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18318 Views 10 Replies Latest reply: Sep 25, 2010 8:23 AM by Scott Morris - CCDE/4xCCIE/2xJNCIE RSS

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OSPF hello and dead timers

Sep 9, 2009 6:06 PM

Jimmy P 169 posts since
Jun 14, 2009

What is the best practice, when it comes to solving OSPF  hello and dead timers mismatch errors.

  • John 2,289 posts since
    Jan 17, 2009
    Currently Being Moderated
    1. Sep 9, 2009 6:22 PM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Hi

     

    Not exactly sure what you mean, can you expand on that.

     

    The Hello and the Dead Times must match and if they don't they have to be changed to match but that is probably not what you mean.

     

     

     

    Regards

     

    John

  • Currently Being Moderated
    3. Sep 9, 2009 6:53 PM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Hi!

     

    If router 1 is directly connected to router 2, you can change the ospf network type to point to point or broadcast on router one and that should solve that issue. (ip ospf network point-to-point.  Manually changing the hello and dead interval timers would cause your neighbor relationship to form, but your routers will not be "truly" adjacent and you may in fact find inconsistantcies in your opsf database.

     

    Erick

  • John 2,289 posts since
    Jan 17, 2009
    Currently Being Moderated
    4. Sep 9, 2009 6:53 PM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Hi

     

    I am no expert and i am still learning myself but from everything i have read; those timers have to match so all 3 would have to be changed.

     

    Perhaps someone with more experience can confirm this is correct.

     

     

    Regards

     

    John

  • TX858 183 posts since
    Sep 29, 2008
    Currently Being Moderated
    5. Sep 9, 2009 7:02 PM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Do show ip ospf neighbors to see if neighbor is in the list. If not, see if you can ping ping the router that's supposed to be the neighbor. If you cannot ping it and you're sure that the near interface is up, check neighbor interface for shut. If you can ping the neighbor router but it's not listed in output of show ip ospf neighbors command, check the timers on both the near and far routers to be sure they match. You can view the timers using show ip ospf interface.

     

    Below is output from this scenario. Neighbor is there and listed in show ip ospf neighbors output. I then changed the hello interval on the PHX router and run show ip ospf neighbors again - neighbor is not gone from the output. I then ping the neighbor and it replies. I then look at the timers using show ip ospf interface command. You can see that PHX is set to Hello 20, Dead 80 on PHX and Hello 10, Dead 40 on KFX. Mismatch. Fix the mismatch and the neighbor shows up again.

     

    I may not have used the above order but you should get the idea from the output below.

     

    Note: I wouldn't rely on IOS to automatically change the dead-interval when you change the hello. I change both.

     

    See Attached PDF

     

    =============

     


    PHX#show ip ospf int
    Serial0/0 is up, line protocol is up
      Internet Address 10.2.1.2/30, Area 1
      Process ID 25, Router ID 10.5.1.1, Network Type POINT_TO_POINT, Cost: 64
      Transmit Delay is 1 sec, State POINT_TO_POINT,
      Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
        oob-resync timeout 40
        Hello due in 00:00:09
      Index 2/2, flood queue length 0
      Next 0x0(0)/0x0(0)
      Last flood scan length is 1, maximum is 1
      Last flood scan time is 0 msec, maximum is 0 msec
      Neighbor Count is 1, Adjacent neighbor count is 1
        Adjacent with neighbor 222.222.222.222
      Suppress hello for 0 neighbor(s)
    FastEthernet0/0 is up, line protocol is up
      Internet Address 10.5.1.1/28, Area 1
      Process ID 25, Router ID 10.5.1.1, Network Type BROADCAST, Cost: 1
      Transmit Delay is 1 sec, State WAITING, Priority 1
      No designated router on this network
      No backup designated router on this network
      Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
        oob-resync timeout 40
        Hello due in 00:00:09
        Wait time before Designated router selection 00:00:09
      Index 1/1, flood queue length 0
      Next 0x0(0)/0x0(0)
      Last flood scan length is 0, maximum is 0
      Last flood scan time is 0 msec, maximum is 0 msec
      Neighbor Count is 0, Adjacent neighbor count is 0
      Suppress hello for 0 neighbor(s)

     

    PHX#show ip ospf nei

     

    Neighbor ID     Pri   State           Dead Time   Address         Interface
    222.222.222.222   0   FULL/  -        00:00:37    10.2.1.1        Serial0/0

     


    PHX#config t
    Enter configuration commands, one per line.  End with CNTL/Z.
    PHX(config)#int s0/0
    PHX(config-if)#ip ospf ****
    PHX(config-if)#ip ospf hello-interval 20
    PHX(config-if)#ip ospf dead-interval 80
    PHX(config-if)#end

     

    PHX#show ip ospf neighbor
    [ Note that neighbor is now gone ]
    PHX#

     

    PHX#show ip ospf int
    PHX#show ip ospf interface s0/0
    Serial0/0 is up, line protocol is up
      Internet Address 10.2.1.2/30, Area 1
      Process ID 25, Router ID 10.5.1.1, Network Type POINT_TO_POINT, Cost: 64
      Transmit Delay is 1 sec, State POINT_TO_POINT,
      Timer intervals configured, Hello 20, Dead 80, Wait 80, Retransmit 5
        oob-resync timeout 80
        Hello due in 00:00:03
      Index 2/2, flood queue length 0
      Next 0x0(0)/0x0(0)
      Last flood scan length is 0, maximum is 1
      Last flood scan time is 0 msec, maximum is 0 msec
      Neighbor Count is 0, Adjacent neighbor count is 0
      Suppress hello for 0 neighbor(s)
    PHX#

     

    PHX#ping 10.2.1.1

     

    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 10.2.1.1, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
    PHX#

     

    PHX#config t
    Enter configuration commands, one per line.  End with CNTL/Z.
    PHX(config)#int s0/0
    PHX(config-if)#no ip ospf hello
    PHX(config-if)#no ip ospf hello-interval
    PHX(config-if)#no ip ospf dead
    PHX(config-if)#end
    PHX#
    PHX#show ip ospf neighbor

     

    Neighbor ID     Pri   State           Dead Time   Address         Interface
    222.222.222.222   0   FULL/  -        00:00:38    10.2.1.1        Serial0/0
    PHX#

     

    HTH,

    TX

     

    Message was edited by: TX858 Added attachment for easier reading.

    Attachments:
  • Brian McGahan - 4 x CCIE, CCDE 642 posts since
    May 29, 2008
    Currently Being Moderated
    6. Sep 9, 2009 7:26 PM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Hi Netmax,

     

    Per RFC 2328, OSPF Version 2, the hello interval and the dead interval must match in order for neighbors on a link to become adjacent.

     

    9.5.  Sending Hello packets
    
            Hello packets are sent out each functioning router interface.
            They are used to discover and maintain neighbor
            relationships.[6] On broadcast and NBMA networks, Hello Packets
            are also used to elect the Designated Router and Backup
            Designated Router.
    
            The format of an Hello packet is detailed in Section A.3.2.  The
            Hello Packet contains the router's Router Priority (used in
            choosing the Designated Router), and the interval between Hello
            Packets sent out the interface (HelloInterval).  The Hello
            Packet also indicates how often a neighbor must be heard from to
            remain active (RouterDeadInterval).  Both HelloInterval and
            RouterDeadInterval must be the same for all routers attached to
            a common network...
    

     

    This means that all routers on a segment, whether it be a point-to-point link such as PPP, or a multipoint link such as Ethernet, must have both the same hello and dead intervals.  Normally this is controlled in Cisco IOS per the OSPF network type, where if the network type matches the hello and dead intervals will automatically match.  You can also manually change the hello and dead intervals with the interface level commands "ip ospf hello-interval" and "ip ospf dead-interval".  Usually this is done in order to provide for faster convergence, through features such as sub-second hellos in OSPF.

     

    HTH,

     

    Brian McGahan, CCIE #8593 (R&S/SP/Security)
    bmcgahan@INE.com

  • John 2,289 posts since
    Jan 17, 2009
    Currently Being Moderated
    7. Sep 10, 2009 4:13 AM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    Hi

     

    With regards to real life and those 3 routers you mentioned, i suppose you would not get 3 live routers not matching in real life unless 2 of them were new and just installed. As you install one you make it work then move onto the other one.

     

     

     

    Regards

     

    John

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,396 posts since
    Oct 7, 2008
    Currently Being Moderated
    8. Sep 10, 2009 5:09 AM (in response to John)
    Re: OSPF hello and dead timers

    Or plan ahead and just have them all work.  

  • Ganesh 68 posts since
    Oct 4, 2009
    Currently Being Moderated
    9. Sep 25, 2010 5:35 AM (in response to Jimmy P)
    Re: OSPF hello and dead timers

    once adjacnecy is formed after if i change the  hello and dead timer then the neighbourship will break ?

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,396 posts since
    Oct 7, 2008
    Currently Being Moderated
    10. Sep 25, 2010 8:23 AM (in response to Ganesh)
    Re: OSPF hello and dead timers

    Yes, because there will then be a mismatch in the hello's.

     

    "debug ip ospf adjacency" is the best way to see all that.  You'll get output with "C" for Configured values and "R" for Received ones.

     

    Scott

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