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Beginner

can I pass vlans from one FE port on a Cisco 1841 to the other FE port

due to upcoming changes to our network I'd like to be able to pass vlans across the FE ports of a Cisco 1841 router.

1 port would go to a managed switch and then to local devices on different VLANs.

the 2nd port would go upstream to a Cisco 3825 at a different location which would then connect to the internet.

due to monitoring behind the Cisco3825 we would like all NAT to occur on the 3825.

what I would like to happen is this

example

device connected to port 7 on managed switch gets an IP (10.0.7.10) from the Cisco 1841 in VLAN 7 (10.0.7.0/24).

traffic from that device goes to the switch, then in f0/1 on the 1841 and out f0/0 still with the same IP info, no NAT occuring.

traffic is received on the 3825 port 0/1 and then NAT occurs and out port 0/0 to the internet.

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Advisor

can I pass vlans from one FE port on a Cisco 1841 to the other F

If I understand the OP correctly, then yes, any nat configuration on the 1841 would need to be removed. The default route on the 1841 could point to the 3825, and the 3825 would have nat configured on it. In this configuration though, a routing protocol would be recommended because since nat isn't used until it hits the 3825, the 3825 will need to know how to get back to every network behind the 1841.

HTH,

John

HTH, John *** Please rate all useful posts ***
4 REPLIES 4
Advisor

can I pass vlans from one FE port on a Cisco 1841 to the other F

Michael,

I honestly do better with pictures , but it sounds like this is a basic setup. Is below what you have:

host ---> switch ---> (fa0/1) 1841 (fa0/0) ----> fa0/1 3825 ---> Internet?

If so, is your switch l3 or will you be doing vlans on the 1841? NAT can occur on the 3825 and you don't have to nat on the 1841.

HTH,

John

HTH, John *** Please rate all useful posts ***
Frequent Contributor

can I pass vlans from one FE port on a Cisco 1841 to the other F

John just to confim for my understanding on the 1841 if he has "nat inside, nat outside" statements under his interfaces he will have to remove them correct?

Advisor

can I pass vlans from one FE port on a Cisco 1841 to the other F

If I understand the OP correctly, then yes, any nat configuration on the 1841 would need to be removed. The default route on the 1841 could point to the 3825, and the 3825 would have nat configured on it. In this configuration though, a routing protocol would be recommended because since nat isn't used until it hits the 3825, the 3825 will need to know how to get back to every network behind the 1841.

HTH,

John

HTH, John *** Please rate all useful posts ***
Beginner

can I pass vlans from one FE port on a Cisco 1841 to the other F

Setting up RIP ver 2 on both routers fixed the problem.  Thanks

Mike

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