How to Supress Hello packets on an interface enabled for OSPF

Discussion in 'Cisco' started by jimbo, Jul 10, 2005.

  1. jimbo

    jimbo Guest

    As I understand it, enabling an interface to join an area with the
    NETWORK command, also causes Hello packets to be sent out the
    interface. But if its a stub network, and you want it advertised, but
    there is no need for Hello packets to be sent out the interface, how do
    you suppress them?

    The passive-interface command seems to be discouraged in OSPF, since
    there is far more granular control over which interfaces are affected
    by the network command.

    The "redistribute connected subnets" could be used after entering the
    network command with a very restrictive mask that advertises only
    non-stub network interface(s). But that seems to open a whole new can
    of redristribute issues.

    This is simple to do, right?

    jimbo, Jul 10, 2005
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  2. jimbo

    Guest Guest

    although i would use the passive interface command, you can create an ACL
    for and and block the hello packets too.

    2nd Law of Thermodynamics: Chaos will Reign.

    Guest, Jul 10, 2005
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  3. Use " ip ospf demand-circuit" on one side of the link .But remember it
    will only work for p-t-p or p-t-mp ospf networks

    Example :

    RouterA# show run interface Serial0
    interface Serial 0
    encapsulation frame-relay
    ip address
    ip ospf network-type point-to-mutipoint
    ip ospf demand-circuit

    sarabjit.herr, Jul 11, 2005
  4. jimbo

    jimbo Guest

    Right. Thank you. I was aware of that command, but I just want to
    supress hellos on the stub networks in the system. Seems no need to
    waste the bandwidth sending Hellos out a link that will never be
    responded to.

    jimbo, Jul 12, 2005
  5. Yes ..Ip ospf demand-circuit will suppress sending hello packets .
    sarabjit.herr, Jul 17, 2005
  6. jimbo

    dbn58 Guest

    Hello Jimbo,

    (1) use the network command with teh appropriate network address and
    wildcard mask to include the required interface(s) into the scope of your
    OSPF process. Do this even for the stub networks.
    (2) use the 'passive' command to prevent interfaces to stub networks from
    sending hello packets.
    Result: OSPF will know the connected networks, but will not bother stub
    networks with hello packets. All networks are known as OSPF networks. All
    configuration can be done inside the 'router ospf' block

    (1) use the network command for all interfaces to all non-stub networks,
    where OSPF routers reside you want to establish neigborships with
    (2) use 'redistribut connected subnets' to make all other interfaces known
    to ospf
    Result: OSPF will know non-stub networks as OSPF networks, and other
    connected networks as external rotes. This router will become an ASBR. Can
    induce design constraints as your network grows

    Another approach:
    (1) treat non-stub networks and stub networks the same by using appropriate
    network commands etc
    (2) use ACLs to block OSPF multicasts on the interfaces you do not want to
    build OSPF neighborships
    Result: almost the same as for the solution I consider 'best'. But the
    configuration is less local and is spread over several parts of the conf
    script: the 'router ospf' block, the regieon where the ACLs reside, and all
    interfaces to stub networks

    dbn58, Jul 17, 2005
  7. jimbo

    jimbo Guest

    Good stuff. That is pretty much where I had arrived at. I saw a text
    somewhere that indicated the 'passive' command was unecessary in OSPF -
    but that is simply not so.

    jimbo, Jul 17, 2005
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