Indicator Definitions
222 PATROL DashBoard User Guide
DNS Response Time
Drops
Reported for peers on Cisco routers (with SAA), or PETEs
Description time for a Cisco router that has SAA or a PETE peer connected to a DNS server to
return a response
The router must implement the RTTMON MIB (SAA agent). This indicator reflects
the response time that is seen by the user of the peer that is connected to the DNS
server.
Units milliseconds
Default
thresholds
minimum 500 ms–maximum 1,000 ms (1 second)
Points to check overloaded link, intermediate device, or DNS server
Reported for any device and its interfaces
Description To be processed, the packets received on the interfaces of a router-type network
device must be stored in the buffers of the internal memory. The transfer of a
packet from the interface’s memory to the device’s memory can fail. If failure
occurs, the packet is dropped. The number of drops is due to either insufficient
buffer memory or an overload of the device’s waiting queue.
For LAN switch devices, the indicator is interpreted slightly differently. The
percentage of drops corresponds more closely to the proportion of network traffic
that is seen by an interface of the LAN switch but that is not switched. For instance,
if a hub is connected to a switch, the rate of packets dropped represents the
percentage of traffic inside the group of stations on the hub. If it exceeds 50%, then
the LAN switch is underused for the concerned port and a reorganization of the
stations is needed.
Units percentage of the traffic
Default
thresholds
minimum 20%–maximum 40%
Points to check device’s memory configuration: buffers of different sizes may not be adequately
distributed for the type of network traffic or the packet waiting queue may not be
long enough
