GRE Tunnel Overview
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Next-Generation Firewall Docs
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PAN-OS 9.1 (EoL)
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- Cloud Management of NGFWs
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- Management Interfaces
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- Launch the Web Interface
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- Define Access to the Web Interface Tabs
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- Reset the Firewall to Factory Default Settings
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- Plan Your Authentication Deployment
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- HA Overview
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- Prerequisites for Active/Active HA
- Configure Active/Active HA
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- Use Case: Configure Active/Active HA with Route-Based Redundancy
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- Use Case: Configure Active/Active HA with Floating IP Address Bound to Active-Primary Firewall
- Use Case: Configure Active/Active HA with Source DIPP NAT Using Floating IP Addresses
- Use Case: Configure Separate Source NAT IP Address Pools for Active/Active HA Firewalls
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- Reference: HA Synchronization
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- User-ID Overview
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- App-ID Overview
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- Apply Tags to an Application Filter
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- Best Practices for Securing Your Network from Layer 4 and Layer 7 Evasions
- Set Up Antivirus, Anti-Spyware, and Vulnerability Protection
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- Decryption Overview
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- Keys and Certificates for Decryption Policies
- SSL Forward Proxy
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- Perfect Forward Secrecy (PFS) Support for SSL Decryption
- SSL Decryption and Subject Alternative Names (SANs)
- High Availability Support for Decrypted Sessions
- Decryption Mirroring
- Configure SSL Forward Proxy
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- Verify Decryption
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- How Decryption Broker Works
- Layer 3 Security Chain Guidelines
- Configure Decryption Broker with One or More Layer 3 Security Chain
- Transparent Bridge Security Chain Guidelines
- Configure Decryption Broker with a Single Transparent Bridge Security Chain
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- Activate Free Licenses for Decryption Features
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- About Palo Alto Networks URL Filtering Solution
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- Plan Your URL Filtering Deployment
- URL Filtering Best Practices
- Activate The Advanced URL Filtering Subscription
- Configure URL Filtering
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- Tap Interfaces
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- Layer 2 and Layer 3 Packets over a Virtual Wire
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- DNS Overview
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- Configure a DNS Proxy Object
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- DNS Proxy Rule and FQDN Matching
- Dynamic DNS Overview
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- NAT Rule Capacities
- Dynamic IP and Port NAT Oversubscription
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- Translate Internal Client IP Addresses to Your Public IP Address (Source DIPP NAT)
- Enable Clients on the Internal Network to Access your Public Servers (Destination U-Turn NAT)
- Enable Bi-Directional Address Translation for Your Public-Facing Servers (Static Source NAT)
- Configure Destination NAT with DNS Rewrite
- Configure Destination NAT Using Dynamic IP Addresses
- Modify the Oversubscription Rate for DIPP NAT
- Reserve Dynamic IP NAT Addresses
- Disable NAT for a Specific Host or Interface
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- Policy Types
- Policy Objects
- Track Rules Within a Rulebase
- Enforce Policy Rule Description, Tag, and Audit Comment
- Move or Clone a Policy Rule or Object to a Different Virtual System
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- External Dynamic List
- Built-in External Dynamic Lists
- Configure the Firewall to Access an External Dynamic List
- Retrieve an External Dynamic List from the Web Server
- View External Dynamic List Entries
- Exclude Entries from an External Dynamic List
- Enforce Policy on an External Dynamic List
- Find External Dynamic Lists That Failed Authentication
- Disable Authentication for an External Dynamic List
- Register IP Addresses and Tags Dynamically
- Use Dynamic User Groups in Policy
- Use Auto-Tagging to Automate Security Actions
- CLI Commands for Dynamic IP Addresses and Tags
- Application Override Policy
- Test Policy Rules
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PAN-OS 11.1 & Later
- PAN-OS 11.1 & Later
- PAN-OS 11.0 (EoL)
- PAN-OS 10.2
- PAN-OS 10.1
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- Tap Interfaces
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- Layer 2 and Layer 3 Packets over a Virtual Wire
- Port Speeds of Virtual Wire Interfaces
- LLDP over a Virtual Wire
- Aggregated Interfaces for a Virtual Wire
- Virtual Wire Support of High Availability
- Zone Protection for a Virtual Wire Interface
- VLAN-Tagged Traffic
- Virtual Wire Subinterfaces
- Configure Virtual Wires
- Configure a PPPoE Client on a Subinterface
- Configure an IPv6 PPPoE Client
- Configure an Aggregate Interface Group
- Configure Bonjour Reflector for Network Segmentation
- Use Interface Management Profiles to Restrict Access
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- DHCP Overview
- Firewall as a DHCP Server and Client
- Firewall as a DHCPv6 Client
- DHCP Messages
- Dynamic IPv6 Addressing on the Management Interface
- Configure an Interface as a DHCP Server
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- Configure the Management Interface as a DHCP Client
- Configure the Management Interface for Dynamic IPv6 Address Assignment
- Configure an Interface as a DHCP Relay Agent
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- DNS Overview
- DNS Proxy Object
- DNS Server Profile
- Multi-Tenant DNS Deployments
- Configure a DNS Proxy Object
- Configure a DNS Server Profile
- Use Case 1: Firewall Requires DNS Resolution
- Use Case 2: ISP Tenant Uses DNS Proxy to Handle DNS Resolution for Security Policies, Reporting, and Services within its Virtual System
- Use Case 3: Firewall Acts as DNS Proxy Between Client and Server
- DNS Proxy Rule and FQDN Matching
-
- NAT Rule Capacities
- Dynamic IP and Port NAT Oversubscription
- Dataplane NAT Memory Statistics
-
- Translate Internal Client IP Addresses to Your Public IP Address (Source DIPP NAT)
- Create a Source NAT Rule with Persistent DIPP
- PAN-OS
- Strata Cloud Manager
- Enable Clients on the Internal Network to Access your Public Servers (Destination U-Turn NAT)
- Enable Bi-Directional Address Translation for Your Public-Facing Servers (Static Source NAT)
- Configure Destination NAT with DNS Rewrite
- Configure Destination NAT Using Dynamic IP Addresses
- Modify the Oversubscription Rate for DIPP NAT
- Reserve Dynamic IP NAT Addresses
- Disable NAT for a Specific Host or Interface
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- Network Packet Broker Overview
- How Network Packet Broker Works
- Prepare to Deploy Network Packet Broker
- Configure Transparent Bridge Security Chains
- Configure Routed Layer 3 Security Chains
- Network Packet Broker HA Support
- User Interface Changes for Network Packet Broker
- Limitations of Network Packet Broker
- Troubleshoot Network Packet Broker
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- Enable Advanced Routing
- Logical Router Overview
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- Create a Static Route
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- Configure IPv4 Multicast
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- Create an IPv4 MRoute
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PAN-OS 11.2
- PAN-OS 11.2
- PAN-OS 11.1
- PAN-OS 11.0 (EoL)
- PAN-OS 10.2
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- PAN-OS 10.0 (EoL)
- PAN-OS 9.1 (EoL)
- PAN-OS 9.0 (EoL)
- PAN-OS 8.1 (EoL)
- Cloud Management and AIOps for NGFW
End-of-Life (EoL)
GRE Tunnel Overview
A Generic Routing Encapsulation (GRE) tunnel connects
two endpoints in a point-to-point, logical link.
A Generic Routing Encapsulation (GRE) tunnel
connects two endpoints (a firewall and another appliance) in a point-to-point,
logical link. The firewall can terminate GRE tunnels; you can route
or forward packets to a GRE tunnel. GRE tunnels are simple to use
and often the tunneling protocol of choice for point-to-point connectivity, especially
to services in the cloud or to partner networks.
Create a GRE tunnel when
you want to direct packets that are destined for an IP address to
take a certain point-to-point path, for example to a cloud-based
proxy or to a partner network. The packets travel through the GRE
tunnel (over a transit network such as the internet) to the cloud
service while on their way to the destination address. This enables
the cloud service to enforce its services or policies on the packets.
The following figure is an example of a GRE tunnel connecting
the firewall across the internet to a cloud service.
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For better performance and to avoid single points of failure,
split multiple connections to the firewall among multiple GRE tunnels
rather than use a single tunnel. Each GRE tunnel needs a tunnel
interface.
When the firewall allows a packet to pass (based on a policy
match) and the packet egresses to a GRE tunnel interface, the firewall
adds GRE encapsulation; it doesn’t generate a session. The firewall
does not perform a Security policy rule lookup for the GRE-encapsulated
traffic, so you don’t need a Security policy rule for the GRE traffic that the firewall
encapsulates. However, when the firewall receives GRE traffic, it
generates a session and applies all policies to the GRE IP header
in addition to the encapsulated traffic. The firewall treats the
received GRE packet like any other packet. Therefore:
- If the firewall receives the GRE packet on an interface that has the same zone as the tunnel interface associated with the GRE tunnel (for example, tunnel.1), the source zone is the same as the destination zone. By default, traffic is allowed within a zone (intrazone traffic), so the ingress GRE traffic is allowed by default.
- However, if you configured your own intrazone Security policy rule to deny such traffic, you must explicitly allow GRE traffic.
- Likewise, if the zone of the tunnel interface associated with the GRE tunnel (for example, tunnel.1) is a different zone from that of the ingress interface, you must configure a Security policy rule to allow the GRE traffic.
Because the firewall encapsulates the tunneled packet in a GRE
packet, the additional 24 bytes of GRE header automatically result
in a smaller Maximum Segment Size (MSS) in the
maximum transmission unit (MTU). If you don’t change the IPv4 MSS
Adjustment Size for the interface, the firewall reduces the MTU
by 64 bytes by default (40 bytes of IP header + 24 bytes of GRE
header). This means if the default MTU is 1,500 bytes, the MSS will
be 1,436 bytes (1,500 - 40 - 24 = 1,436). If you configure an MSS
Adjustment Size of 300 bytes, for example, the MSS will be only 1,176
bytes (1,500 - 300 - 24 = 1,176).
The firewall does not support routing a GRE or IPSec tunnel to
a GRE tunnel, but you can route a GRE tunnel to an IPSec tunnel.
Additionally:
- A GRE tunnel does not support QoS.
- The firewall does not support a single interface acting as both a GRE tunnel endpoint and a decryption broker.
- GRE tunneling does not support NAT between GRE tunnel endpoints.
If you need to connect to another vendor’s network, we
recommend you Set Up an IPSec Tunnel, not a GRE
tunnel; you should use a GRE tunnel only if that is the only point-to-point
tunnel mechanism that the vendor supports. You can also enable GRE
over IPSec if the remote endpoint requires that (Add GRE
Encapsulation). Add GRE encapsulation in cases where
the remote endpoint requires traffic to be encapsulated within a
GRE tunnel before IPSec encrypts the traffic. For example, some
implementations require multicast traffic to be encapsulated before
IPSec encrypts it. If this is a requirement for your environment
and the GRE tunnel and IPSec tunnel share the same IP address, Add
GRE Encapsulation when you set up the IPSec tunnel.
If you aren’t planning to terminate a GRE
tunnel on the firewall, but you want the ability to inspect and
control traffic passing through the firewall inside a GRE tunnel,
don’t create a GRE tunnel. Instead, perform Tunnel Content Inspection of GRE
traffic. With tunnel content inspection, you are inspecting and enforcing
policy on GRE traffic passing through the firewall, not creating
a point-to-point, logical link for the purpose of directing traffic.