Configure ECMP on a Virtual Router

Use the following procedure to enable ECMP on a virtual router. The prerequisites are to:
  • Specify the interfaces that belong to a virtual router (
    Network
    Virtual Routers
    Router Settings
    General
    ).
  • Specify the IP routing protocol.
Enabling, disabling, or changing ECMP for an existing virtual router causes the system to restart the virtual router, which might cause sessions to be terminated.
  1. Enable ECMP for a virtual router.
    1. Select
      Network
      Virtual Routers
      and select the virtual router on which to enable ECMP.
    2. Select
      Router Settings
      ECMP
      and select
      Enable
      .
  2. (
    Optional
    ) Enable symmetric return of packets from server to client.
    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. The
    Symmetric Return
    setting overrides load balancing. This behavior occurs only for traffic flows from the server to the client.
  3. Specify the maximum number of equal-cost paths (to a destination network) that can be copied from the Routing Information Base (RIB) to the Forwarding Information Base (FIB).
    For
    Max Path
    allowed, enter
    2
    ,
    3
    , or
    4
    . Default: 2.
  4. Select the load-balancing algorithm for the virtual router. For more information on load-balancing methods and how they differ, see ECMP Load-Balancing Algorithms.
    For
    Load Balance
    , select one of the following options from the
    Method
    list:
    • IP Modulo
      (default)—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 (select hash options in Step 5):
      • Use a hash of the source address (available in PAN-OS 8.0.3 and later releases).
      • Use a hash of the source and destination IP addresses (the default IP hash method).
    • Balanced Round Robin
      —Uses round robin among the ECMP paths and re-balances paths when the number of paths changes.
    • Weighted Round Robin
      —Uses round robin and a relative weight to select from among ECMP paths. Specify the weights in Step 6 below.
  5. (
    IP Hash only
    ) Configure IP Hash options.
    If you selected
    IP Hash
    as the
    Method
    :
    1. Select
      Use Source Address Only
      (available in PAN-OS 8.0.3 and later releases) if you want to ensure all sessions belonging to the same source IP address always take the same path from available multiple paths. This IP hash option provides path stickiness and eases troubleshooting. If you don’t select this option or you’re using a release prior to PAN-OS 8.0.3, the IP hash is based on the source and destination IP addresses (the default IP hash method).
      If you select
      Use Source Address Only
      , you shouldn’t push the configuration from Panorama to firewalls running PAN-OS 8.0.2, 8.0.1, or 8.0.0.
    2. Select
      Use Source/Destination Ports
      if you want to use source or destination port numbers in the
      IP Hash
      calculation.
      Enabling this option along with
      Use Source Address Only
      will randomize path selection even for sessions belonging to the same source IP address.
    3. Enter a
      Hash Seed
      value (an integer with a maximum of nine digits). Specify a
      Hash Seed
      value to further randomize load balancing. Specifying a hash seed value is useful if you have a large number of sessions with the same tuple information.
  6. (
    Weighted Round Robin only
    ) Define a weight for each interface in the ECMP group.
    If you selected
    Weighted Round Robin
    as the
    Method
    , define a weight for each of the interfaces that are the egress points for traffic to be routed to the same destinations (that is, interfaces that are part of an ECMP group, such as the interfaces that provide redundant links to your ISP or interfaces to the core business applications on your corporate network).
    The higher the weight, the more often that equal-cost path will be selected for a new session.
    Give higher speed links a higher weight than a slower links so that more of the ECMP traffic goes over the faster link.
    1. Create an ECMP group by clicking
      Add
      and selecting an
      Interface
      .
    2. Add
      the other interfaces in the ECMP group.
    3. Click on
      Weight
      and specify the relative weight for each interface (range is 1-255; default is 100).
  7. Save the configuration.
    1. Click
      OK
      .
    2. At the ECMP Configuration Change prompt, click
      Yes
      to restart the virtual router. Restarting the virtual router might cause existing sessions to be terminated.
      This message displays only if you are modifying an existing virtual router with ECMP.
  8. Commit your changes.
    Commit
    the configuration.

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