Cisco 3620 Sub Interfaces / NAT

Posted on 2004-03-28
Last Modified: 2008-03-10
I am looking for some assistance in creating some
sub Interfaces and NAT on a CISCO 3620.

Here is what I am looking at doing.

Int 0/0.1  - /25 (NO Nat)
Int 0/0.2  -   /23 (NAT Masquerade)
Int 0/0.3  -   /24 (NAT Masquerade)
Serial 0/0 - /30

Default Route to (via Serial 0/0)

I want Each Sub-Interface to be able to route to
the other sub interfaces and all to route to a the
internet via Serial 0/0 (T1 CSU/DSU).

I am running Cisco IOS ver 12.1(5)  and will be upgrading
to '12.3(5)' in the next couple of days.

Thanks for any help.

Mark Anderson

Question by:networkfrontier
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LVL 79

Accepted Solution

lrmoore earned 500 total points
ID: 10700461
That's pretty easy if you want to nat  everything to the serial 0/0 interface address

interface serial 0/0
 ip nat outside
interface ethernet 0/0.1
 ip address

interface ethernet 0/0.2
 ip address
 ip nat inside
interface ethernet 0/0.3
 ip address
 ip nat inside
access-list 2 permit
access-list 2 permit
ip nat inside source list 2 interface serial0/0 overload

That's about all you have to do for simple nat


Author Comment

ID: 10728261

When I try this  I get :

% 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.

How do I get around this?

Mark Anderson
LVL 79

Expert Comment

ID: 10728546
Assuming that your switch is using dot1Q vlan tagging:

interface ethernet 0/0.2
 encapsulation dot1Q 2  <-- VLAN #
 ip address

interface ethernet 0/0.3
 encapsulation dot1Q 3  <-- VLAN #
 ip address

I was not sure if you were doing VLAN Ethernet sub-interfaces or serial sub-interfaces like on a frame-relay wan..


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