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I'm trying to configure a Cisco 886VA router to use a full-duplex fiber cable modem for internet access. The modem (Alcatel-Lucent) is pre-programmed and doesn't support DHCP (192.168.1.0/24, gateway 192.168.1.1).

The modem is connected to FastEthernet0/0 while the internal LAN is configured at FastEthernet0/1.

Could someone help me out with the necessary configuration steps, please?

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From what I understand, the modem has the internal IP is 192.168.1.1 .. If that is correct, then this is pretty simple on the router ..

from the CLI, apply the following and it should work with you ...

conf t
  int FastEthernet0/0
    ip address 192.168.1.2 255.255.255.0
    speed 100
    duplex full
    exit
  ip route 0.0.0.0 0.0.0.0 192.168.1.1

Let me explain the commands ...

conf t

This allows you to access the route configuration mode.

int FastEthernet0/0

This enters the interface configuration mode, in this case the interface is FastEthernet0/0

ip address 192.168.1.2 255.255.255.0

This adds a static IP Address of 192.168.1.2 to the interface FastEthernet0/0 to be in the same subnet of the modem (192.168.1.0/24)

speed 100

This enabled the interface to use the speed 100 MB

duplex full

This enables the interface to use full duplex

ip route 0.0.0.0 0.0.0.0 192.168.1.1

This adds a default route which informs the router to send all traffic that is not found in the routing table to the modem 192.168.1.1

But this scenario won't work, because the 192.168.1.0/24 is a private range and doesn't propagate over the internet .. The best thing is to change the modem mode to bridge this allows the router to have an IP in the same subnet of the ISP which allows you to have internet access ...

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    Please don't advise people to hard code speed and duplex unless you know their cpe requires it
    – Mike Pennington
    Commented Aug 30, 2014 at 17:16
  • Hi Mike, he actually stated in the question that he want to configure his router to use full-duplex
    – sikas
    Commented Aug 30, 2014 at 19:49
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    No he said he had a full-duplex modem; in most circumstances that doesn't require you to hard-code anything. Fast Ethernet and above autonegotiates to the highest speed and best possible duplex; even consumer electronics have done so reliably for at least a decade. Some history if you're interested
    – Mike Pennington
    Commented Aug 30, 2014 at 19:55

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