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Configure router for internet access

Brian Taylor
Level 1
Level 1


I'm trying to find information on configuring a 877 to allow internet access on one of the Ethernet ports (e.g. fas2).

Currently internet is supplied via an external Ethernet device which returns the following information when plugged into a laptop:

   Description . . . . . . . . . . . : Realtek PCIe GBE Family Controller
   Physical Address. . . . . . . . . : D8-9D-67-CA-62-15
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::5438:6d7e:1491:ad3a%19(Preferred)
   IPv4 Address. . . . . . . . . . . :
   Subnet Mask . . . . . . . . . . . :
   Lease Obtained. . . . . . . . . . : Saturday, 13 February 2016 1:12:22 PM
   Lease Expires . . . . . . . . . . : Tuesday, 16 February 2016 1:12:20 PM
   Default Gateway . . . . . . . . . :
   DHCP Server . . . . . . . . . . . :
   DHCPv6 IAID . . . . . . . . . . . : 366517607
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-19-39-5C-BB-B8-76-3F-53-F7-67
   DNS Servers . . . . . . . . . . . :
   NetBIOS over Tcpip. . . . . . . . : Enabled

How can I configure a port for internet traffic and route all traffic externally through a Fast Ethernet port - are there instructions for this?


15 Replies 15

Level 1
Level 1

Seems like the ISP is using a modem/router combo box which is why you're being supplied an internal IP address. You could call your ISP and tell them you want to use your own router and they need to put their modem in bridge mode. As for the router it's a pretty simple setup and you will need command line access via console cable or telnet/ssh. 

Here's an example config that you can alter to fit your needs:

ip dhcp pool Internal
   import all



ip access-list standard NAT


ip nat inside source list NAT interface FastEthernet0/0 overload


interface FastEthernet0/0

ip address dhcp

ip nat outside

no shut


interface FastEthernet0/1

ip address

ip nat inside

no shut


Thank you very much for your reply. I can contact the ISP regarding the bridge and I'm looking through your example now. By the way I get the below message when selecting the interface mentioned in your post - what does it mean? The arrow is pointing to the "/" character.

dslmodem(config)#interface FastEthernet0/0
% Invalid input detected at '^' marker.


I ended up with the following. Still need to check with the ISP on the bridging.

interface FastEthernet2
 switchport trunk native vlan 3
 switchport mode trunk

interface Vlan3
 ip address dhcp
 ip access-group 101 in
 ip nat outside
 ip virtual-reassembly

ip nat inside source list 3 interface Vlan3 overload

Hi sir brian,
Did Mionan's commands work? Because I wanna use them as well.

Level 1
Level 1

I am sharing a great content which will demonstrate step by step process of Connecting Cisco 2851 Router and Cisco 3560 Switch to ISP Home router and Configuring Cisco Router using Putty and finally Accessing Internet from Laptop and Desktop PC through this network. 


PuTTY command line for Router Configuration:

Where hostname of the Router is "Router"

Entering to Privileged mode:


Check IP Interface:

Router#show ip interface brief

Entering to Global Configuration mode:

Router#configure terminal

Entering GE0/0 Interface:

Router(config)#interface gigabitEthernet 0/0

Making Interface up:

Router(config-if)#no shutdown

Assigning IP address from DHCP:

Router(config-if)# ip address dhcp

Ping to Google DNS server:


Entering GE0/1 Interface:

Router(config)#interface gigabitEthernet 0/1

Assigning IP address :

Router(config-if)#ip address

Making Interface up:

Router(config-if)#no shutdown

Creating DHCP pool:

First go to global configuration mode then

Router(config)#ip dhcp pool mainuser

Router(dhcp-config)#network /24




Static Routing for default Gateway

Router(config)#ip route

Configuring NAT Outside:

Router(config)#interface gigabitEthernet 0/0

Router(config-if)#ip nat outside


Configuring NAT inside:

Router(config)#interface gigabitEthernet 0/1

Router(config-if)#ip nat inside


Creating Access list:

Router(config)#ip access-list standard 1

Router(config-std-nacl)#permit any


Overloading IP NAT inside source to the interface gigabitEthernet 0/0:

Router(config)#ip nat inside source list 1 interface gigabitEthernet 0/0 overload




Cisco #Router_Configuration #IT_Support_People In this video I've demonstrated step by step process how to connect Cisco 2851 Router and Cisco 3560 Switch to ISP Home router and access internet. I also described connection details and configuration of Cisco router using Putty and console cable. IT

Hello All,


I have a CISCO 2800 router and I would like to configure for internet access.


Can someone help me whether the below configuration is correct? Thanks


ip domain name MGM
ip name-server
ip name-server

MGM(config)# interface Ethernet1/0
MGM(config-if)# Description MGM LAN
MGM(config-if)# ip address
MGM(config-if)# ip nat inside
MGM(config-if)# no shutdown
MGM(config-if)# exit

MGM(config)# interface FastEthernet0/0
MGM(config-if)# Description ILL Internet
MGM(config-if)# ip address
MGM(config-if)# ip nat outside
MGM(config-if)# no shutdown
MGM(config-if)# exit

MGM(config)# ip nat inside source list 1 interface FastEthernet0/0 overload
MGM(config)# ip route

MGM(config)# access-list 1 permit


I tried to ping to Local LAN gateway. ( This is in VLAN )

Internet gateway


Please help me.






this looks like a typo:


--> MGM(config)# access-list 1 permit


Make sure the access list says:


MGM(config)# access-list 1 permit


If it still doesn't work, post the full running configuration (sh run)...

Thank you so much for the reply and finding the mistake what I done.


One more question: The scenario is given below.


Internet IP : and gateway is  My router is connected in the airport.

Airport and made Vlan for my company -Vlan


LAN IP is  gateway is


When I configure in my laptop  and trying to PING is not pinging.


Is this not pinging because of typo error I made?  








--> -Vlan

LAN IP is gateway is

When I configure in my laptop and trying to PING is not pinging.


Did you configure that Vlan interface on your router ? Post the running configuration (sh run).

Yes, they have given VLAN IP for my systems in my office.


In between they have fortigate firewall. They are saying they have done the routing and acl in the firewall.


When I configure  two laptops with Vlan IP and connected through switch it is pinging.


But when connect the same through router it is not pinging.


Running configuration, I had pasted in my first post.



I don't see the running configuration (sh run). Either way, where is IP address configured, on your router ?

That is the doubt I have.


I have not configured anywhere, Do I need to configure?

I really don't what I missed here.

Actually, they told me to configure LAN IP as and gateway in the router

Please help me what I should configure.