Title: UTM: Interoperability issue for OSPF with tunnel-interfaces between 5.9.x.x, 5.8.x.x and 6.x.x.x. (SW10735)
  • Title

    UTM: Interoperability issue for OSPF with tunnel-interfaces between 5.9.x.x, 5.8.x.x and 6.x.x.x.
  • Resolution

    Article Applies To:

    Gen6 SM E10000 series: NSA E10800, NSA E10400, NSA E10200, NSA E10100
    Gen6 SM 9000 series: NSA 9600, NSA 9400, NSA 9200
    Gen6 NSA series: NSA 6600, NSA 5600, NSA 4600, NSA 3600

    Gen5 NSA E-Class series: NSA E8510, E8500, NSA E7500, NSA E6500, NSA E5500
    Gen5 NSA series: NSA 5000, NSA 4500, NSA 3500, NSA 2400, NSA 2400 MX, NSA 240, NSA 220, NSA 220 /W. NSA 250M, NSA 250M /W.
    Gen5 TZ Series: TZ 215, TZ 215 W, TZ 210, TZ 210 W

    Firmware/Software Version: SonicOS 5.8.x, 5.9.x, 6.x

    Services: Routing

    Problem Definition:

    There exists an interoperability issue for OSPF over tunnel-interfaces with 5.9.x.x vs. 5.8.x.x or 6.x.x.x.   By default, both sides of an OSPF adjacency tell the other side what they believe the MTU is on the interface over which they are sending packets. If one side gets a different (actually smaller) MTU than what it believes is the MTU, the adjacency is not formed. Previous to, we always used an MTU of 1500 on tunnel-interfaces. In SonicOS 5.9, a more realistic MTU (1446) was assigned to tunnel-interfaces populated in ZebOS. 

    Unfortunately, this breaks compatibility with the unnumbered tunnel-interface implementation on 5.8.x and 6.x.x.

    Resolution or Workaround:

    The following workaround has to be configured from the CLI. 

    The OSPF CLI provides a command that will force OSPF to ignore MTU differences on a particular interface. In this case, it's the 5.9.x.x OSPF code that complains about the MTU since the value sent from 5.8.x and 6.x.x is 1500 - larger than the 1446 MTU for the tunnel-interface in 5.9.x.x.

    On the SonicOS 5.9.x.x appliance do the following:

    1. Enter Configuration mode on the SonicOS CLI.
    2. Navigate to Routing, then OSPF in the CLI.
    3. Show the OSPF interfaces with the "show ip ospf interface" command. You should see the tunnel-interface you want to configure in the list.
    4. Enter configuration mode in the OSPF CLI with the "configure terminal" command.
    5. Configure the tunnel interface with the "interface " command.
    6. Disable the MTU comparison with the "ip ospf mtu-ignore" command.
    7. Exit back to the non-config OSPF prompt.
    8. Save the change with the "write file" command.
    9. Exit out of the CLI config.

    Here is an example:

    admin@> conf
    config# routing
    (config-routing)# ospf

    ZebOS version 7.7.0 IPIRouter 7/2009
    ARS OSPF>show ip ospf interface
    TI2 is up, line protocol is up
      Internet Address, Area, MTU 1446
      Process ID 0, Router ID, Network Type POINTOPOINT, Cost: 1
      Transmit Delay is 1 sec, State Point-To-Point
      Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
        Hello due in 00:00:04
      Neighbor Count is 1, Adjacent neighbor count is 1
      Crypt Sequence Number is 1385167419
      Hello received 178 sent 178, DD received 3 sent 4
      LS-Req received 1 sent 1, LS-Upd received 3 sent 3
      LS-Ack received 2 sent 3, Discarded 0
    ARS OSPF>configure terminal
    ARS OSPF(config)>interface TI2
    ARS OSPF(config-if)>ip ospf mtu-ignore
    ARS OSPF(config-if)>exit
    ARS OSPF(config)>exit
    ARS OSPF>write file
    Configuration saved to OSPF
    ARS OSPF>exit
    (config-routing)# end
    config # end

Authored by: Guru Corner on Sun, Jul 19th, 2015 at 6:00 PM
This question has been viewed 3460 times so far.
Online URL: http://kb.guru-corner.com/question.php?ID=324

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