Cisco 1841 not routing between interfaces

[silviu1983]

Hy guys,

I have a question that has been bugging me for some time now

I have an CISCO router 1841 with 2 interfaces F0/1 and F0/0 and for testing purposes i have it in my LAN at home. The problem is though, in Packet Tracer I create 4 LANs all wired together with the 4 routers(1841) and i get to ping from one end to another . I configure the interfaces and all is good. However when I physically connect my 1841 router in my LAN , I cannot get past the router.

The layout is like this:

1. My TP LINK router that is directlly connected to the internet and acts as a DNS server and GATEWAY

2. The CISCO router in between the PC and the GATEWAY connected to F0/1 (192.168.1.x/24 NETWORK)

3. The PC that I use for daily tasks that is directlly connected to the F0/0 (10.90.0.X/24 NETWORK) of the router

Now, the problem I have is this:

From the PC I can ping F0/0 of the router and even F0/1 , but when I try to go beyond the router (to my GATEWAY) I get no reply back.

I have no ACL set in place on the router . The only thing I configured is the IP, MASK. I have tryed with static routes, default routes,( which I dont see the point because the router is directlly connected to both networks and should be aware of both - but I tryed that anyway) and still I get no reply back from the GATEWAY.

So my question is this

Does the 1841 router treats F0/0 as the WAN link and F0/1 as the LAN link as it is in the normal TPLINK  home router and this is why the traffic cannot get past the router?

 

[Richard Burts]

You ask this question "Does the 1841 router treats F0/0 as the WAN link and F0/1 as the LAN link "  The answer is that no the 1841 router does not necessarily treat any interface particularly as WAN or as LAN. The decision about which interface is WAN and which interface is LAN depends on the IP addresses assigned and the routing configured.

We do not have much detail to work with about this issue. Based on the little that we do know I would guess that the issue is that your Gateway does not know about the 10.90.0.0 network. One potential solution to this would be to configure the Gateway with a route for the 10.90.0.0 network.

But that might not be the best solution. For your PC to access the Internet its private address would need to be translated to some public address. One option might be to configure your Gateway to translate the 10.90.0.0 network. But the other solution might be for you to configure address translation on the 1841 so that packets from the PC arrive at the Gateway with an address in 192.168.1.0.

HTH

Rick

[silviu1983]

Thanks for the replies.

I eventually managed to figure out why the packets didnt go back and the answer downed on me that my cheap home router didnt have a way to put a static route that would notify about the 10 network that sits after the 1841 router, and i am guessing that the home router (gateway in my lan) would send the packets to wan (actually internet link)

however i ran into another problem if anybody is inclined to help me

i removed my home router and i put my 1841 router in its place so the network configuration is like this

1841 - pc

that simple

on my 1841 router i have 2 interfaces

f0/0  - 94.x.x.x - this is my actual external internet ip address

f0/1 - 192.168.0.1

i erased the startup-config so i could start fresh

and the only thing i configured is this

int f0/0 94.x.x.x  255.255.255.240

mac-address x.x.x.x

no shut

int f0/1 192.168.0.1 255.255.255.0

no shut

ip nat pool silviu 94.x.x.x  94.x.x.x(same IP) netmask 255.255.255.240

ip nat inside source list 1 pool silviu  overload

int f0/1

ip nat inside

intf0/0

ip nat outside

access-list 1 permit 192.168.0.0  0.0.0.255

ip route 0.0.0.0  0.0.0.0  94.X.X.X

ip name-server MYDNSSERVER

I configured my pc 

192.168.0.2

255.255.255.0

gw 192.168.0.1

dns 192.168.0.1

and it works , believe it or not, i get connectivity from my PC, I can get to the internet and so on

however

with my home router i get normal speed 10MB /s 

with 1841 router i get 10KB /s maximum, and not to mention that there are times when it does not work

so the question i am asking is this

could this be a faulty router ? ( i have bought it for testing purposes for my CCNA exam, used from a dealer)

or am I doing something wrong?

[Georg Pauwen]

Hello, 

10Kbps could be an MTU issue. Can you post the full running config (show run) of the router ?

[silviu1983]

how can i export it without having to type it manually?

[Georg Pauwen]

Can't you just copy and paste from the command line ?

[silviu1983]

Router#sh run

Building configuration...

Current configuration : 1235 bytes

!

version 12.4

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname Router

!

boot-start-marker

boot-end-marker

!

enable secret 5 $1$OHrS$I8QphSx1bvV0qCqaM4AJY1

!

no aaa new-model

dot11 syslog

ip cef

!

!

!

!

ip name-server 188.x.x.x

ip name-server 94.x.x.x

!

multilink bundle-name authenticated

!

!

!

!

archive

 log config

  hidekeys

!

!

!

!

!

!

!

interface FastEthernet0/0

 mac-address x.x.x

 ip address 94.x.x.x 255.255.255.240

 ip nat outside

 ip virtual-reassembly

 duplex auto

 speed auto

!

interface FastEthernet0/1

 ip address 192.168.0.1 255.255.255.0

 ip nat inside

 ip virtual-reassembly

 duplex auto

 speed auto

!

ip default-gateway 94.x.x.x

ip forward-protocol nd

ip route 0.0.0.0 0.0.0.0 FastEthernet0/0

ip route 0.0.0.0 0.0.0.0 94.x.x.x

!

!

ip http server

no ip http secure-server

ip dns server

ip nat pool silviu 94.x.x.x  94.x.x.x netmask 255.255.255.240

ip nat inside source list 1 pool silviu overload

!

access-list 1 permit 192.168.0.0 0.0.0.255

!

!

!

!

!

!

control-plane

!

!

!

line con 0

 logging synchronous

line aux 0

line vty 0

 password silviu

 login

line vty 1 4

 login

!

scheduler allocate 20000 1000

end

Router#

[Georg Pauwen · Accepted solution]

Make the following changes (marked in bold) to your configuration:

interface FastEthernet0/0
--> no mac-address x.x.x
ip address 94.x.x.x 255.255.255.240
ip nat outside
--> no ip virtual-reassembly
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.0.1 255.255.255.0
ip nat inside
--> no ip virtual-reassembly
duplex auto
speed auto
!
--> no ip default-gateway 94.x.x.x
ip forward-protocol nd
--> no ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
ip route 0.0.0.0 0.0.0.0 94.x.x.x
!
ip http server
no ip http secure-server
ip dns server
!
--> no ip nat pool silviu 94.x.x.x 94.x.x.x netmask 255.255.255.240
ip nat inside source list 1 interface FastEthernet0/0

!
access-list 1 permit 192.168.0.0 0.0.0.255

[silviu1983]

--> no ip nat pool silviu 94.x.x.x 94.x.x.x netmask 255.255.255.240
ip nat inside source list 1 interface FastEthernet0/0


do i disable the fist line or both?

[Georg Pauwen]

Just the first...try the NAT without a NAT pool...

[silviu1983]

so, in a nut shell, it worked :)

could have been the mac-address comand or ip virtual reassembly that was causing the router to slow down?

anyway , thank you for your advice and your time 

cheers

[Georg Pauwen]

The virtual reassembly enabled could really slow everything down, so that was most likely the underlying problem...

[silviu1983]

it was on by default , i didn't put it here.

is it a good practice, when configuring a cisco router to disable it?

[Georg Pauwen]

Hello,

I think it is enabled by default when you configure 'ip nat inside'. Actually, what happens if you turn it back on ? There were some other things in your configuration that could have caused the slowness...

[silviu1983]

so, i turned 

ip virtual-reassembly

on

and i still get the same speed 10MB /s which is great so I am thinking that the slowness came from mac-address, which btw it took me 30 minuets to figure out that cisco router interface will stop working if detects 2 same mac addreses :) on the same lan , or so it was in my case

anyway 

thank you again