Solved: how do you connect a cisco router to the internet through a cable modem/ router gateway - Page 8

breynold76 · ‎04-27-2013

I have searched on here but can't find the exact answer i am looking for. I have a cisco 1760 router and a 2950 switch. The router has an ethernet wic card added so i have two ethernet connections available. I would like to connect the cable modem gatway to the router through one of the ethernet connections on the router and then to the switch. I cannot seem to get this setup to work. There are several different ways i have seen posted to accomlish this. dhcp, no dhcp, creating a seperate network, and giving the e0/0 an ip address within the range of the cable gateways network addresses. None of this has worked. Can anybody post the commands that need to be entered on the router to make this possible?

breynold76 · ‎05-01-2013

I am not an expert at this but, my guess is that the switch is sending an internet signal from the modem through the switch and anything connected to the switch is picking up an ip address from the modem. What is strange though is that yesterday i could successfully ping everything even though the pc had an ip address from the modem not the cisco router at that time as well.

pc to modem

pc to cisco router

cisco router to pc

cisco router to modem

I could even ping from the cisco router to my laptop that is on wifi.

The only thing that changed that i know of is i added a default route.

Richard Burts · ‎05-01-2013

The suggestion was to configure vlans in the switch and to have one vlan for connecting the router, the cable modem, and anything that needs to be logically connected on the "outside". The second vlan would be for the LAN, for all the devices that are logically "inside".

It sounds like the device that is running the TFTP server is connected in the vlan for outside. And given the difficulties we experienced with communications from the router to outside devices I suspect this is the reason that the TFTP is not working. I suggest that we get the TFTP server into the inside vlan. I am not sure whether that suggests changing the configuration of the switch or suggests being more careful about what port the device is plugged into.

HTH

Rick

HTH

Rick

breynold76 · ‎05-01-2013

I tried directly connecting the computer to the fa0/0 port on the router and it would not give out an ip address.

for the other suggestion i have tried multiple ports on the switch and apparently all of them give out the same ip address 192.168.0.4

Richard Burts · ‎05-01-2013

It has been a while since we have looked at the switch and I am not sure if anything there might have changed. So could you post a new copy of the configuration of the switch?

HTH

Rick

HTH

Rick

breynold76 · ‎05-01-2013

Switch#show run

Building configuration...

Current configuration:

!

version 12.0

no service pad

service timestamps debug uptime

service timestamps log uptime

no service password-encryption

!

hostname Switch

!

ip subnet-zero

!

interface FastEthernet0/1

!

interface FastEthernet0/2

!

interface FastEthernet0/3

!

interface FastEthernet0/4

!

interface FastEthernet0/5

!

interface FastEthernet0/6

!

interface FastEthernet0/7

!

interface FastEthernet0/8

!

interface FastEthernet0/9

!

interface FastEthernet0/10

!

interface FastEthernet0/11

!

interface FastEthernet0/12

!

interface FastEthernet0/13

!

interface FastEthernet0/14

!

interface FastEthernet0/15

!

interface FastEthernet0/16

!

interface FastEthernet0/17

!

interface FastEthernet0/18

!

interface FastEthernet0/19

!

interface FastEthernet0/20

!

interface FastEthernet0/21

!

interface FastEthernet0/22

!

interface FastEthernet0/23

description ##link to modem##

switchport access vlan 100

!

interface FastEthernet0/24

description ##trunk to router##

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 1,100,1002-1005

switchport mode trunk

!

interface FastEthernet0/25

!

interface FastEthernet0/26

!

interface FastEthernet0/27

!

interface FastEthernet0/28

!

interface FastEthernet0/29

!

interface FastEthernet0/30

!

interface FastEthernet0/31

!

interface FastEthernet0/32

!

interface FastEthernet0/33

!

interface FastEthernet0/34

!

interface FastEthernet0/35

!

interface FastEthernet0/36

!

interface FastEthernet0/37

!

interface FastEthernet0/38

!

interface FastEthernet0/39

!

interface FastEthernet0/40

!

interface FastEthernet0/41

!

interface FastEthernet0/42

!

interface FastEthernet0/43

!

interface FastEthernet0/44

!

interface FastEthernet0/45

!

interface FastEthernet0/46

!

interface FastEthernet0/47

!

interface FastEthernet0/48

!

interface GigabitEthernet0/1

!

interface GigabitEthernet0/2

!

interface VLAN1

no ip directed-broadcast

no ip route-cache

!

line con 0

transport input none

stopbits 1

line vty 5 15

!

end

Richard Burts · ‎05-01-2013

Thank you for the prompt response. Now would you post the output from the switch of the command show vlan

HTH

Rick

HTH

Rick

breynold76 · ‎05-01-2013

Switch#show vlan

VLAN Name Status Ports

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

1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4,

Fa0/5, Fa0/6, Fa0/7, Fa0/8,

Fa0/9, Fa0/10, Fa0/11, Fa0/12,

Fa0/13, Fa0/14, Fa0/15, Fa0/16,

Fa0/17, Fa0/18, Fa0/19, Fa0/20,

Fa0/21, Fa0/22, Fa0/25, Fa0/26,

Fa0/27, Fa0/28, Fa0/29, Fa0/30,

Fa0/31, Fa0/32, Fa0/33, Fa0/34,

Fa0/35, Fa0/36, Fa0/37, Fa0/38,

Fa0/39, Fa0/40, Fa0/41, Fa0/42,

Fa0/43, Fa0/44, Fa0/45, Fa0/46,

Fa0/47, Fa0/48, Gi0/1, Gi0/2

100 INTERNET active Fa0/23

1002 fddi-default active

1003 token-ring-default active

1004 fddinet-default active

1005 trnet-default active

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2

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

1 enet 100001 1500 - - - - - 0 0

100 enet 100100 1500 - - - - - 0 0

1002 fddi 101002 1500 - - - - - 0 0

1003 tr 101003 1500 - - - - - 0 0

1004 fdnet 101004 1500 - - - ieee - 0 0

1005 trnet 101005 1500 - - - ibm - 0 0

Bilal Nawaz · ‎05-01-2013

The modem should be plugged in to fa0/23

The router should be plugged in to fa0/24

You can plug your PC in to fa0/1
If this is the case already, Next thing to check will be the router config please.

Hope this helps

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Richard Burts · ‎05-01-2013

Thank you for the outputs. I thought that the symptoms where the PC running tftp is receiving an IP from the cable modem suggested that perhaps the vlans were not operating as we intended. But this output verifies that vlan 100 does exist and is running on Fast0/23. It does not show here but it seems correct that Fast0/24 is a trunk carrying the vlans. Perhaps we can verify this is you would post the output from the switch of show interface trunk

The other thing that occurs to me is that perhaps we should be clear about what device is plugged into what port of the switch, especially for the cable modem, the router, and the PC running TFTP. Can you tell us those specific interface connections? The symptoms would make sense if the cable modem were plugged in somewhere other than Fast0/23.

HTH

Rick

HTH

Rick

breynold76 · ‎05-01-2013

I had the modem in fa0/24

the router was in fa0/23

pc is in fa0/1

i changed it so it was as you suggested.

modem in fa0/23

router in fa0/24

once i did that i lost internet connectivity and i cannot ping the cisco router anymore.

here is the message i get when entering the command show interface trunk

Switch#show interface trunk

^

% Invalid input detected at '^' marker.

breynold76 · ‎05-01-2013

the router config

R1#show config

Using 1635 out of 29688 bytes

!

! Last configuration change at 04:34:10 UTC Wed Jul 30 2008

! NVRAM config last updated at 12:12:16 UTC Wed Jul 30 2008

!

version 12.3

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname R1

!

boot-start-marker

boot-end-marker

!

no logging console

!

mmi polling-interval 60

no mmi auto-configure

no mmi pvc

mmi snmp-timeout 180

no aaa new-model

ip subnet-zero

ip cef

!

ip dhcp excluded-address 192.168.1.0 192.168.1.99

ip dhcp excluded-address 192.168.0.0 255.255.255.0

ip dhcp excluded-address 192.168.0.0 192.168.0.99

!

ip dhcp pool MY_LAN

network 192.168.0.0 255.255.255.0

default-router 192.168.0.1

dns-server 192.168.0.1

!

ip name-server 24.217.0.5

ip name-server 8.8.8.8

ip name-server 192.168.0.1

no ftp-server write-enable

!

interface FastEthernet0/0

no ip address

speed auto

!

interface FastEthernet0/0.1

description ##my lan##

encapsulation dot1Q 1 native

ip address 192.168.1.1 255.255.255.0

ip nat inside

!

interface FastEthernet0/0.100

description ##internet##

encapsulation dot1Q 100

ip address 192.168.0.101 255.255.255.0

ip access-group MY_WAN in

ip nat outside

!

interface Serial0/0

no ip address

shutdown

!

interface Serial0/1

no ip address

shutdown

!

ip nat inside source list MY_LAN interface FastEthernet0/0.100 overload

ip classless

no ip http server

!

ip access-list standard MY_LAN

permit 192.168.1.0 0.0.0.255

!

ip access-list extended MY_WAN

permit tcp any any established

deny tcp any any

permit ip any any

!

line con 0

password cisco

login

line aux 0

line vty 0 4

password cisco

login

!

end

Richard Burts · ‎05-01-2013

If the cable modem was in port Fast0/24 then it was in the port configured as trunk and would have access to vlan 1. And that explains why the PC was getting addresses from the cable modem.

And with the router in Fast0/23 then it was isolated in vlan 100 and could not talk to anything.

I am puzzled why things stopped working when you connected the devices to the correct ports. Perhaps it might help if you power cycle the devices after they are connected in the correct ports?

HTH

Rick

HTH

Rick

Bilal Nawaz · ‎05-01-2013

Hello rick, things stopped working because DHCP is incorrect. Please review the config.

I already suggested a working config for router on a stick and dhcp before. But seems to have been changed now.

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Bilal Nawaz · ‎05-01-2013

To keep things simple please change the config as below:

ip dhcp excluded-address 192.168.1.0 192.168.1.99
No ip dhcp excluded-address 192.168.0.0 255.255.255.0
No ip dhcp excluded-address 192.168.0.0 192.168.0.99
!
ip dhcp pool MY_LAN
network 192.168.1.0 255.255.255.0
default-router 192.168.1.1
dns-server 192.168.0.1

After this, you should be able to get an IP address from the Cisco router and be able to ping. Then we can proceed with getting that IOS image off of that flash.

Hope this helps

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Richard Burts · ‎05-01-2013

Yes you are correcct about that. I see it now in the config that the DHCP pool is changed so that it overlaps with the cable modem pool. And there is no pool for vlan 1.

HTH

Rick

HTH

Rick