Cisco Systems Inside to Inside NAT

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Subject Author Date
Inside to Inside NAT Jonathan Wright 04-11-07
Posted by Jonathan Wright on April 11, 2007, 5:08 pm
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I'm trying to configure my c837 to use inside-to-inside NAT, but I'm not
getting anywhere, and everywhere I've looked on the Internet regarding
this problem seams to tail off without resolve...

Basically, I'm trying to access my internal web server using the global
IP address assigned to Dialer0 on the router by my ISP.

I have a DNS service external to the network which is provided this IP
address and while I can use it externally (PAT from the Internet to the
LAN is working fine), I can't get it to work when I'm on the network.

In this case, internal replication of the DNS zone on the LAN is not
really an option, and for the moment, I'm using a hosts file (but again,
this isn't suitable, as some devices will need to access it both on and
off the network).

I'm just looking to get Inside-to-Inside NAT working so I can use the
router to forward the request from the LAN to the server...

Here's the main points of my config:

interface Ethernet0
description to Network
ip address 10.0.1.62 255.255.255.192
ip access-group from-network in
no ip redirects
no ip unreachables
no ip proxy-arp
ip nat inside
no ip virtual-reassembly
ip route-cache flow
load-interval 30
!
interface ATM0
description to Zen Internet
no ip address
no ip redirects
no ip unreachables
no ip proxy-arp
no atm ilmi-keepalive
dsl operating-mode auto
pvc 0/38
description BT ADSL Connection
tx-ring-limit 3
encapsulation aal5mux ppp dialer
dialer pool-member 1
!
interface Dialer0
ip address negotiated
ip access-group from-internet in
no ip redirects
no ip unreachables
no ip proxy-arp
ip nat outside
ip inspect firewall out
no ip virtual-reassembly
encapsulation ppp
ip route-cache flow
load-interval 30
dialer pool 1
dialer-group 1
!
ip route 0.0.0.0 0.0.0.0 Dialer0
!
ip nat inside source list nat interface Dialer0 overload
ip nat inside source static tcp 10.0.1.61 80 interface Dialer0 80
!
ip access-list standard nat
remark Define which systems will be NAT-translated
permit 10.0.1.0 0.0.0.63
!
ip access-list extended from-internet
remark ACL for incoming traffic from the Internet
deny ip 10.0.0.0 0.255.255.255 any
deny ip 172.16.0.0 0.15.255.255 any
deny ip 192.168.0.0 0.0.255.255 any
deny ip 127.0.0.0 0.255.255.255 any
deny ip host 255.255.255.255 any
deny ip host 0.0.0.0 any
permit icmp any any echo-reply
permit icmp any any time-exceeded
permit icmp any any unreachable
permit igmp any any
permit esp any any
permit gre any any
permit udp any eq ntp any eq ntp
permit tcp any any eq www
deny ip any any log
ip access-list extended from-network
remark ACL for incoming traffic to the router from the network
deny ip host 255.255.255.255 any
deny ip 127.0.0.0 0.255.255.255 any
permit ip any any
!
dialer-list 1 protocol ip permit

--
Jonathan Wright mail@djnauk.co.uk
http://djnauk.co.uk

cat /dev/random (you never know, you may see something you like!)

2.6.17-gentoo-r3-djnauk-b1 AMD Athlon(tm) XP 2100+
up 9 days, 23:47, 1 user, load average: 0.24, 0.41, 0.61

Posted by Thrill5 on April 13, 2007, 6:20 pm
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You can't do inside to inside NAT. NAT is only done inside to outside and
vice versa. By configuring interfaces as either "inside" or "outside" is
how the router knows which packets to NAT.

Scott

> I'm trying to configure my c837 to use inside-to-inside NAT, but I'm not
> getting anywhere, and everywhere I've looked on the Internet regarding
> this problem seams to tail off without resolve...
>
> Basically, I'm trying to access my internal web server using the global IP
> address assigned to Dialer0 on the router by my ISP.
>
> I have a DNS service external to the network which is provided this IP
> address and while I can use it externally (PAT from the Internet to the
> LAN is working fine), I can't get it to work when I'm on the network.
>
> In this case, internal replication of the DNS zone on the LAN is not
> really an option, and for the moment, I'm using a hosts file (but again,
> this isn't suitable, as some devices will need to access it both on and
> off the network).
>
> I'm just looking to get Inside-to-Inside NAT working so I can use the
> router to forward the request from the LAN to the server...
>
> Here's the main points of my config:
>
> interface Ethernet0
> description to Network
> ip address 10.0.1.62 255.255.255.192
> ip access-group from-network in
> no ip redirects
> no ip unreachables
> no ip proxy-arp
> ip nat inside
> no ip virtual-reassembly
> ip route-cache flow
> load-interval 30
> !
> interface ATM0
> description to Zen Internet
> no ip address
> no ip redirects
> no ip unreachables
> no ip proxy-arp
> no atm ilmi-keepalive
> dsl operating-mode auto
> pvc 0/38
> description BT ADSL Connection
> tx-ring-limit 3
> encapsulation aal5mux ppp dialer
> dialer pool-member 1
> !
> interface Dialer0
> ip address negotiated
> ip access-group from-internet in
> no ip redirects
> no ip unreachables
> no ip proxy-arp
> ip nat outside
> ip inspect firewall out
> no ip virtual-reassembly
> encapsulation ppp
> ip route-cache flow
> load-interval 30
> dialer pool 1
> dialer-group 1
> !
> ip route 0.0.0.0 0.0.0.0 Dialer0
> !
> ip nat inside source list nat interface Dialer0 overload
> ip nat inside source static tcp 10.0.1.61 80 interface Dialer0 80
> !
> ip access-list standard nat
> remark Define which systems will be NAT-translated
> permit 10.0.1.0 0.0.0.63
> !
> ip access-list extended from-internet
> remark ACL for incoming traffic from the Internet
> deny ip 10.0.0.0 0.255.255.255 any
> deny ip 172.16.0.0 0.15.255.255 any
> deny ip 192.168.0.0 0.0.255.255 any
> deny ip 127.0.0.0 0.255.255.255 any
> deny ip host 255.255.255.255 any
> deny ip host 0.0.0.0 any
> permit icmp any any echo-reply
> permit icmp any any time-exceeded
> permit icmp any any unreachable
> permit igmp any any
> permit esp any any
> permit gre any any
> permit udp any eq ntp any eq ntp
> permit tcp any any eq www
> deny ip any any log
> ip access-list extended from-network
> remark ACL for incoming traffic to the router from the network
> deny ip host 255.255.255.255 any
> deny ip 127.0.0.0 0.255.255.255 any
> permit ip any any
> !
> dialer-list 1 protocol ip permit
>
> --
> Jonathan Wright mail@djnauk.co.uk
> http://djnauk.co.uk
>
> cat /dev/random (you never know, you may see something you like!)
>
> 2.6.17-gentoo-r3-djnauk-b1 AMD Athlon(tm) XP 2100+
> up 9 days, 23:47, 1 user, load average: 0.24, 0.41, 0.61



Posted by Rod Dorman on April 16, 2007, 12:58 pm
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>You can't do inside to inside NAT. NAT is only done inside to outside and
>vice versa. By configuring interfaces as either "inside" or "outside" is
>how the router knows which packets to NAT.

It could be he's thinking that inside/outside interfaces are somehow
related with private/public IP addresses.

--
                                        -- Rod --
rodd(at)polylogics(dot)com

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