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Router Config

Posted on 2011-04-29
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Last Modified: 2012-05-11
Hello EE. I have a question on router configuration. We have a T1 circuit provided to us by an ISP. The circuit did not come with a managed router.  I had to get a DSU/CSU T1 card for my cisco 1841 router and configured it with the wan IP info provided to me by the ISP. Everything is working fine.  My question is can I still make use of the Lan block of IPs provided to us by the ISP without another router? I have 2 fastethernet ports but one is in use to connect to the inside network.
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Question by:InSearchOf
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Assisted Solution

by:sshah254
sshah254 earned 664 total points
ID: 35491878
Of course ... your block of IP that is assigned to you comes over the T1.  Feel free to use those IPs and use them (NAT, DMZ, etc.)

Ss
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Soulja earned 668 total points
ID: 35491882
On the other interface, just create subintefaces,i.e. fa0/1.1, fa0/1.2 and assign the appropriate ip scheme to them.
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by:Soulja
ID: 35491912
Im Sorry,

Are the ip blocks LAN or WAN ips? If wan, then sshah254 is correct.
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Author Comment

by:InSearchOf
ID: 35492103
The IP blocks are lan.
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by:Craig Beck
Craig Beck earned 668 total points
ID: 35492160
Configure the IPs on a different interface so you can use them as actual IPs for hosts, or you can NAT or PAT to hosts on your private LAN.
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Author Comment

by:InSearchOf
ID: 35492240
Being that I only have 1 available fastethernet port I would have to use subinterfaces as suggested  by Soulja but there is no connection to that port. How would traffic be passed?
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Expert Comment

by:Soulja
ID: 35492600
My suggestion is based on the assumption that you have several blocks of LAN addresses that you want to assigned default gateways for. The subinterfaces would be gateways for the lan subnets for the purpose of a "router on stick" configuration. If this is not what you are trying to accomplish please expound.
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Author Comment

by:InSearchOf
ID: 35492666
Well, it sounds like what I am interested in I have 1 block of lan addresses consisting of 5 IPs and I would like to make use of them. My only connection to the outside is through the serial interface. If I use a lan IP on one subinterface as a gateway and another IP address on the second subinterface how does traffic pass back and forth without a physical connection to the interface?
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Expert Comment

by:Soulja
ID: 35492776
This sounds like the ISP gave you additional static wan ip address, not Lan address, so as sshah suggested initially, these IP can be used for DMZ host, natting, etc.
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Author Comment

by:InSearchOf
ID: 35492971
No, they gave me a set of single wan IPs that I used to configure my serial interface because they did not provide a router and they also gave me a block 5 lan IPs to use. Here is what they gave me:

WAN IP Information

Wan Default Gateway (ISP)           XXX.XXX.X10.XXX
Customer WAN IP:                         XXX.XXX.X10.XXX
Subnet Mask:                                 XXX.XXX.XXX.XXX

LAN IP Information

Public Lan Network:                       XXX.XXX.X12.XXX
Subnet Mask                                  XXX.XXX.XXX.XXX
Usable Public IPs                            XXX.XXX.X12.XXX - XXX.XXX.X12.XXX

I used the WAN IP Information.
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Expert Comment

by:Soulja
ID: 35493000
Yes, the key word is public. These looks like addresses you could use for a DMZ type of setup.
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Expert Comment

by:Craig Beck
ID: 35494103
The router you have has 2x FastEthernet ports, so you can assign the router address specified in the LAN IP information to the free FastEthernet port.  You will then have 5 IP addresses available for hosts.
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Author Comment

by:InSearchOf
ID: 35494275
Ok. Thanks for the useful posts guys. I guess I would need some kind of route statement to route traffic from public lan IP to the to wan interface whether I went with the DMZ or addressing one of my ethernet ports?
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Author Comment

by:InSearchOf
ID: 35508348
I am trying to configure a sub interface but I am getting this error:

% Configuring IP routing on a LAN subinterface is only allowed if that
subinterface is already configured as part of an IEEE 802.10, IEEE 802.1Q,
or ISL vLAN.
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LVL 26

Expert Comment

by:Soulja
ID: 35513122
This is because you have to apply some type of vlan encapsulation on the interface first.

try encapsulation dot1q x

x being the vlan number you want that interface to route for.
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