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Can't Connect Cisco 1841 router to Internet ( ISP )

USL4054
Beginner
Beginner

I have the following devices for our IT Test LAB

1. Cisco 1841 with 2 Fast Ethernet interfaces fa0/0 & fa0/1

2. Cisco 2960-S

3. Speedstream 6200 DSL Modem  ( PPOE Connection  with Static IP address)

I want to connect to the internet using the current DSL connection we currently have  .

LAPTOP  -->  SWITCH 2960 --> ROUTER 1841 ---> DSL Modem  ---> ISP

Troubleshooting 1:

Currently from the LAPTOP i am able to ping

1. Switch 2960  Vlan interfaces

2. Router 1841  fa0/0  & fa0/1

BUT can not Ping the DSL Modem  LAN interface IP 192.168.2.1 and can not get out to the INTERNET

Troubleshooting 2:

currently from the Switch 2960  i can ping

1. All the Vlan interfaces on the Switch 2960

2. Router  1841  fa0/0 & fa0/1 interfaces

3. Laptop A & B

But can NOT ping the DSL modem LAN interface IP 192.168.2.1 and can not get out to the internet

Troubleshooting 3:

Currently from the Cisco 1841 router  i can ping

1. All the Vlan interfaces on the Switch 2960

2. Router 1841 fa0/0 & fa0/1

3. Laptop A & Laptop B

4. Can Get out to the internet. I am able to ping any  internet destinations without any problem

I really need help. Can someone please help me identify what i am missing as per the configurations and diagram attached. Please make any suggestion that can help

Thank you very much

1 ACCEPTED SOLUTION

Accepted Solutions

Jernej Vodopivec
Enthusiast
Enthusiast

Where is interface GigabitEthernet1/0/2 connected to?

Can you confirm that the modem is acting as a router also? The PPPoE session terminates on modem?

Or you just haven't send that part of configuration - so your 1841 terminates PPPoE on dialer interface?

You should set all interfaces connected to laptops to access port instead of trunk port (switchport mode access). Configure the vlan membership for each port by running "switchport access vlan 100" and "switchport access vlan 200".

You should set interface GigabitEthernet1/0/1 (in case this is the only interface connected to router) to have native vlan something else than 100 and 200)

In case modem is acting as a router you should change

ip route 0.0.0.0 0.0.0.0 FastEthernet0/1

to

ip route 0.0.0.0 0.0.0.0 192.168.2.1

You must add "ip nat inside" to

interface FastEthernet0/0.100 and to

interface FastEthernet0/0.200

You must add "ip nat outside" to

interface FastEthernet0/1

You must create two access lists for NAT:

ip access-list extended VENUS

permit ip 10.10.10.0 0.0.0.255 any

ip access-list extended JUPITER

permit ip 172.21.200 0.0.0.255 any

You must create two NAT rules

ip nat inside source list VENUS interface FastEthernet 0/1 overload

ip nat inside source list JUPITER interface FastEthernet 0/1 overload

Let me know if that helped you.

View solution in original post

11 REPLIES 11

Jernej Vodopivec
Enthusiast
Enthusiast

Where is interface GigabitEthernet1/0/2 connected to?

Can you confirm that the modem is acting as a router also? The PPPoE session terminates on modem?

Or you just haven't send that part of configuration - so your 1841 terminates PPPoE on dialer interface?

You should set all interfaces connected to laptops to access port instead of trunk port (switchport mode access). Configure the vlan membership for each port by running "switchport access vlan 100" and "switchport access vlan 200".

You should set interface GigabitEthernet1/0/1 (in case this is the only interface connected to router) to have native vlan something else than 100 and 200)

In case modem is acting as a router you should change

ip route 0.0.0.0 0.0.0.0 FastEthernet0/1

to

ip route 0.0.0.0 0.0.0.0 192.168.2.1

You must add "ip nat inside" to

interface FastEthernet0/0.100 and to

interface FastEthernet0/0.200

You must add "ip nat outside" to

interface FastEthernet0/1

You must create two access lists for NAT:

ip access-list extended VENUS

permit ip 10.10.10.0 0.0.0.255 any

ip access-list extended JUPITER

permit ip 172.21.200 0.0.0.255 any

You must create two NAT rules

ip nat inside source list VENUS interface FastEthernet 0/1 overload

ip nat inside source list JUPITER interface FastEthernet 0/1 overload

Let me know if that helped you.

Hi Jernej & cadel alain

PPPOE is being terminated at the Speedstream Modem  NOT on the cisco 1841

Cisco 2960 does only inter-VLAN routing and forwards all traffic to Cisco 1841 through a TRUNK .

Gi1/0/1 on Switch 2960 is the TRUNK connecting to cisco 1841 fa0/0 and the Fa0/1 connects to Speedstream modem  ( which has PPOE Terminated on it )

I have modified the configuration as per the suggestion above but i am still getting the same results > No success

=======================================================================


ip subnet-zero
no ip source-route
ip cef
!
ip name-server 192.168.2.1
!

interface FastEthernet0/0
no ip address
no ip redirects
no ip unreachables
no ip proxy-arp
ip route-cache flow
duplex auto
speed auto
no mop enabled
!
interface FastEthernet0/0.100
description JUPITER-VLAN
encapsulation dot1Q 100
ip address 172.21.200.1 255.255.255.0
ip nat inside
ip virtual-reassembly
no snmp trap link-status
!
!
interface FastEthernet0/0.200
description VENUS-VLAN
encapsulation dot1Q 20
ip address 10.10.10.1 255.255.255.0
ip nat inside
ip virtual-reassembly
no snmp trap link-status
!

!
interface FastEthernet0/1
ip address 192.168.2.20 255.255.255.0
ip nat inside
ip virtual-reassembly
duplex auto
speed auto
!
ip route 0.0.0.0 0.0.0.0 192.168.2.1
!
!
ip nat inside source list JUPITER interface FastEthernet0/1 overload
!
ip nat inside source list VENUS interface FastEthernet0/1 overload
!
ip access-list extended JUPITER
permit ip 172.21.202.0 0.0.0.255 any
!
!
ip access-list extended VENUS
permit ip 10.10.10.0 0.0.0.255 any
!
!
===================================Catalyst 2960-S===================

!
ip routing
!
interface GigabitEthernet1/0/1
switchport trunk native vlan 920
switchport mode trunk
!
interface GigabitEthernet1/0/2
switchport access vlan 100
switchport mode access
!
the rest is truncated
!
interface Vlan100
description JUPITER-VLAN
ip address 172.21.200.2 255.255.255.0
!
interface Vlan200
description VENUS-VLAN
ip address 10.10.10.2 255.255.255.0
!
ip route 0.0.0.0 0.0.0.0 172.21.200.1
!
!
the rest is truncated

------------------------------------------------------------