Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

cisco 1841 using subinterface to ISP (DHCP)

I am going to replace my home router with a Cisco 1841. But before I do that, I want to configure it so it will work "out of the box".


I will get 2 public IPs from my ISP, and I connect with a LAN cable to the router.


It is my understanding that I could connect ONE cable from the ISP to the FastEthernet 0/0 physical port while having TWO subinterface created on that physical interface?


so it will be:

FastEthernet 0/0.1

ip address dhcp


FastEthernet 0/0.2

ip address dhcp


What else do I need to configure in order to make it work?

Do I have to put those two interfaces in the same VLAN or in different? currently I've put them in vlan 5 and 6.


Behind the 1841 I will put a 2960 switch so I will be working with a couple of VLANs as well.


Any suggestions or just pointing me in the right direction are welcome.

Everyone's tags (1)

Hi ,  Answer me below

Hi , 

 Answer me below question 

1) How Many ISP you are going to connect ??

2) share me show version of router . 

3) How many user VLAN behind your router ?? 





New Member

Hi, Thanks for taking the



Thanks for taking the time to help out.


1) I am connecting to one ISP, and they give me 2 IPs.


Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.4(22)YB8, RELEASE SOFTWARE (fc1)
Technical Support:
Copyright (c) 1986-2010 by Cisco Systems, Inc.
Compiled Fri 22-Oct-10 17:07 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)

max uptime is 7 hours, 22 minutes
System returned to ROM by power-on
System image file is "flash:c1841-ipbase-mz.124-22.YB8.bin"

Cisco 1841 (revision 7.0) with 115712K/15360K bytes of memory.
Processor board ID FCZ122960N4
2 FastEthernet interfaces
1 terminal line
1 Cellular interface
DRAM configuration is 64 bits wide with parity disabled.
191K bytes of NVRAM.
31360K bytes of ATA CompactFlash (Read/Write)

Configuration register is 0x2102


I've ordered new dram and new flash to be able to update to v15.4


3) There will be a total of 8 VLAN (including native, not using vlan 1).



CreatePlease to create content