Panasonic Panafax DX-2000, Руководство по обслуживанию

Страница: 175 / 322

175
4. Tracing a Packet Route
Another useful command-line utility is TRACERT, which is used to verify the route a packet takes to reach its destination. The
result shows each router crossed and how long it took to get through each particular router to reach the specified destination.
The time it takes to get through a particular router is calculated three times and displayed for each router hop along with the IP
Address of each router crossed. If a FQDN (Fully Qualified Domain Name) is available, it will be displayed as well.
This utility is useful for two diagnostic purposes:
a. To detect whether a particular router is malfunctioning along a known path. For example, if you know that packets on a
network always go through London to get from New York to Berlin, but the communication is failing. A TRACERT to the
Berlin address shows all the hops up to the point where the router in London should respond. If it does not respond, the
time values are shown with an asterisk (*), indicating the packet timed out.
b. To determine whether a router is slow and needs to be upgraded or additional routers should be installed on the network.
You can determine this by simply comparing the time it takes for a packet to get through a particular router. If its return
time is significantly higher than the other routers, it should be upgraded.
To use this utility, from the DOS command-line, type: tracert <IP Address or Hostname>
Tracing the Route to SMTP/POP Server
5. Managing Network Route Tables
In the simplest case a router connects two network segments (see System Diagram Model on page 153).
In this model, the system used to join the two segments needs to know only about these segments.
The routing table for router R1 in this case is simple; the following table shows its key routes:
When the DX-2000 at 192.168.3.5 attempts to communicate with the DX-2000 at 192.168.1.x, IP performs the AND’ing pro-
cess to find two things: The local network ID is 192.168.3.0, and the destination network ID is not. This means, that the des-
tination host is not on the local network.
IP, is responsible to find a route to the remote network, and therefore, it consults the routing table. Here, the local host nor-
mally determines that the next step in the route is the Default Gateway, and sends the packet to router R1.
The router R1, receives the packet. After determining that the packet is for another host and not the router itself, it checks the
routing table. It finds the route to 192.168.1.0 and sends the packet through the interface to the DX-2000 at 192.168.1.x,
which receives the packet. This is a simple route that took only a single hop.
When another network is added as the number of hosts grows, it gets complicated, and the systems on the most distant net-
works cannot communicate. When the router receives a packet in this case, it cannot find a route to the remote network It
then discards the packet and a message indicating "destination host unreachable" is sent to the originator.
Here, is where the ROUTE command-line utility is useful when dealing with more than two networks, and is used by Adminis-
trators to statically manage a route table by adding, deleting, changing and clearing the route table. It has a number of
options that are used to manipulate the routing tables, some are shown below:
Network Address Netmask Gateway Interface
192.168.3.0 255.255.255.0 192.168.3.254 192.168.3.254
192.168.1.0 255.255.255.0 192.168.1.253 192.168.1.253
C:\WINDOWS>tracert sv2.labo.mgcs.com
Tracing route to sv2.labo.mgcs.com [192.168.1.2]
over a maximum of 30 hops:
1 4 ms 2 ms 2 ms 192.168.3.254
2 4 ms 5 ms 5 ms sv2.labo.mgcs.com [192.168.1.2]
Trace complete.