com ns1.dreamhost.com
Server:         ns1.dreamhost.com
Address:        66.33.206.206#53

------------
    QUESTIONS:
        example.com, type = A, class = IN
    ANSWERS:
    ->  example.com
        internet address = 208.113.209.221
    AUTHORITY RECORDS:
    ADDITIONAL RECORDS:
------------
Name:   example.com
Address: 208.113.209.221

DNS is configured correctly given that the "A" record in our "DNS" panel shows the same IP address.

Now here is an example of a domain not hosted at DreamHost:

Server:         ns1.dreamhost.com
Address:        66.33.206.206#53

------------
    QUESTIONS:
        example.com, type = A, class = IN
    ANSWERS:
    AUTHORITY RECORDS:
    ADDITIONAL RECORDS:
------------
** server can't find example.com: SERVFAIL

So at this point if you had used Domans -> Manage Domains to add the domain and waited a while you should try to refresh the DNS information using the "DNS" panel. If that doesn't work contact Support.

Now so far we've queried DreamHost directly. But your local computer may be configured to use a local computer for DNS resolution. In addition an ISP will provide IP addresses for your computer to connect to for DNS resolution. DreamHost support won't be able to help if a DNS problem lies with either one, or any DNS servers between DreamHost and the one you use for DNS resolution.