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1841 on a roadrunner modem

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May 21st, 2007
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I am setting up a 1841 router that the client already has with a low cost roadrunner cable connection. the 1841 he has was from a previous vendor with a T1. The 1841 does not have the cable modem card in it. I have tried quite a few things and I will attempt to list them. Firstly, I ensured the cable modem doesn't hold MAC addresses - I have connected my laptop to it and a Linksys router, and both times I recieve a WAN IP and can browse the intarweb.

I connected the modem to FE0/1 of the 1841 router, ensured it's admin up (pretty lights), set it to DHCP, but when I issue the "show ip interface brief" FE0/0 has my internal IP address, but FE0/1 isn't getting an IP. I thought that would be the simple part. before I did any of this, I formated flash, and loaded a new IOS onto the 1841 (c1841-adventerprisek9-mz.124-13a.bin). What am I missing?

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Richard Burts Mon, 05/21/2007 - 12:45
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Joe


Some additional detail would be helpful. Can you post the output of show run interface fast0/1 and the output of show interface fast0/1?


The 1841 certainly should be able to talk to the cable modem and to get an IP address. Are there possibly speed and/or duplex issues?


HTH


Rick

Richard Burts Fri, 05/25/2007 - 13:51
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Joe


Thanks for posting the additional information. I have looked at it and I do not see anything obvious that would explain the difficulty. I do have a couple of suggestions of things to try.

- I would like to see what happens if you remove this line:

ip broadcast-address 0.0.0.0

- I wonder about the interface speed as 100 Mb. I see the interface is configured for speed auto, but I wonder if the roadrunner is really doing 100 Mb. When you connect your PC and things work, could you check the Ethernet interface and verify what its speed is?

- I am not sure why you specify full duplex on the fast0/1 interface and suggest that you put duplex to auto.

- I wonder what would happen if you change fast0/1 to ip address dhcp (but without specifying the client-id)

- I would also suggest that you remove this line from fast0/1:

ip verify unicast source reachable-via rx allow-default 100


Give these a try (probably best to do one at a time) and let us know what happens.


HTH


Rick

foxbatreco Sun, 05/27/2007 - 15:09
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Hii..

As i can understand frm the post, u were able to access internet with linksys and cable modem , but not with 1841 when attached to CM ..rt??

The possible problem could be due to arp bindings on the cable modem.Ask ur provider to clear the current arp bindings for the modem (i.e with the linksys router) ...which doesnt allow data to be passed .

Pls do let us know of the outcome and rate the post if it helps.

joebagodoe Sun, 05/27/2007 - 18:10
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Thank you for your suggestions. I will see if they work.

I have also connected the outside interface to our local network so I could see if it would receive DHCP from our server. It would not. I will post again after I look at those settings.

joebagodoe Mon, 05/28/2007 - 13:10
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I tried the suggestions and nothing is helping. I have even flashed the ios to 12.4.13b, but it is not the problem. I have erased nv and started over with a fresh config, I have even followed the cisco guide (http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt1/1cfdhcp.htm)... it just won't pick up an IP. I am at a loss. I have absolutely no idea what is wrong. do I need a loopback or something? ARRG!

Attached is my run and int fa0/0 configs

Thanks for helping with this, I really need it!



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paolo bevilacqua Mon, 05/28/2007 - 14:07
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Hi,


as suggested before, can you remove ip broadcast address 0.0.0.0 and all dhcp optoinal settings, do "term mon", then "debug ip dhcp" ?



joebagodoe Mon, 05/28/2007 - 15:40
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I removed the broadcast from 0/1, but I cannot for some reason remove it from 0/0. Is there a better way of doing it than "no ip broadcast-address 0.0.0.0"?

Here is the result from the debug:

Router#debug dhcp

DHCP client activity debugging is on

Router#

*May 29 00:34:36.871: DHCP: deleting entry 637D7C58 0.0.0.0 from list

*May 29 00:35:06.503: DHCP: Try 133 to acquire address for FastEthernet0/0

*May 29 00:35:06.515: DHCP: allocate request

*May 29 00:35:06.515: DHCP: new entry. add to queue, interface FastEthernet0/0

*May 29 00:35:06.515: DHCP: SDiscover attempt # 1 for entry:

*May 29 00:35:06.515: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 00:35:06.515: DHCP: SDiscover 295 bytes

*May 29 00:35:06.515: B'cast on FastEthernet0/0 interface from 0.0.0

.0

*May 29 00:35:09.871: DHCP: SDiscover attempt # 2 for entry:

*May 29 00:35:09.871: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 00:35:09.871: DHCP: SDiscover 295 bytes

*May 29 00:35:09.871: B'cast on FastEthernet0/0 interface from 0.0.0

.0

*May 29 00:35:13.871: DHCP: SDiscover attempt # 3 for entry:

*May 29 00:35:13.871: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 00:35:13.871: DHCP: SDiscover 295 bytes

*May 29 00:35:13.871: B'cast on FastEthernet0/0 interface from 0.0.0

.0%Unknown DHCP problem.. No allocation possible

*May 29 00:35:26.995: DHCP: Waiting for 60 seconds on interface FastEthernet0/0


paolo bevilacqua Mon, 05/28/2007 - 15:51
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Hi,


please try:

ip broadcast-addresss 255.255.255.255


Alos please do clear counters and check that input packets is going up, as in the debug above seem like there is no answer to DCHP discovery.

joebagodoe Mon, 05/28/2007 - 17:09
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I put that in, checked running-config, and the broadcast address line was gone. It then came back when it checked for DHCP server availability again.


It looks like the attempt count is increasing, but for some reason it still can't see my win2k3 DHCP server.


----LOG----

Router#clear counters

Clear "show interface" counters on all interfaces [confirm]

Router#

*May 29 01:47:56.854: %CLEAR-5-COUNTERS: Clear counter on all interfaces by cons

olede

Router#debug dhcp

DHCP client activity debugging is on

Router#

*May 29 01:48:23.886: DHCP: deleting entry 63B9823C 0.0.0.0 from list

*May 29 01:48:53.574: DHCP: Try 188 to acquire address for FastEthernet0/0

*May 29 01:48:53.586: DHCP: allocate request

*May 29 01:48:53.586: DHCP: new entry. add to queue, interface FastEthernet0/0

*May 29 01:48:53.586: DHCP: SDiscover attempt # 1 for entry:

*May 29 01:48:53.586: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:48:53.586: DHCP: SDiscover 295 bytes

*May 29 01:48:53.586: B'cast on FastEthernet0/0 interface from 0.0.0.0

*May 29 01:48:56.886: DHCP: SDiscover attempt # 2 for entry:

*May 29 01:48:56.886: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:48:56.886: DHCP: SDiscover 295 bytes

*May 29 01:48:56.886: B'cast on FastEthernet0/0 interface from 0.0.0.0

*May 29 01:49:00.886: DHCP: SDiscover attempt # 3 for entry:

*May 29 01:49:00.886: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:49:00.886: DHCP: SDiscover 295 bytes

*May 29 01:49:00.886: B'cast on FastEthernet0/0 interface from 0.0.0.0%Unknown DHCP problem.. No allocation possible

*May 29 01:49:14.066: DHCP: Waiting for 60 seconds on interface FastEthernet0/0

*May 29 01:49:44.886: DHCP: deleting entry 63B9823C 0.0.0.0 from list

*May 29 01:50:14.066: DHCP: Try 189 to acquire address for FastEthernet0/0

*May 29 01:50:14.078: DHCP: allocate request

*May 29 01:50:14.078: DHCP: new entry. add to queue, interface FastEthernet0/0

*May 29 01:50:14.078: DHCP: SDiscover attempt # 1 for entry:

*May 29 01:50:14.078: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:50:14.078: DHCP: SDiscover 295 bytes

*May 29 01:50:14.078: B'cast on FastEthernet0/0 interface from 0.0.0.0

*May 29 01:50:17.886: DHCP: SDiscover attempt # 2 for entry:

*May 29 01:50:17.886: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:50:17.886: DHCP: SDiscover 295 bytes

*May 29 01:50:17.886: B'cast on FastEthernet0/0 interface from 0.0.0.0

*May 29 01:50:21.886: DHCP: SDiscover attempt # 3 for entry:

*May 29 01:50:21.886: DHCP: SDiscover: sending 295 byte length DHCP packet

*May 29 01:50:21.886: DHCP: SDiscover 295 bytes

*May 29 01:50:21.886: B'cast on FastEthernet0/0 interface from 0.0.0.0%Unknown DHCP problem.. No allocation possible

*May 29 01:50:34.558: DHCP: Waiting for 60 seconds on interface FastEthernet0/0

paolo bevilacqua Mon, 05/28/2007 - 19:05
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Hello,


In my experience, when the router gets no reply to dhcp discover, is because the server is not offering an address. You may want to check with ethereal that the server is actually sending a reply to the router.

joebagodoe Tue, 05/29/2007 - 05:59
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I set fa0/0 static to 192.168.0.3, and then set fa0/1 static to 192.168.0.4, and attempted to no shut fa0/1 and got this error:

% 192.168.0.0 overlaps with FastEthernet0/0

FastEthernet0/1: incorrect IP address assignment


I shut fa0/0 and no shut fa0/1 and could ping 192.168.0.4. I shut fa0/1 and no shut fa0/0 and could ping 192.168.0.3. So obviously there is a problem with a vlan or something? I'm running srvr 2k3 at home for DNS, domain, DHCP, and it is up and fine. It's address is 192.168.0.2. I'm on it right now and just released/renewd my IP.

paolo bevilacqua Tue, 05/29/2007 - 06:02
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Hello,


router ports in the router must fall in different subnets, so the overlap warning you are receiving is correct. So if you want 192.168.0/24 on the "inside", on the "outside" there should be some other address.

joebagodoe Tue, 05/29/2007 - 06:05
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I was able to obtain a Cisco uBR905 cable modem and will try to get it up and running. At this point, it just seems that the cisco router cannot find the broadcast or isn't broadcasting the follow up DHCP request to my server. Maybe an actual cisco modem will do better.

joebagodoe Tue, 05/29/2007 - 07:39
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Here are the results of the Ethereal capture. I disabled DHCP on 192.168.0.2 (Win2k3 server) and enabled it on 192.168.0.1 (wrt54g router), but it still isn't obtaining an IP.



paolo bevilacqua Tue, 05/29/2007 - 08:25
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Hello,


I see the reply from dhcp server on linksys and it appears OK. Not sure why the router is not accepting it. Sometime I've seen router having some difficulty in accepting the address, but eventually it worked in any case.

Do you get a different address each time on the cablemodem, or it is always the same so that you can configure it statically in the router ?

joebagodoe Tue, 05/29/2007 - 11:24
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The IP on the cable modem is dynamic. He really doesn't want to upgrade to a static yet since he's not hosting anything.

I can't believe this is kicking my ass. This should be simple, but it just isn't working. I've checked for ios compatibility, and it's running 12.4.13b, which is an acceptable 1841 router ios.

I wish I could submit a bug report to cisco, but I don't have an actual account.

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