4 DHCP IP's from ISP to 4 VLANS ?

[Didier1966]

Hello,

Just for training purpose in my lab , I would like to know if it is possible to receive 4 IP addresses on 1 INTERFACE ?

To be more clear :

My ISP allow and give me 4 IP addresses from a DHCP POOL, at the moment my CISCO 1841 ROUTER only use one , for most of the cases it is OK , but I was wondering how I could use :

DHCP IP 1 to VLAN 10

DHCP IP 2 to VLAN 20

DHCP IP 3 to VLAN 30

DHCP IP 4 to VLAN 40

In other words :

My ISP arive in

INT FA0/0

and come out in

INT FA0/0/0 

INT FA0/0/1

INT FA0/0/2

INT FA0/0/3

This is what does NOT work :

interface FastEthernet0/0.10

description VLAN 10

encapsulation dot1Q 10

ip address dhcp

ip access-group dri-acl-in in

ip nat outside

ip virtual-reassembly

no cdp enable

!        

interface FastEthernet0/0.20

description VLAN 20

encapsulation dot1Q 20

ip address dhcp

ip access-group dri-acl-in in

ip nat outside

ip virtual-reassembly

no cdp enable

interface FastEthernet0/0.30

description VLAN 30

encapsulation dot1Q 30

ip address dhcp

ip access-group dri-acl-in in

ip nat outside

ip virtual-reassembly

no cdp enable

interface FastEthernet0/0.40

description VLAN 40

encapsulation dot1Q 40

ip address dhcp

ip access-group dri-acl-in in

ip nat outside

ip virtual-reassembly

no cdp enable

interface FastEthernet0/0/0

switchport access vlan 10

spanning-tree portfast

!        

interface FastEthernet0/0/1

switchport access van 20

spanning-tree portfast

!        

interface FastEthernet0/0/2

switchport access van 30

spanning-tree portfast

!        

interface FastEthernet0/0/1

switchport access van 40

spanning-tree portfast

!        

ip nat inside source list NAT interface FastEthernet0/0 overload

ip nat inside source list NAT10 interface FastEthernet0/0.10 overload

ip nat inside source list NAT20 interface FastEthernet0/0.20 overload

ip nat inside source list NAT30 interface FastEthernet0/0.30 overload

ip nat inside source list NAT40 interface FastEthernet0/0.40 overload

THis is just a example how I would like to see it , but I am sure I am completely wrong.

Thank you in advance for your help and hints

Best Regards,

Didier

[Edison Ortiz]

It will work if your ISP also uses subinterfaces.

Here is what I did on my lab

On the ISP side:

ip dhcp excluded-address 1.1.1.1
ip dhcp excluded-address 2.2.2.1
ip dhcp excluded-address 3.3.3.1
!        
ip dhcp pool CISCO
   network 1.1.1.0 255.255.255.0
   domain-name CISCO.COM
   default-router 1.1.1.1
!
ip dhcp pool CISCO2
   network 2.2.2.0 255.255.255.0
   domain-name CISCO2.COM
   default-router 2.2.2.1
!
ip dhcp pool CISCO3
   network 3.3.3.0 255.255.255.0
   domain-name CISCO3.COM
   default-router 3.3.3.1
!
interface GigabitEthernet1/0
no ip address
negotiation auto
!
interface GigabitEthernet1/0.1
encapsulation dot1Q 1 native
ip address 1.1.1.1 255.255.255.0
!
interface GigabitEthernet1/0.2
encapsulation dot1Q 2
ip address 2.2.2.1 255.255.255.0
!
interface GigabitEthernet1/0.3
encapsulation dot1Q 3
ip address 3.3.3.1 255.255.255.0

On the client side:

interface GigabitEthernet1/0
no ip address
negotiation auto
!
interface GigabitEthernet1/0.1
encapsulation dot1Q 1 native
ip address dhcp
!
interface GigabitEthernet1/0.2
encapsulation dot1Q 2
ip address dhcp
!
interface GigabitEthernet1/0.3
encapsulation dot1Q 3
ip address dhcp

Router#sh ip int bri | ex una
Interface                  IP-Address      OK? Method Status                Protocol
GigabitEthernet1/0.1       1.1.1.2         YES DHCP   up                    up     
GigabitEthernet1/0.2       2.2.2.2         YES DHCP   up                    up     
GigabitEthernet1/0.3       3.3.3.2         YES DHCP   up                    up

Another thing, you can't use the Vlan on another interface on the client side.

Since you are NAT out, you can simply create another Vlan and IP subnet with the 'interface vlan' command and NAT that out.

For instance:

interface FastEthernet0/0/0

switchport access vlan 100

spanning-tree portfast

interface vlan 100

ip address 192.168.1.x 255.255.255.0

access-list 1 permit 192.168.1.x

ip nat inside source list 1 interface FastEthernet0/0.10 overload

[Didier1966]

Hello Edison,

Sorry for my late reply

Yes this will work but what I would like to archive is "I think" not possible with the routers that I have (2611 / 2621 / 2650 / 1841).

To be more specific , my ISP can give me 4 IP from their DHCP SERVER.

When I connect computer 1 directly to my ISP , I receive a IP from my ISP and they keep my MAC ADDRESS in memory for 1 Hour

I do this test with a other computer and 2 routers (I do not have 4 computers).

So I know my ISP give me this IP ADDRESSES , the problem is :

If I connect my CISCO 1841 ROUTER to my ISP MODEM , they will only see ONE MAC ADDRESS , so they will give me ONLY ONE IP.

Is their any way to emulate 4 MAC ADDRESSES on one FISCAL CONNECTION ? If this is possible the problem is solved.

THIS IS ONLY FOR TEST AND TRAINING PURPOSES , IT IS NOT URGENT

Best Regards,

Didier

[Edison Ortiz · Accepted solution]

"Is their any way to emulate 4 MAC ADDRESSES on one FISCAL CONNECTION ? If this is possible the problem is solved."

You can connect a switch or a hub to the ISP handoff and this way you can have 4 devices obtaining the DHCP address.

[Didier1966]

Hello Edison,

This I know and this work also , but I would like to do it with one socket or interface.

But again , like every INTERFACE connection , this has only ONE MAC ADDRESS ?!?

Thank you for you help

I will close the case here , I do not ink it is possible , and maybe I will never needed ?!?

Best Regards,

Didier