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Any one can explain asa static nat question ?
Posted on 2014-04-28
Expert, Can you answer the question for me ? I found a configuration in ASA 5520(ver 8.2). The firewall configuration just has one outside
interface ip address, and it has several static nat configuration. In its configuration static (inside,outside), the "outside" ip address
is different from the ASA physical outside interface ip address network.
For example:
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 1.1.1.1 255.255.255.0
static (inside,outside) 2.2.2.2 10.1.1.1
The ip address 1.1.1.1 and 2.2.2.2 are in different net, how can it work ?
Thank you
interface ip address, and it has several static nat configuration. In its configuration static (inside,outside), the "outside" ip address
is different from the ASA physical outside interface ip address network.
For example:
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 1.1.1.1 255.255.255.0
static (inside,outside) 2.2.2.2 10.1.1.1
The ip address 1.1.1.1 and 2.2.2.2 are in different net, how can it work ?
Thank you
[X]
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10 Comments
Active today
>> is different from the ASA physical outside interface ip address network
Yes
Before version 8.3 the command looked like
static (inside,outside) {outside ip address} {inside ip address}netmask {the netmask}
Yes
Before version 8.3 the command looked like
static (inside,outside) {outside ip address} {inside ip address}netmask {the netmask}
Typically you are assigned multiple IP addresses from your ISP.
For instance:
12.34.56.0/29
The ISP router we will assume is 12.34.56.1
Your firewall we will assume is 12.34.56.2
This would give you four usable IPs
12.34.56.3
12.34.56.4
12.34.56.5
12.34.56.6
Most people only have one device on the internet and everything is behind the firewall.
Now assume that you have a web server on 192.168.1.80
You create a static NAT
static (inside,outside) 12.34.56.3 192.168.1.80 netmask 255.255.255.255
This now makes IP 12.34.56.3 exposed to the internet and redirects all traffic from this public IP to it's internal IP.
A firewall rule "ACL" is required to control access to this server
For instance:
12.34.56.0/29
The ISP router we will assume is 12.34.56.1
Your firewall we will assume is 12.34.56.2
This would give you four usable IPs
12.34.56.3
12.34.56.4
12.34.56.5
12.34.56.6
Most people only have one device on the internet and everything is behind the firewall.
Now assume that you have a web server on 192.168.1.80
You create a static NAT
static (inside,outside) 12.34.56.3 192.168.1.80 netmask 255.255.255.255
This now makes IP 12.34.56.3 exposed to the internet and redirects all traffic from this public IP to it's internal IP.
A firewall rule "ACL" is required to control access to this server
Active today
e.g (pre 8.3)
global (outside) 1 interface <-The outside IP is the one on the interface
nat (inside) 1 0.0.0.0 0.0.0.0
interface Vlan2
nameif outside
security-level 0
ip address 123.123.123.123 255.255.255.248 <-This one!
But we can also have a static NAT
static (inside,outside) 123.123.123.124 192.168.1.10 netmask 255.255.255.0
So both 123.123.123.123 and 123.123.123.124 are reachable from outside.
Pete
global (outside) 1 interface <-The outside IP is the one on the interface
nat (inside) 1 0.0.0.0 0.0.0.0
interface Vlan2
nameif outside
security-level 0
ip address 123.123.123.123 255.255.255.248 <-This one!
But we can also have a static NAT
static (inside,outside) 123.123.123.124 192.168.1.10 netmask 255.255.255.0
So both 123.123.123.123 and 123.123.123.124 are reachable from outside.
Pete
Active today
For static NAT after version 8.3 see
Add a Static (One to One) NAT Translation to a Cisco ASA 5500 Firewall
Pete
Add a Static (One to One) NAT Translation to a Cisco ASA 5500 Firewall
Pete
Thank you for your fast reply.
interface Vlan2but 123.123.123.123, and 123.123.123.124 are same ip address net. If they are in different net, for example 1.1.1.1 is its physical ip address and 222.222.222.222 is static outside ip address. Even if it can work, how does its routing work well ?
nameif outside
security-level 0
ip address 123.123.123.123 255.255.255.248 <-This one!
But we can also have a static NAT
static (inside,outside) 123.123.123.124 192.168.1.10 netmask 255.255.255.0
So both 123.123.123.123 and 123.123.123.124 are reachable from outside.
This is possible. I've seen configurations where the firewall has an IP address in a small subnet, for example 1.1.1.0/30. Here the firewall has IP 1.1.1.1 and the ISP router (the firewalls' default gateway) has 1.1.1.2. Now, this subnet is completely used.
If one would like an additional range, like 2.2.2.0/28 (so 14 extra addresses), this can be arranged by letting the ISP router route this subnet through the IP of the firewall. So the ISP has to make arrangements for that.
Once in place, the 2.2.2.0/28 subnet can be 'catched' by the firewall by means of the statics as stated in the original question.
If one would like an additional range, like 2.2.2.0/28 (so 14 extra addresses), this can be arranged by letting the ISP router route this subnet through the IP of the firewall. So the ISP has to make arrangements for that.
Once in place, the 2.2.2.0/28 subnet can be 'catched' by the firewall by means of the statics as stated in the original question.
To Ernie, you are right. But i do not know how the subnet 2.2.2.0/28 route out ? i think if client firewall has the additional ip address(2.2.2.0/28), ISP router must has 2.2.2.0/28 for it, do you think so ? Thank you.
Not sure if I understand your question, but I'll try to give an answer.
The ISP router has a route to the 2.2.2.0/28 network, because the ISP put that in. Something like:
ip route 2.2.2.0 255.255.255.240 1.1.1.1 = forward the packets destined for the 2.2.2.0/28 network to 1.1.1.1. The router knows how to get to 1.1.1.1, because that is a directly attached network.
The ISP router has a route to the 2.2.2.0/28 network, because the ISP put that in. Something like:
ip route 2.2.2.0 255.255.255.240 1.1.1.1 = forward the packets destined for the 2.2.2.0/28 network to 1.1.1.1. The router knows how to get to 1.1.1.1, because that is a directly attached network.
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