how do you connect a cisco router to the internet through a cable modem/ router gateway

[breynold76]

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?

[Richard Burts]

Those are the two most important commands. I wonder if there might be some commands on the interface left over from a previous use of the router. Perhaps you can post the running configuration of the router and also the output of show interface fa0/0?

It also occurs to me that I have had experiences where a cable modem does not react well when you change the MAC address of the device that it connects to. It might be helpful to connect the router and then to power cycle the cable modem.

HTH

Rick

[breynold76]

I power cycled the cable modem but it did not bring up an ip address on the cisco router.

R1#show run

Building configuration...

Current configuration : 672 bytes

!

! Last configuration change at 00:47:09 UTC Tue Jul 29 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

!

!

mmi polling-interval 60

no mmi auto-configure

no mmi pvc

mmi snmp-timeout 180

no aaa new-model

ip subnet-zero

ip cef

!

!

!

no ftp-server write-enable

!

!

!

!

interface FastEthernet0/0

ip address dhcp

speed auto

!

interface Serial0/0

no ip address

shutdown

!

interface Serial0/1

no ip address

shutdown

!

ip classless

no ip http server

!

!

line con 0

password cisco

login

line aux 0

line vty 0 4

password cisco

login

!

!

end

R1#show int fa0/0

FastEthernet0/0 is up, line protocol is up

  Hardware is PQUICC_FEC, address is 000f.24af.5c2d (bia 000f.24af.5c2d)

  Internet address will be negotiated using DHCP

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s, 100BaseTX/FX

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:24, output 00:00:01, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     712 packets input, 59145 bytes

     Received 442 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog

     0 input packets with dribble condition detected

     115 packets output, 30432 bytes, 0 underruns

     3 output errors, 0 collisions, 2 interface resets

     0 babbles, 0 late collision, 0 deferred

     3 lost carrier, 0 no carrier

     0 output buffer failures, 0 output buffers swapped out

[Bilal Nawaz]

I just tried this scenario with a linksys WRT and an 1801 and managed to pick up an address and my default route, did this just to make sure that there's nothing that is obviously wrong.

We know that the PCs work, so it must be something about the routers that the modem doesn't quite like.

I'd be really tempted to put an IP address manually within the 192.168.0.0/24 range and ping the modem to see if it responds, what are your thoughts on this Rick?

But before we try that,
Can we enable debugging on the router while we reboot the modem please?

Debug ip dhcp server packet
Debug ip dhcp server events
Debug ip packet

And then reload the modem.

Hope this will show us something more...

Are we able to see anything on the Motorola? Does it have some sort of GUI that we could browse to for management?

Sent from Cisco Technical Support iPhone App

[Richard Burts]

The config looks good and the output of show interface looks good. I am encouraged that the counter for intput packets and for output packets show that there is some traffic going back and forth.

You might try adding this

config t

service dhcp

If that does not make a difference then would you also post the output of show ip interface fa0/0

HTH

Rick

[Richard Burts]

I agree that it is worth trying to configure a static address within the range and see if the router and the modem will communicate.

HTH

Rick

[breynold76]

I entered the debug commands, then restarted the cable modem. I own the modem not the cable company so for the most part i have access to all settings in the gui. just let me know what settings you want to look at.

R1#debug ip dhcp server packet

R1#debug ip dhcp server events

R1#

Jul 29 01:15:15.730: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:15:18.730: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:15:21.731: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:15:30.926: DHCPD: checking for expired leases.

Jul 29 01:16:36.109: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:16:39.110: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:16:42.111: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:16:52.312: IP: s=192.168.0.4 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:16:55.309: IP: s=192.168.0.4 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:17:30.927: DHCPD: checking for expired leases.

Jul 29 01:17:56.493: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:17:59.494: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:18:02.495: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:18:16.702: IP: s=192.168.0.2 (FastEthernet0/0), d=255.255.255.255, len 335, rcvd 2

Jul 29 01:18:34.700: IP: s=192.168.0.2 (FastEthernet0/0), d=255.255.255.255, len 335, rcvd 2

Jul 29 01:19:02.229: IP: s=192.168.0.12 (FastEthernet0/0), d=255.255.255.255, len 96, rcvd 2

Jul 29 01:19:03.415: IP: s=192.168.0.12 (FastEthernet0/0), d=255.255.255.255, len 96, rcvd 2

Jul 29 01:19:04.677: IP: s=192.168.0.12 (FastEthernet0/0), d=255.255.255.255, len 96, rcvd 2

Jul 29 01:19:09.004: IP: s=0.0.0.0 (FastEthernet0/0), d=255.255.255.255, len 336, rcvd 2

Jul 29 01:19:10.002: IP: s=192.168.0.1 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:19:14.024: IP: s=192.168.0.5 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:19:16.877: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:19:17.021: IP: s=192.168.0.5 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:19:19.878: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:19:22.879: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:19:30.928: DHCPD: checking for expired leases.

Jul 29 01:20:06.029: IP: s=192.168.0.5 (FastEthernet0/0), d=255.255.255.255, len 330, rcvd 2

Jul 29 01:20:07.019: IP: s=192.168.0.1 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:20:37.269: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:20:40.270: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:20:43.270: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:21:10.279: IP: s=192.168.0.5 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:21:13.280: IP: s=192.168.0.5 (FastEthernet0/0), d=255.255.255.255, len 328, rcvd 2

Jul 29 01:21:30.929: DHCPD: checking for expired leases.

Jul 29 01:21:57.652: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:22:00.653: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

Jul 29 01:22:03.654: IP: s=0.0.0.0 (local), d=255.255.255.255 (FastEthernet0/0), len 604, sending broad/multicast

R1#no debug all

All possible debugging has been turned off

[Richard Burts]

I am curious about the number of source addresses in 192.168.0 that show up in the debug. Are there multiple devices connected via the 4 ports of the cable modem? If so would it be feasible to set up a test where the router is the only device that is connected to the cable modem?

Have you tried my suggestion about service dhcp?

HTH

Rick

[breynold76]

i missed the service dhcp but just entered the commands for it. all 4 ports are used up and i also have a monoprice switch installed for all the devices we have in the living room. i can disconnect everything and try. also i put in a static address of 192.168.0.101 and i can now succesfully ping the cable modem but cannot ping the dns server 8.8.8.8 on the cisco router or the dns server setup by charter for the cable modem 24.217.0.5

[Richard Burts]

It is good to know that with a static address that you can ping the cable modem.

If you can not ping either of the DNS addresses then it sounds like the cable modem is not doing address translation for your address. Perhaps the cable modem has some logic that it will only translate for addresses that it has assigned?

I would like to have a test where the router is the only device connected to the cable modem. And perhaps a power cycle of the cable modem at the beginning of that test.

HTH

Rick

[Bilal Nawaz]

Awesome! so there's connectivity - however, no DHCP ip address being handed down to the router... We also know that the modem does not allow us to ping outbound to the internet...

Im going through the manual for the motorola - here it is so we can take a look and see if there is anything we can do on there... Not anything that is apparent that I can see though

http://www.motorola.com/on/demandware.static/Sites-Site/Sites-Motorola_US-Library/default/v1335985434876/Promotion/cross-sell/cable-modem/SURFboard_SBG6580_UserGuide.pdf?version=1,336,493,317,000

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[breynold76]

ok nothing is connected to the cable modem but the cisco router. ping to the dns address still fails

[Richard Burts]

While the router is the only device connected to the cable modem can we configure the router to use DHCP to learn its address on FA0/0?

HTH

Rick

[Bilal Nawaz]

I wonder if there is a list of 'trusted computers'

http://portforward.com/english/routers/firewalling/Motorola/SBG6580/defaultguide.htm

Or maybe we could create a DHCP reservation for the Router?

http://www.phonepower.com/wiki/How_to_Configure_a_Motorola_SBG6580_Wireless_Cable_Modem_to_function_with_the_Grandstream

Or we could try Bridged mode?

http://fascinated.fm/post/2379188731/getting-a-motorola-sbg6580-into-bridge-mode-on

There must be a reason why its not giving out DHCP to the router. And must be a reason why its not allowing out to the internet.

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[breynold76]

I configured fa0/0 with dhcp and power cycled the cable modem.

R1(config-if)#do show ip int brief

Interface                  IP-Address      OK? Method Status                Protocol

FastEthernet0/0            unassigned      YES DHCP   up                    up

Serial0/0                  unassigned      YES unset  administratively down down

Serial0/1                  unassigned      YES unset  administratively down down

R1(config-if)#

[Richard Burts]

I am puzzled why the DHCP is not working and wonder if there is some configuration option that we missed. Would you post the output of these commands in global configuration mode

service  ?

service dhcp  ?

Also can you post the output of show version for the router.

HTH

Rick