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 (
Device
Setup
Management
), 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.

Recommended For You