Point-to-point numbered refers to
connections where the interfaces connecting the routers
to the WAN have IP addresses. On both WAN ports, the
address of the WAN port is set to an IP address on a
common IP network, and the destination addresses are
set to the IP address of WAN port of the unit on the
far side of the link.
====ETHERNET===================== 192.168.1.0/24 ===
|
| LAN IP: 192.168.1.100
+-------+--------+
| |
| Router A |
| Serial0 |
+-------+--------+
| WAN IP: 192.168.54.1/30 (255.255.255.252)
|
[-] CSU/DSU (may be integrated on WAN card)
|
| PTP WAN
|
[-] CSU/DSU (may be integrated on WAN card)
|
| WAN IP: 192.168.54.2/30 (255.255.255.252)
+-------+--------+
| Serial0 |
| Router B |
| |
+-------+--------+
| LAN IP: 192.168.2.200
|
====ETHERNET===================== 192.168.2.0/24 ===
Before You Start
Be sure to have three separate IP
subnets, one for the WAN network and two for the Ethernets
connected to the routers. Each WAN port connected to
the point-to-point WAN must have it's own IP address
from the same IP network. Since they are on the same
IP network, they will have the same netmask.
These IP network addresses are given to you by your
Internet Service Provider, your leased line carrier,
or by ARIN. If you
do not plan to connect you network to the Internet,
you can use an IP network address set aside for private
use. The IP network address for private use can be found
in RFC 1597. Most people will use 192.168.0.0 as we
have in this example.
Configuring The WAN Ports
In this example, we are going to
assume the following:
- Router A has an Ethernet IP address
of 192.168.1.100 with a netmask of 255.255.255.0
- Router A has a WAN IP address of
192.168.54.1 with a netmask of 255.255.255.252
- Router B has an Ethernet IP address
of 192.168.2.200 with a netmask of 255.255.255.0
- Router B has a WAN IP address of
192.168.54.2 with a netmask of 255.255.255.252
- Router A is providing Internet access
to Router B.
- The WAN port on both routers is Serial0.
The IP addresses used in this Technical
Note are examples only, you will need to use an IP network
given to you by your Internet Service Provider.
Router A
!
version 2.00
!
interface Ethernet0
ip address 192.168.1.100 255.255.255.0
!
interface Serial0
description Connection to Router B
encapsulation hdlc
ip address 192.168.54.1 255.255.255.252
!
ip route 0.0.0.0 0.0.0.0 192.168.1.1
!
end
Router B
!
version 2.00
!
interface Ethernet0
ip address 192.168.2.200 255.255.255.0
!
interface Serial0
description Connection to Router A
encapsulation hdlc
ip address 192.168.54.2 255.255.255.252
!
ip route 0.0.0.0 0.0.0.0 Serial0
#Alternate default route command
#ip route 0.0.0.0 0.0.0.0 192.168.54.1
!
end
Troubleshooting
If the port does not have an "up"
status for both hardware and protocol in the interface
statistics output (Option 2 from the Main menu) do the
following:
If hardware shows "down", check your cable connections
and ensure that you have connected to the correct port.
If you have connected to the correct port, double-check
the telephone company smart jack or other telephone
company-installed equipment for your circuit. The smart
jack should show no red alarms if the cables are connected.
If, after connecting the cables correctly, you have
errors on the telephone company equipment, contact your
line provider for assistance.
If hardware shows "up", but protocol shows "down", you
should see the PPP negotiation and see the status of
the WAN port change to up. At this point you should
be able to ping the other side.
If you have an external CSU/DSU, put the CSU/DSU into
a local loopback. This will cause each packet sent to
the CSU/DSU to reflect back to the WAN port. This is
for testing only, the line will not function while the
CSU/DSU is in a local loopback. If, in the interface
statistics detail output for the port, you see transmitted
packets immediately received on the same port, then
you can determine the following facts:
- The WAN port on the router is sending
and receiving data.
- The cable and connectors between
the router and the CSU/DSU are functioning.
- The DTE port on the CSU/DSU is functioning.
- THE ROUTER IS FUNCTIONING AS IT SHOULD.
If you don't get your packets back
immediately on the same interface:
- For cards with a software-selectable
serial interface, check that you have specified
the correct wiring specification (V.35, RS232, RS422/X.21).
The "dctype" command is typically set to V.35 (the
default) in North America and RS422 in Europe and
Asia.
- That all cables are securely connected.
- Begin swapping hardware, cables,
CSU/DSU, etc.
If you get your packets back immediately,
but the line protocol status is not "up":
- Check the CSU/DSU settings such as
clocking, etc. Almost always the CSU/DSU should
be set for external clocking. Your line provider
typically provides the clock. It's not a bad idea
to verify any external CSU/DSU settings with the
manufacturer.
- Have their telephone carrier test
the line. Requesting a hard copy of the test results
will often get you a better test.
If the line protocol status is "up"
but you can't ping the other side:
- Double check settings. Make sure
that the IP address for the WAN port on both sides
are in the same subnet.
- Do a traceroute from your workstation
through the local (to you) router to the router
in trouble. Then do a traceroute from the router
in trouble (assuming you can get to it) back to
your workstation. The problem will lie in the gap
between the two traceroutes.
- Make sure the default gateway is
set to the upstream router or the serial device
used for the upstream connection, as in our example
above on Router B.
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