Basic Router Question

[it000000103]

I have an 1841 running 15.1 I am trying to do a simple router set up.

I have a real basic router config that I just can figure out.

I have stripped this config down to as much as I can.

The problem I am having is that it is not routing and I cannot see what I am missing.

The set up is as follows

PC ---------------->  Switch ------------> Router1841 Eth0/1 --------à Router1841 Eth0/0 -----------------à RouterISP-------------------à Internet

10.10.10.100       10.10.10.10               10.10.10.1                   DHCP 10.1.10.10                            10.1.10.1

I can ping from the PC to 10.1.10.10 (Eth0/0)

I can ping from Router1841 to the PC

I can ping from the Router1841 to 10.1.10.1 (Router ISP)

I cannot ping from the PC to RouterISP and nothing will go out from Router1841 through RouterISP  (traceroute for example anything)

Router ISP works perfectly when I plug a PC into it and surf the net

I can ping RouterISP using either a straight through ethernet cable or a crossover cable

I have tried both a static  IP address and DHCP on Eth0/0

Can you look through the config and see what I am missing.  It has to be something simple that I just can see

I have tried this with and without dhcp.

!

! Last configuration change at 21:57:53 UTC Wed Sep 11 2013

!

version 15.1

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname IPAT

!

boot-start-marker

boot-end-marker

!

!

enable secret 5 $1$rL95$5ZDg3CHbqb77SIf4cm.6S.

enable password Patt3rns

!

no aaa new-model

dot11 syslog

no ip source-route

!

!

!

!

!

ip cef

multilink bundle-name authenticated

!

crypto pki token default removal timeout 0

!

!

!

!

license udi pid CISCO1841 sn FTX145000RF

!

!

!

!

!

!

interface FastEthernet0/0

description $ES_WAN$

ip address dhcp client-id FastEthernet0/0

speed auto

full-duplex

no mop enabled

!

interface FastEthernet0/1

description $ES_LAN$

ip address 10.10.10.1 255.255.255.0

duplex auto

speed auto

!

interface Serial0/0/0

no ip address

shutdown

!

ip forward-protocol nd

!

ip http server

no ip http secure-server

!

ip route 0.0.0.0 0.0.0.0 FastEthernet0/0

!

logging esm config

!

!

control-plane

!

!

!

line con 0

line aux 0

line vty 0 4

password RVDV11rvdv

login

transport input all

!

scheduler allocate 20000 1000

end

Thanks in advance

[pedram rabeti]

Hi ,

Please run the ' Show Run ' command on 3 router  and write the results here .

[John Blakley]

I'm assuming that the ISP router is doing nat for you. The issue seems to be that the ISP router doesn't know how to get back to the 10.10.10.0 subnet. You can do this one of two ways if that's the case. You can have the ISP add a route to 10.10.10.0 pointing to 10.1.10.10 if you don't have access to the router. If you have access to the router, you'll need to add that route.

If you don't have access to the router, you can always set nat up on the router that leads to the ISP router, but then you're double natting which is doable, just not desirable.

HTH,
John

*** Please rate all useful posts ***

[Richard Burts · Accepted solution]

From the statement that it works fine if the original poster connects a PC instead of the router I agree that the ISP is doing address translation for the address on the Fast0/0 interface. But it sure sounds to me like the ISP does not know about the 10.10.10.0 subnet and is not translating for that subnet. Perhaps the original poster can request that the ISP do translation for that subnet. But I think that it would also work if the original poster would configure address translation to do overload on the Fast0/0 interface.

I also note a possible issue with the default static route which is

ip route 0.0.0.0 0.0.0.0 FastEthernet0/0

When static routes point at an Ethernet interface then it requires that the other router (the ISP) have enabled proxy arp. If the ISP does not support proxy arp (and I believe that an increasing number of them do not) then the static route will not work. It would be much better to use something like this

ip route 0.0.0.0 0.0.0.0 dhcp

HTH

Rick

[it000000103]

That nailed it.

I enabled NAT, which frustrates me to double NAT.

Then I set FastEthernet0/0 to DHCP

Deleted ip route 0.0.0.0 0.0.0.0 FastEthernet0/0

Added ip route 0.0.0.0 0.0.0.0 dhcp

[Richard Burts]

I am glad that our suggestions did lead you to a successful solution for your issue. I understand your frustration at needing to do double NAT. But the alternative would probably be a different level of service from the provider and would probably be more expensive that what you have got.

Thank you for using the rating system to mark this question as answered. It makes the forum more useful when people can read about an issue and can know that a successful solution was found. Your marking has contributed to this process.

HTH

Rick