Basic Interface Configuration of Cisco ASA 5520
The Cisco ASA 5520 is one of the mid-range ASAs. 4 Gigabit Ethernet ports. Max 450 Mbps throughput under ideal conditions. Good for mid-sized offices. Has an expansion slot where you can install an add-on card that does content filtering (e.g. email and web) or intrusion prevention. Or you can install an expansion card that gives your ASA more physical ports.
The lowest-end ASA is the Cisco ASA 5505 model, which is a more like a switch with VLANs. But on the 5510 models and up, interface config is akin to that of a router.
Factory Default Settings on the ASA 5520
Out of the box, or with the configure factory-default command, the ASA 5520 is configured thusly:
Interface | Name | Security Level | IP Address | State |
GigabitEthernet0/0 | no nameif | no security-level | no ip address | Shutdown |
Management0/0 | management | 100 | 192.168.1.1 | Management-only |
Configuration Example
On a Cisco ASA 5520 with a factory default config, a show run interface coughs up this information:
interface GigabitEthernet0/0
shutdown
no nameif
no security-level
no ip address
!
interface GigabitEthernet0/1
shutdown
no nameif
no security-level
no ip address
!
interface GigabitEthernet0/2
shutdown
no nameif
no security-level
no ip address
!
interface GigabitEthernet0/3
shutdown
no nameif
no security-level
no ip address
!
interface Management0/0
nameif management
security-level 100
ip address 192.168.1.1 255.255.255.0
management-only
With nothing configured on the interfaces, the routing table on a factory default ASA shows only the loopback interface:
ciscoasa(config-if)# show route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C 127.0.0.0 255.255.0.0 is directly connected, cplane
To make an interface operational, it needs a name, an IP address, a security level and it needs to be administratively brought up with the no shutdown command.
So let’s give the GigabitEthernet0/0 interface a name and an IP address.
ciscoasa# con t
ciscoasa(config)# interface gigabitEthernet 0/0
ciscoasa(config-if)# nameif outside
INFO: Security level for "outside" set to 0 by default.
ciscoasa(config-if)# ip address 5.5.5.1
When an interface is named “outside”, the ASA automatically assigns the interface a security level of 0. If an interface is named “inside”, it is automatically given a security level of 100.
To view the config on all interfaces, use the show run interface command. To view just one interface, use theshow run interface command and specify the interface:
ciscoasa(config-if)# sh ru int g 0/0
!
interface GigabitEthernet0/0
shutdown
nameif outside
security-level 0
ip address 5.5.5.1 255.0.0.0
Because I did not specify a subnet mask when I configured the IP address, the interface was automatically assigned a classful subnet mask. I can specify the subnet mask in the ip address command.
ciscoasa(config-if)# ip address 5.5.5.1 255.255.255.0
ciscoasa(config-if)# sh ru int g 0/0
!
interface GigabitEthernet0/0
shutdown
nameif outside
security-level 0
ip address 5.5.5.1 255.255.255.0
When I am ready to bring the interface up, I use the no shutdown command.
ciscoasa(config-if)# no shut
ciscoasa(config-if)# sh ru int g 0/0
!
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 5.5.5.1 255.255.255.0
The show run ip address command shows all interfaces that have IP addresses.
ciscoasa(config-if)# sh ru ip
!
interface GigabitEthernet0/0
nameif outside
security-level 0
ip address 5.5.5.1 255.255.255.0
!
interface Management0/0
nameif management
security-level 100
ip address 192.168.1.1 255.255.255.0
The show ip address command also displays all IP addresses, along with the method used to configure the IP address. (“System IP Addresses” refer to the primary IP addresses used for failover. “Current IP Addresses” are the currently-used IP addresses on the interface(s). So, in an active/standby ASA pair, the active ASA would have the same “System” and “Current” IP addresses. The standby ASA would have different “System” and “Current” IP addresses.)
ciscoasa(config-if)# sh ip
System IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 manual
Management0/0 management 192.168.1.1 255.255.255.0 manual
Current IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 manual
Management0/0 management 192.168.1.1 255.255.255.0 manual
After a write memory and a reload, when you do show ip address, the “Method” on these manually-configured interfaces changes to CONFIG, signifying that they were loaded from the startup config:
ciscoasa# sh ip
System IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 CONFIG
Management0/0 management 192.168.1.1 255.255.255.0 CONFIG
Current IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 CONFIG
Management0/0 management 192.168.1.1 255.255.255.0 CONFIG
Now a show route command displays the directly-connected route to the 5.5.5.0 subnet.
ciscoasa(config-if)# sh ro
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C 5.5.5.0 255.255.255.0 is directly connected, outside
C 127.0.0.0 255.255.0.0 is directly connected, cplane
From the show run interface command, we can see that there is nothing configured on the g 0/1 interface. Let’s set it as a DHCP client and bring it up.
ciscoasa(config-if)# sh ru int g 0/1
!
interface GigabitEthernet0/1
shutdown
no nameif
no security-level
no ip address
ciscoasa(config-if)# nameif inside
INFO: Security level for "inside" set to 100 by default.
ciscoasa(config-if)# ip add dhcp
ciscoasa(config-if)# no shut
The show run interface command will show that g 0/1 is a DHCP client, but it will not display the dynamically-assigned IP address on the interface. To view the DHCP IP address, use the show ip address command.
ciscoasa(config-if)# sh ip add
System IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 CONFIG
GigabitEthernet0/1 inside 10.30.1.101 255.255.255.0 DHCP
Management0/0 management 192.168.1.1 255.255.255.0 CONFIG
Current IP Addresses:
Interface Name IP address Subnet mask Method
GigabitEthernet0/0 outside 5.5.5.1 255.255.255.0 CONFIG
GigabitEthernet0/1 inside 10.30.1.101 255.255.255.0 DHCP
Management0/0 management 192.168.1.1 255.255.255.0 CONFIG
Note that the “Method” for g 0/1 is “DHCP”.
You can also display all IP addresses on all interfaces with the show interface ip brief command.
ciscoasa(config-if)# sh int ip b
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 5.5.5.1 YES CONFIG up up
GigabitEthernet0/1 10.30.1.101 YES DHCP up up
GigabitEthernet0/2 unassigned YES unset administratively down down
GigabitEthernet0/3 unassigned YES unset administratively down down
Internal-Control0/0 127.0.1.1 YES unset up up
Internal-Data0/0 unassigned YES unset up up
Management0/0 192.168.1.1 YES CONFIG down down
Virtual254 unassigned YES unset up up
More Related Cisco ASA Tips:
Cisco ASA 5520 Basic Configuration Guide
Site-to-Site IPSEC VPN between Two Cisco ASA 5520
How to Configure Dual ISP on Cisco ASA 5505?
Cisco ASA 8.4 vs. Typical NAT/PAT Configuration
Eight Commands on a Cisco ASA Security Appliance You Should Know
VLAN Sub-Interfaces on Cisco ASA 5500 Firewall Configuration