Test-Um NT750 - Manual (Page 11)

LanScaper
TM
The tester sends out an ARP packet directed to the Router, and needs a response from the Router
informing the tester of the Router's MAC address. During this phase, “ARP” will flash under the
“Rtr” acronym. If no response is received to the ARP request, the tester will repeat the request at
varying intervals (1-3 seconds). No response to the ARP can mean that the IP address assigned to
the Router is not correct, the Router is non-functional, or that it is not accessible on the LAN due to
some other problem. If the Rtr conversation is selected, and the SEL button pressed, the status
displayed is “No ARP response”.
Once the Router MAC address is found, the LanScaper™ begins sending ICMP echo request
(PING) packets to the Router. The status displayed under the Rtr acronym changes to
| with the
Symbol bouncing back and forth across the net ( | ). Each time the tester sends a PING request,
the is shown on the left side of the net. Each time a response is received, the bounces to the
other side. If no shows on the right, while it is blinking on the left, it means that the tester is
sending, but the Router is not answering. Selecting the Rtr acronym and pressing SEL twice will
show the present IP address for the router on the top line and the count of the X (transmit) and R
(receive) packets. If no PING response has been received, the status is “No PING Response.”
Missing Receive packets can mean that the LAN or the Router is busy, or that there is some other
problem on the LAN. Pressing the SEL button again will drop down to the third status screen
which shows the time between the transmission of the last received PING packet and its reception
time on the top line of the LCD, and the average time between transmission and reception of all
PING packets to the router in this conversation on the bottom line.
The Target IP address can either be on the LAN segment or remote. If the Target is on the LAN, the
status of the LanScaper™ Target conversation will be as described for the Router above. In the off
local segment case, where the PING packets needs to be sent to the Router to be forwarded, there is
an additional step necessary and status displayed. When the Router is required for Target
conversation, the status shown for the Target is “---“ while the tester is attempting to contact the
Router. The detailed status for the Target is “No Rtr response.” In the case where the Target is
remote, and an ARP response has been received from the Router, the Target PING packets are sent
to the Router which is expected to forward them on to the Target. If no response is returned from
the Target, possible causes are the Target cannot be reached due to network problems, the Target is
not responsive, or that the device that is active at the IP address selected for the Router is not a
Router, and is not forwarding the packets.
The DNS conversation is only active when PING test is run in the DHCP On mode because the
DNS IP address is only available from the DHCP server. (Note that if known, the DNS server IP
address can be entered as a Target and PINGed like any other Target.) The DNS server can be local
or remote, like a Target. The DNS conversation status is similar to a Target conversation status.
In most small LAN configurations, the DNS server will be a remote device, and successful
PINGing to it will verify proper LAN operation and Internet connectivity.
The tester will shut off automatically about 15 minutes after the last button press. The user can also
terminate the test by pressing the CABLE, NTWRK or PWR buttons. In any of these cases, the
LanScaper
will issue a DHCP release request to the DHCP server when in DHCP On mode. This
is preferable to simply disconnecting the cable to terminate the test because the address assigned to
the LanScaper™ will not be available for assignment to another device.
TM