Ip Route to NULL0?

Discussion in 'Cisco' started by Scott Townsend, Apr 24, 2006.

  1. We received a Router from an ISP and they have the Following Line in it.

    ip route A.B.C.0 255.255.255.0 Null0 254 permanent

    Where the local Ethernet Interface is: A.B.C.1 255.255.255.0

    What is the Purpose of this? If the Ethernet interface is Down, route all
    traffic to NULL?

    Thanks,
    Scott<-
     
    Scott Townsend, Apr 24, 2006
    #1
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  2. Scott Townsend

    Merv Guest

    correct
     
    Merv, Apr 24, 2006
    #2
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  3. Scott Townsend

    java321 Guest

    The purpose is to prevent routing loops.

    Here is an example
    http://www.cisco.com/en/US/tech/tk364/technologies_tech_note09186a00801c9a6e.shtml.

    Good Luck

    "Scott Townsend" <scott-i@.-N0-SPAMplease.enm.com> wrote in message
    news:eek:n83g.19574$...
    > We received a Router from an ISP and they have the Following Line in it.
    >
    > ip route A.B.C.0 255.255.255.0 Null0 254 permanent
    >
    > Where the local Ethernet Interface is: A.B.C.1 255.255.255.0
    >
    > What is the Purpose of this? If the Ethernet interface is Down, route all
    > traffic to NULL?
    >
    > Thanks,
    > Scott<-
    >
     
    java321, Apr 25, 2006
    #3
  4. Scott Townsend

    Mooron Guest

    Scott Townsend wrote:
    > We received a Router from an ISP and they have the Following Line in it.
    >
    > ip route A.B.C.0 255.255.255.0 Null0 254 permanent
    >
    > Where the local Ethernet Interface is: A.B.C.1 255.255.255.0
    >
    > What is the Purpose of this? If the Ethernet interface is Down, route all
    > traffic to NULL?
    >
    > Thanks,
    > Scott<-



    Also note the high metric of 254 which makes it the
    route of "last resort." A directly connected network
    has a metric of 0. Under normal cirucmastances,
    when the Ethernet is up, the route does nothing.

    It prevents bouncing of packets between you and
    your ISP when the Ethernet interface is down.

    - Mooron
     
    Mooron, Apr 25, 2006
    #4
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