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TOPIC: Cisco 871 DHCP Configuration with - Cable modem

Cisco 871 DHCP Configuration with - Cable modem 10 years 3 months ago #27895

  • mapena
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I just try to setup this router to works as DHCP with one vlan and one of the interfaces connected to the vlan, I am able to get IP on the laptop and can ping the gateway however I am unable to browse or ping outside the router.
From the router I can ping any ip address.

Here is my config
Cisco 870 - DSL connection
Master#sh run
Building configuration...
Current configuration : 1440 bytes
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname Master
enable secret 5 $1$abIG$nQObBt8phHvc/GE4tzTBD/
no aaa new-model
ip cef
no ip dhcp use vrf connected
ip dhcp excluded-address
ip dhcp pool vlan10
import all
domain-name cisco
dns-server XX.31.64.39 XX.31.112.39
lease 4
ip auth-proxy max-nodata-conns 3
ip admission max-nodata-conns 3
multilink bundle-name authenticated
username xxxxxxx privilege 15 secret 5 xxxxxxxxxx
log config
interface FastEthernet0
switchport access vlan 10
interface FastEthernet1
interface FastEthernet2
interface FastEthernet3
interface FastEthernet4
description External_Connection
mac-address 000f.cba7.952b
ip address dhcp
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
interface Vlan1
no ip address
interface Vlan10
description Internal
ip address
ip nat inside
ip virtual-reassembly
ip forward-protocol nd
ip route XX.XX.XX.XX (ISP gateway)
ip domain name cisco
ip name-server XX.31.64.39
no ip http server
no ip http secure-server
line con 0
no modem enable
line aux 0
line vty 0 4
password xxxxxx
scheduler max-task-time 5000



Re: Cisco 871 DHCP Configuration with - Cable modem 10 years 3 months ago #27898

  • Chris
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You have correctly identified the nat inside and outside interfaces, but you are missing the ip nat command that controls which internal IP address is nat'ed:

Enter the following commands in your configuration and give it another try:

- ip nat inside source list 100 interface fastethernet4 overload
- access-list 100 permit ip any

The above assumes that your Fastethernet 4 interface receives a valid public ip address.

Assuming your default route is valid, you should be able to get your internal clients out.

In case your gateway also perfoms the nat service for you, then simply remove all nat statements from your configuration and you'll get the same result.

Let us know of your results.

Chris Partsenidis.
Founder & Editor-in-Chief

It's working 10 years 3 months ago #27907

  • mapena
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Hi Chris,

I've just added the missing lines and it seems working fine.
Thanks a lot, I spent one week with a headache.

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