Explore metrics in the ExtraHop system to investigate DNS failures

If a slow internet issue is reported, look at the system dashboards to determine whether the issue is related to network throughput or to the DNS protocol.

1. Log in to the ExtraHop system through https://<extrahop-hostname-or-IP-address>.
2. Click the global time selector in the top-left navigation bar, select Last 7 days, and then click Save.

   Note:

   Changing the global time interval gives you a chance to see network and protocol behavior that occurred prior to the detected problem.

3. Click Dashboards, and then click Network in the System Dashboards collection.
4. Confirm that the Network Throughput and L2 Packets charts show normal or consistent peaks, similar to the figure below. A large discrepancy between maximum rates and average rates can indicate network issues are affecting internet performance. Otherwise, continue your investigation into DNS metrics.
   
5. Click Activity in the System Dashboards collection.
6. Scroll down to the All Activity DNS Server Processing Time and All Activity DNS charts.
   1. The All Activity DNS Server Processing Time chart shows you the time between the last packet of a DNS request from a client and the first packet of a DNS response from the server. Hover over the median to compare the processing time at the same time point. A large difference between the median value and 95th percentile indicates that something might be wrong with a DNS server in your network.
      
   2. The All Activity DNS chart correlates responses and errors. A spike in errors can add delays of two to four seconds for clients, servers, applications, and customers. In the figure below, the proportion of responses to errors looks consistent.
      

The DNS metric, Request Timeouts, indicates a failure to fulfill a DNS request. DNS servers that are not fulfilling requests can negatively affect application and internet performance. Let's look at the total number of Request Timeouts for DNS servers on our network on a protocol page. The protocol page for the All Activity application provides an overview of important metrics for all the activity across your network, including DNS protocol activity. We can then drill-down to see which DNS servers are timing out.

1. On the Activity dashboard, click the All Activity DNS chart title.
2. In the Go to application... section of the drop-down menu, click All Activity DNS.
   The All Activity protocol page appears.
3. In the left pane, click DNS.
4. View the number of Request Timeouts. In the figure below, the number is high (1,174,645) and worth investigating further.
   
   
   
5. Click the metric value for Request Timeouts and then select Server, as shown in the figure below.
   
   
   
   A detail metric page appears that displays all the server IP addresses in your network with request timeouts.
6. Note which devices have the highest number of Request Timeouts. In the figure below, this is Device 192.168.35.103.
   
7. In the Host column, click the name of the device with the highest number of request timeouts.
   A new protocol page appears, which displays metrics specific to Device 192.168.35.103. Now we can examine which clients are affected by this DNS server.

You can now identify which clients sent requests to this DNS server and might be affected by DNS Request Timeouts.

1. From the protocol page for Device 192.168.35.103, click DNS in the Server Activity section in the left pane.
2. In the DRILL DOWN section near the top of the page, click Clients.
   
   
   
   A detail metric page appears that displays all the client IP addresses that sent requests to the DNS server.