Toastboy’s Tech Tips

Cisco 91 / 831 Multi Nat With Public Addresses

Got 5 or more static ips from your bandwidth provider and don’t know how to utilize them all?

If you are like me, and have a cable or dsl connection and were given 5 ips with most home routers you can really only use one of them on the wan side. This was not sufficient for my use. So I found a reasonably price router that could handle having all 5 ips assigned on the front of the router, and I NAT / PAT all of them to different servers / services on my private internal network. Now I can have multiple webservers, DNS servers, Mail Servers all behind my firewall utilizing the 5 public ips assigned to me.

Cisco to the rescue.

Lets setup your Cisco Soho 91 series router for multiple public ip addresses for multi natting / patting to private network servers / workstations.

### Assign a password to your router
Router> enable password <password>

////////////////////////////////////////////////////////////////////
### config ethernet1 (outside) interface with first ip address
### from dsl/cable provider

# get into the enabled exec mode
Router> enable
# enter your password

# config mode
Router# config terminal

# config the outside (public) interface
Router(config)# interface Ethernet1

# assign the first of your ip addresses to the interface
Router(config-if)# ip address <your.public.ip.address> <your.netmask>

# bring up the interface
Router(config-if)# no shutdown

# activate the changes
Router(config-if)# crtl-z
////////////////////////////////////////////////////////////////////

### config the default gateway

Router> enable
Router# conf t
Router(config)# ip default-gateway <your.gateway>
Router(config)# ctrl -z

///////////////////////////////////////////////////////////////////

### config the primary nameservers

Router> enable
Router# conf t
Router(config)# ip name-server <your.default.nameserver.ip.address>
Router(config)# ctrl -z

///////////////////////////////////////////////////////////////////

### enable routing

Router> enable
Router# conf t
Router(config)# ip route 0.0.0.0 0.0.0.0 <your.default.gateway.ip.address>
Router(contif)# ctrl-z

///////////////////////////////////////////////////////////////////

### at this point the router should have access to the internet
### test this connectivity by pinging something past your router

Router> ping google.com

///////////////////////////////////////////////////////////////////

### now setup the inside (LAN) interface
### we are using the private network 10.10.10.0/24

Router> enable
Router# conf t
Router(config)# interface Ethernet0
Router(config-if)# ip address 10.10.10.1 255.255.255.0
Router(config-if)# ctrl-z

///////////////////////////////////////////////////////////////////

### add nat to the interfaces

### add nat to the outside interface
Router> enable
Router# conf t
Router(config)# interface Ethernet1
Router(config-if)# ip nat outside
Router(config-if)# ctrl-z

### add nat to the inside interface
Router> enable
Router# conf t
Router(config)# interface Ethernet
Router(config-if)# ip nat inside
Router(config-if)# ctrl-z

////////////////////////////////////////////////////////////////////

### add the static routes for the local and outside network
Router> enable
Router# conf t
Router(config)# ip route <your.dhcp.network> <your.default.gateway.ip.address> <your.ip.address>
Router(config)# ip route 10.10.10.0 255.255.255.0 10.10.10.1
Router(config)# ctrl-z

Stay tuned for Part 2

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