Windows – how to clear Window DNS cache

The DNS cache doesn't ever flush, unless you explicitly tell it to or you make a DNS/networking related configuration change. DNS records have a Time To Live (TTL) value associated with them which tells a DNS cache how long the particular record is good for. Records in the cache are kept for their TTL, then re-queried.

On a Windows machine you can see a list of all the records in your cache along with their TTL by executing the following command at the command prompt:

ipconfig /displaydns

You can force a flush of all cached DNS records using the following command:

ipconfig /flushdns

For more info:

• Wikipedia article on DNS and TTLs

Pings from the internet are generally disabled by ISPs. Pings are ICMP messages, and therefore treated differently than regular traffic. The other possibility is that the pings are being blocked by your router, why not log into your router and look for a setting that says something about responding to pings/icmp packets.

There are several ports that Comcast blocks, as of last month they block 25, 68, 135-139, 445, 520, and 1080.

Let the Trace Route run until it is done, some routers won't respond which appears as a timeout, but the trace route is still running, and routers at the end may still respond.