DAG2000 Series FXS Voice Gateway User Manual
51
Dinstar Technologies Co., Ltd.
Figure 4.11-6 Ping Parameter Interface
4.11.7 Tracert Test
Tracert is trace router and used to tracking routing.
Tracert sends a sequence of Internet Control Message Protocol (ICMP) echo request packets
addressed to a destination host. Determining the intermediate routers traversed involves
adjusting the time-to-live (TTL), aka hop limit, Internet Protocol parameter. Frequently starting
with a value like 128 (Windows) or 64 (Linux), routers decrement this and discard a packet
when the TTL value has reached zero, returning the ICMP error message ICMP Time Exceeded.
Tracert works by increasing the TTL value of each successive set of packets sent. The first set of
packets sent have a hop limit value of 1, expecting that they are not forwarded by the first
router. The next set have a hop limit value of 2, so that the second router will send the error
reply. This continues until the destination host receives the packets and returns an ICMP Echo
Reply message.
Trace route uses the returned ICMP messages to produce a list of hops (which usually consists
of routers and layer 3 switches) that the packets have traversed. The timestamp values
returned for each router along the path are the delay (aka latency) values, typically measured
in milliseconds for each packet.
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