Use Case: PBF for Outbound Access with Dual ISPs

In this use case, the branch office has a dual ISP configuration and implements PBF for redundant internet access. The backup ISP is the default route for traffic from the client to the web servers. In order to enable redundant internet access without using an internetwork protocol such as BGP, we use PBF with destination interface-based source NAT and static routes, and configure the firewall as follows:

Enable a PBF rule that routes traffic through the primary ISP, and attach a monitoring profile to the rule. The monitoring profile triggers the firewall to use the default route through the backup ISP when the primary ISP is unavailable.
Define Source NAT rules for both the primary and backup ISP that instruct the firewall to use the source IP address associated with the egress interface for the corresponding ISP. This ensures that the outbound traffic has the correct source IP address.
Add a static route to the backup ISP, so that when the primary ISP is unavailable, the default route comes into effect and the traffic is directed through the backup ISP.

Configure the ingress and the egress interfaces on the firewall.

Egress interfaces can be in the same zone.

Select
Network
Interfaces
and select the interface you want to configure.
The interface configuration on the firewall used in this example is as follows:
Ethernet 1/19 connected to the primary ISP:
Zone: TwoISP
IP Address: 1.1.1.2/30
Virtual Router: Default
Ethernet 1/20 connected to the backup ISP:
Zone: TwoISP
IP Address: 2.2.2.2/30
Virtual Router: Default
Ethernet 1/2 is the ingress interface, used by the network clients to connect to the internet:
Zone: Corporate
IP Address: 192.168. 54.1/24
Virtual Router: Default
To save the interface configuration, click
OK
.

On the virtual router, add a static route to the backup ISP.

Select
Network
Virtual Router
and select the
default
link to open the Virtual Router dialog.
Select
Static Routes
and click
Add
. Enter a
Name
for the route and specify the
Destination
IP address for which you are defining the static route. In this example, we use 0.0.0.0/0 for all traffic.
Select the
IP Address
radio button and set the
Next Hop
IP address for your router that connects to the backup internet gateway (you cannot use a domain name for the next hop). In this example, 2.2.2.1.
Specify a cost metric for the route.

Click
OK
twice to save the virtual router configuration.

Create a PBF rule that directs traffic to the interface that is connected to the primary ISP.

Make sure to exclude traffic destined to internal servers/IP addresses from PBF. Define a negate rule so that traffic destined to internal IP addresses is not routed through the egress interface defined in the PBF rule.

Select

Policies

Policy Based Forwarding

and click

Add

.

Give the rule a descriptive

Name

in the

General

tab.

In the

Source

tab, set the

Source Zone

; in this example, the zone is Corporate.

In the

Destination/Application/Service

tab, set the following:

In the Destination Address section,

Add

the IP addresses or address range for servers on the internal network or create an address object for your internal servers. Select

Negate

to exclude the IP addresses or address object listed above from using this rule.

In the Service section,

Add

the

service-http

and

service-https

services to allow HTTP and HTTPS traffic to use the default ports. For all other traffic that is allowed by security policy, the default route will be used.

To forward all traffic using PBF, set the Service to

Any

.



Specify where to forward traffic.

In the
Forwarding
tab, specify the interface to which you want to forward traffic and enable path monitoring.
To forward traffic, set the
Action
to
Forward
, and select the
Egress Interface
and specify the
Next Hop
. In this example, the egress interface is ethernet1/19, and the next hop IP address is 1.1.1.1 (you cannot use a FQDN for the next hop).

Enable
Monitor
and attach the default monitoring profile to trigger a failover to the backup ISP. In this example, we do not specify a target IP address to monitor. The firewall will monitor the next hop IP address; if this IP address is unreachable, the firewall will direct traffic to the default route specified on the virtual router.
(
Required if you have asymmetric routes
) Select
Enforce Symmetric Return
to ensure that return traffic from the Corporate zone to the internet is forwarded out on the same interface through which traffic ingressed from the internet.
NAT ensures that the traffic from the internet is returned to the correct interface/IP address on the firewall.
Click
OK
to save the changes.



Create NAT rules based on the egress interface and ISP. These rules ensure that the correct source IP address is used for outbound connections.

Select

Policies

NAT

and click

Add

.

In this example, the NAT rule we create for each ISP is as follows:

NAT for Primary ISP

In the

Original Packet

tab,

Source Zone

: Corporate

Destination Zone

: TwoISP

In the

Translated Packet

tab, under Source Address Translation

Translation Type

: Dynamic IP and Port

Address Type

: Interface Address

Interface

: ethernet1/19

IP Address

: 1.1.1.2/30

NAT for Backup ISP

In the

Original Packet

tab,

Source Zone

: Corporate

Destination Zone

: TwoISP

In the

Translated Packet

tab, under Source Address Translation

Translation Type

: Dynamic IP and Port

Address Type

: Interface Address

Interface

: ethernet1/20

IP Address

: 2.2.2.2/30



Create security policy to allow outbound access to the internet.

To safely enable applications, create a simple rule that allows access to the internet and attach the security profiles available on the firewall.

Select

Policies

Security

and click

Add

.

Give the rule a descriptive

Name

in the

General

tab.

In the

Source

tab, set the

Source Zone

to Corporate.

In the

Destination

tab, Set the

Destination Zone

to TwoISP.

In the

Service/ URL Category

tab, leave the default

application-default

.

In the

Actions

tab, complete these tasks:

Set the
Action Setting
to
Allow
.
Attach the default profiles for Antivirus, Anti-Spyware, Vulnerability Protection and URL Filtering, under
Profile Setting.

Under

Options

, verify that logging is enabled at the end of a session. Only traffic that matches a security rule is logged.



Save the policies to the running configuration on the firewall.

Click

Commit

.

Verify that the PBF rule is active and that the primary ISP is used for internet access.

Launch a web browser and access a web server. On the firewall, check the traffic log for web-browsing activity.
From a client on the network, use the ping utility to verify connectivity to a web server on the internet, and check the traffic log on the firewall.
C:\Users\pm-user1>
ping 198.51.100.6 
Pinging 198.51.100.6 with 32 bytes of data: 
Reply from 198.51.100.6: bytes=32 time=34ms TTL=117 
Reply from 198.51.100.6: bytes=32 time=13ms TTL=117 
Reply from 198.51.100.6: bytes=32 time=25ms TTL=117 
Reply from 198.51.100.6: bytes=32 time=3ms TTL=117 
Ping statistics for 198.51.100.6: 
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), 
Approximate round trip times in milliseconds: 
    Minimum = 3ms, Maximum = 34ms, Average = 18ms 

To confirm that the PBF rule is active, use the following CLI command:

admin@PA-NGFW> 
show pbf rule all 
Rule       ID    Rule State Action   Egress IF/VSYS  NextHop 
========== === ========== ====== ==============  
Use ISP-Pr 1 Active     Forward ethernet1/1 1.1.1.1 

Verify that the failover to the backup ISP occurs and that the Source NAT is correctly applied.

Unplug the connection to the primary ISP.

Confirm that the PBF rule is inactive with the following CLI command:

admin@PA-NGFW> 
show pbf rule all 
Rule       ID    Rule State Action   Egress IF/VSYS  NextHop 
========== === ========== ====== ============== === 
Use ISP-Pr 1 Disabled Forward ethernet1/19     1.1.1.1 

Access a web server, and check the traffic log to verify that traffic is being forwarded through the backup ISP.



View the session details to confirm that the NAT rule is working properly.

admin@PA-NGFW> 
show session all 
--------------------------------------------------------- 
ID Application    State   Type Flag Src[Sport]/Zone/Proto (translated IP[Port]) Vsys Dst[Dport]/Zone (translated IP[Port]) 
--------------------------------------------------------- 
87212 ssl ACTIVE  FLOW  NS   192.168.54.56[53236]/Corporate/6  (2.2.2.2[12896]) vsys1 204.79.197.200[443]/TwoISP (204.79.197.200[443]) 

Obtain the session identification number from the output and view the session details.

The PBF rule is not used and hence is not listed in the output.

admin@PA-NGFW> 
show session id 87212 
Session           87212 
c2s flow: 
                source:      192.168.54.56 [Corporate] 
                dst:         204.79.197.200 
                proto:       6 
                sport:       53236           dport:      443 
                state:       ACTIVE          type:       FLOW 
                src user:    unknown 
                dst user:    unknown 
s2c flow: 
                source:      204.79.197.200 [TwoISP] 
                dst:         2.2.2.2 
                proto:       6 
                sport:       443             dport:      12896 
                state:       ACTIVE          type:       FLOW 
                src user:    unknown 
                dst user:    unknown 
start time                    : Wed Nov5 11:16:10 2014 
        timeout                       : 1800 sec 
        time to live                  : 1757 sec 
        total byte count(c2s)         : 1918 
        total byte count(s2c)         : 4333 
        layer7 packet count(c2s)      : 10 
        layer7 packet count(s2c)      : 7 
        vsys                          : vsys1 
        application                   : ssl 
        rule                          : Corp2ISP 
        session to be logged at end   : True 
        session in session ager       : True 
        session synced from HA peer   : False 
        address/port translation      : source 
       
 nat-rule                      : NAT-Backup ISP(vsys1) 
        layer7 processing             : enabled 
        URL filtering enabled         : True 
        URL category                  : search-engines 
        session via syn-cookies       : False 
        session terminated on host    : False 
        session traverses tunnel      : False 
        authentication portal session        : False 
        
ingress interface             : ethernet1/2 
        egress interface              : ethernet1/20 
        session QoS rule              : N/A (class 4)