12-31-2012 02:06 PM - edited 03-07-2019 10:50 AM
I've recently acquired a Cisco 1841 from a school that was upgrading their network. Although, I have a computing background, I am totally new to networking.
I can't seem to get this thing set up. I can't find a manual online, just a brochure and a few very specific guides here and there. I've managed to reset the router (I think) and enter the initial configuration, but I can't seem to be able to save the configuration or get any further. I can only access it with one of those blue console cables.
Basically what I want to do:
Configure FastEthernet0/0 to connect to a cable modem or other wan (like an apartment ethernet jack) that uses dhcp.
Configure FastEthernet0/1 to act as a router/gateway/dhcp server for a personal class c network.
Make it moderately secure for a home network, but nothing fancy.
If at all possible, I also want to do:
Configure port forwarding to a server on my network.
Configue Dynamic DNS.
I want to use the 1841 to replace a wrt54g as my home router and use the wrt54g as an access point.
I know it's annoying to be asked to explain this in layman's terms, but I don't know where else to turn. I appreciate any help.
Solved! Go to Solution.
01-07-2013 04:44 PM
It possibly could be that you have hard coded your speed and duplex on your WAN interface.
Try setting them back to auto.
Interface fa 0/1
Speed auto
Duplex auto
If you can't set this on both sides for the cable I would recommend that you leave it on auto/auto.
I'm not sure what your LAN interface connects to but unless it is hard coded on the other side you should change it back
You might have just gotten lucky that your Netgear router was able to negotiate the speed. But at the same time it might have defaulted to 10/half because it tried to negotiate but didn't hear anything from the other side.
Let me know how this works. If you need some help with basic CBAC firewall configuration let me know.
Elton
Sent from Cisco Technical Support iPhone App
01-07-2013 12:39 PM
Hello Alex,
There is a much more detailed configuration guide available at:
It includes sections on setting up the DHCP server and your WAN connection.
Hopefully that will tell you what you need to know,
Christopher Ebert
Network Support Engineer - Cisco Small Business Support Center
01-07-2013 01:00 PM
It is not 1841, it is 881 but will give you some idea:
01-07-2013 01:22 PM
Chris,
Please let us know how far you have got and I can help walk you through problems you are having.
Thanks, Elton
Sent from Cisco Technical Support iPhone App
01-07-2013 03:24 PM
Actually, my config was good. For some reason the modem would not play nice with eachother. I connected a cheap netgear home router with a class c net to the modem, then switched my 1841 to class b before connecting it to the cheap router. I can get an internet connection now, but I had to put the netgear in between. Any ideas why?
01-07-2013 03:29 PM
Could you post your configuration? I have a feeling something isn't quite right and if it is I can hopefully lead you in the right direction. An 1841 router should connect to a modem just fine.
What kind of modem is it?
Elton
Sent from Cisco Technical Support iPhone App
01-07-2013 04:24 PM
Surfboard SB5101
[code]
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname STARDOCK
!
boot-start-marker
boot-end-marker
!
no logging console
enable secret 5 XXXXXXXXXXXXXXXXXXXXXX
enable password XXXXXXXXXXX
!
ip subnet-zero
no ip finger
ip dhcp excluded-address
!
ip dhcp pool SPACEDOCKDHCP
network
default-router
dns-server
!
!
!
username XXXXXXXXX privilege 15 password 0 XXXXXXXXX
archive
log config
hidekeys
!
!
interface FastEthernet0/1
description WANPORT
ip address dhcp
ip nat outside
speed 100
full-duplex
!
interface FastEthernet0/0
description LANPORT
ip address
ip nat inside
speed 100
full-duplex
!
interface Serial0/0/0
no ip address
no ip route-cache
shutdown
no fair-queue
!
!
ip nat inside source list 1 interface FastEthernet0/1 overload
ip classless
ip http server
ip http authentication local
ip http secure-server
!
access-list 1 permit
!
!
line con 0
line aux 0
line vty 0 4
password XXXXXXXXXX
login
!
end
[/code]
01-07-2013 04:44 PM
It possibly could be that you have hard coded your speed and duplex on your WAN interface.
Try setting them back to auto.
Interface fa 0/1
Speed auto
Duplex auto
If you can't set this on both sides for the cable I would recommend that you leave it on auto/auto.
I'm not sure what your LAN interface connects to but unless it is hard coded on the other side you should change it back
You might have just gotten lucky that your Netgear router was able to negotiate the speed. But at the same time it might have defaulted to 10/half because it tried to negotiate but didn't hear anything from the other side.
Let me know how this works. If you need some help with basic CBAC firewall configuration let me know.
Elton
Sent from Cisco Technical Support iPhone App
01-07-2013 05:14 PM
I have since moved to my dorm so I'm using their wan. I had the same problem until I just tried what you showed me. Works fine now thanks. I think I will hold off a while on a firewall. My only concern is keeping school personel out. Housing posseses a key, and my router has been tampered with before. I need to get my other switches wotking first.
01-07-2013 05:57 PM
I would recommend that you add local authentication to your console port. Similar to what you did on the VTY lines for telnet access.
Another recommendation I can make for this is to create an access list for your VTY lines only allowing access from your local LAN. This way you can only relent to the router from your local LAN and someone from the outside, on the campus WAN couldn't connect to the router.
Currently anyone with a console cable could come and plug into the router and have access to it.
Let me know of you need help with this
Elton
Sent from Cisco Technical Support iPhone App
01-07-2013 06:05 PM
I think I can figure it out. Thank you for your help.
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