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General Settings of a Logical Router

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General Settings of a Logical Router

Name a logical router, specify its interfaces, and optionally configure ECMP.

Network > Routing > Logical Routers > General

When you enable Advanced Routing (DeviceSetupManagement), the firewall uses a logical router for static and dynamic routing. A logical router requires that you assign a name and Layer 3 interfaces as described in the following table. The Advanced Routing route engine on the firewall supports only one logical router.

You can optionally configure Equal Cost Multiple Path (ECMP) for the logical router. ECMP processing is a networking feature that enables the firewall to use up to four equal-cost routes to the same destination. Without this feature, if there are multiple equal-cost routes to the same destination, the virtual router chooses one of those routes from the routing table and adds it to its forwarding table; it will not use any of the other routes unless there is an outage in the chosen route. Enabling ECMP functionality on a virtual router allows the firewall have up to four equal-cost paths to a destination in its forwarding table, allowing the firewall to:

Load balance flows (sessions) to the same destination over multiple equal-cost links.
Make use of the available bandwidth on all links to the same destination rather than leave some links unused.
Dynamically shift traffic to another ECMP member to the same destination if a link fails, rather than waiting for the routing protocol or RIB table to elect an alternative path, which can help reduce down time when links fail.

ECMP load balancing is done at the session level, not at the packet level. This means the firewall chooses an equal-cost path at the start of a new session, not each time the firewall receives a packet.

Logical Router General Settings	Description
Name	Specify a name to describe the logical router (up to 31 characters). The name is case-sensitive and must be unique. Use only letters, numbers, spaces, hyphens, and underscores.
Interface	Add the Layer 3 interfaces that you want to include in the logical router. These interfaces can be used as outgoing interfaces in the logical router’s routing table. To specify the interface type, refer to Network > Interfaces. When you add an interface, its connected routes are added automatically.
ECMP
Enable	Enables Equal-Cost Multiple Path (ECMP) for the logical router.
Symmetric Return	(`Optional`) Select Symmetric Return to cause return packets to egress out the same interface on which the associated ingress packets arrived. That is, the firewall will use the ingress interface on which to send return packets, rather than use the ECMP interface, so the Symmetric Return setting overrides load balancing. This behavior occurs only for traffic flows from the server to the client.
Strict Source Path	By default, IKE and IPSec traffic originating at the firewall egresses an interface that the ECMP load-balancing method determines. Select Strict Source Path to ensure that IKE and IPSec traffic originating at the firewall always egresses the physical interface to which the source IP address of the IPSec tunnel belongs. You would enable Strict Source Path when the firewall has more than one ISP providing equal-cost paths to the same destination. The ISPs typically perform a Reverse Path Forwarding (RPF) check (or a different check to prevent IP address spoofing) to confirm that the traffic is egressing the same interface on which it arrived. Because ECMP by default would choose an egress interface based on the configured ECMP method (instead of choosing the source interface as the egress interface), that would not be what the ISP expects and the ISP could block legitimate return traffic. In this use case, enable Strict Source Path so that the firewall uses the egress interface that is the interface to which the source IP address of the IPSec tunnel belongs.
Max Path	Select the maximum number of equal-cost paths: (2, 3, or 4) to a destination network that can be copied from the RIB to the FIB. Default is 2.
Load-Balancing Method	Choose one of the following ECMP load-balancing algorithms to use on the virtual router. ECMP load balancing is done at the session level, not at the packet level. This means that the firewall (ECMP) chooses an equal-cost path at the start of a new session, not each time a packet is received. IP Modulo—By default, the virtual router load balances sessions using this option, which uses a hash of the source and destination IP addresses in the packet header to determine which ECMP route to use. IP Hash—There are two IP hash methods that determine which ECMP route to use: If you select IP Hash, by default the firewall uses a hash of the source and destination IP addresses. Alternatively, you can select Use Source Address Only (available in PAN-OS 8.0.3 and later releases). This IP hash method ensures that all sessions belonging to the same source IP address always take the same path. Optionally select Use Source/Destination Ports to include the ports in either hash calculation. You can also enter a Hash Seed value (an integer) to further randomize load balancing. Weighted Round Robin—This algorithm can be used to take into consideration different link capacities and speeds. Upon choosing this algorithm, the Interface window opens. Click Add and select an Interface to be included in the weighted round robin group. For each interface, enter the Weight to be used for that interface. Weight defaults to 100; range is 1-255. The higher the weight for a specific equal-cost path, the more often that equal-cost path will be selected for a new session. A higher speed link should be given a higher weight than a slower link, so that more of the ECMP traffic goes over the faster link. Click Add again to add another interface and weight. Balanced Round Robin—Distributes incoming ECMP sessions equally across links.

Network > Routing > Logical Routers

Static Routes for a Logical Router