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Webcast-Catalyst9k
New Member

multiple IPs via DHCP

I have a 876 router that works great with RFC1483 and one IP. I get the IP via DHCP.

This is (some of) my configuration:

interface ATM0

no ip address

no atm ilmi-keepalive

dsl operating-mode auto

!

interface ATM0.1 point-to-point

pvc 8/35

!

bridge-group 1

!
interface BVI1
mac-address 0012.7f8e.8c14
ip address dhcp
ip nat outside
ip virtual-reassembly
---
My ISP has given me 4 more IP's to use, but I can only attain the first one via DHCP. If i had static IP's I would use 'ip address x.x.x.x 255.255.255.252 secondary' - but this isn't possible on DHCP on the same interface.
Do any of you guys have suggestions on how I can bind my 4 other IPs to the router?
I like the NAT-config, and would like to use the other IP's with NAT as well.
bardh

Everyone's tags (5)
7 REPLIES
Purple

Re: multiple IPs via DHCP

You don't need to bind any of these IPs to interfaces to use them with NAT.

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Cisco Employee

Re: multiple IPs via DHCP

Hi,

When your ISP assigns 4 static public addresses to you, you use one address for your router interface and user other 3 IP address for static NAT creation for your servers.

For examples, my ISP gave 4 public IP of 11.1.1.1~11.1.1.4 and my router got 11.1.1.1 from ISP dhcp server.

Then, I will use 11.1.1.2 for my exchange server and 11.1.1.3 for my web server and 11.1.1.4 for FTP server and create static NAT for these 3 addresses so outside world will get to my servers.

Hope this helps.

KK.

New Member

Re: multiple IPs via DHCP

Hi!

Thanks for your reply.

I see what you're saying - but I want all the IPs to be bound to the router. Is that not possible?

How would I go on to create static NAT on the four other IPs?

bardh

Hall of Fame Super Blue

Re: multiple IPs via DHCP

bardh1077 wrote:

Hi!

Thanks for your reply.

I see what you're saying - but I want all the IPs to be bound to the router. Is that not possible?

How would I go on to create static NAT on the four other IPs?

bardh

Bardh

Not sure what you mean by binding. As long as the IPs are routed to you by the ISP which they will be as they have been allocated to you -

internal server = 192.168.5.10

spare public IP = 1.1.1.10

ip nat inside source static 192.168.5.10 1.1.1.10

if you want to use the same public IP for multiple internal servers you can use ports eg.

ip nat inside source static tcp 192.168.5.10 80 1.1.1.10 80

ip nat inside source static tcp 192.168.5.10 443 1.1.1.10 443

etc..

Jon

New Member

Re: multiple IPs via DHCP

Hi Jon

Sorry if I am unclear.

What I mean is, I can't use the IP if it's not leased by DHCP.

I have a pool of 5 IP's, but I can only use 1 at the time on the router (the one "bound" by dhcp).

So the example you gave me doesn't work, because i only have the primary IP leased.

Is there a way to make more than one DHCP request over the same WAN-interface, and in that way making more IPs "usable"?

(Like creating ethernet alias in linux - eth0 for the first ip, eth0:0 for second ip, and so on)

bardh

Cisco Employee

Re: multiple IPs via DHCP

Hi,

Router can't have two ip addresses in same subnet as router is to route pkt for different subnet.

So, it is not possible.

KK.

Hall of Fame Super Blue

Re: multiple IPs via DHCP

bardh1077 wrote:

Hi Jon

Sorry if I am unclear.

What I mean is, I can't use the IP if it's not leased by DHCP.

I have a pool of 5 IP's, but I can only use 1 at the time on the router (the one "bound" by dhcp).

So the example you gave me doesn't work, because i only have the primary IP leased.

Is there a way to make more than one DHCP request over the same WAN-interface, and in that way making more IPs "usable"?

(Like creating ethernet alias in linux - eth0 for the first ip, eth0:0 for second ip, and so on)

bardh

Bardh

Ahhh, i understand. Are those other addresses assigned to your company or are they free to useby other companies ?

You could still use just the one address you get via DHCP by using the port example i gave before.

Jon

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