What is the default precedence: local-route, static-route,OSPF-route?

Discussion in 'Cisco' started by ilan.berco@gmail.com, Aug 4, 2008.

  1. Guest

    Hi

    What is the default precedence: local-route, static-route, OSPF-route?
    Based on ipForwardProto (2/1/13)
    Need a reference (RFC?)

    Thanks in advance
    Ilan
     
    , Aug 4, 2008
    #1
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  2. Uli Link Guest

    Re: What is the default precedence: local-route, static-route, OSPF-route?

    schrieb:
    > Hi
    >
    > What is the default precedence: local-route, static-route, OSPF-route?
    > Based on ipForwardProto (2/1/13)
    > Need a reference (RFC?)


    The metric of the route

    --
    Uli
     
    Uli Link, Aug 4, 2008
    #2
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  3. Guest

    On 4 ×וגוסט, 10:24, Uli Link <>
    wrote:
    > schrieb:
    >
    > > Hi

    >
    > > What is the default precedence: local-route, static-route, OSPF-route?
    > > Based on ipForwardProto (2/1/13)
    > > Need a reference (RFC?)

    >
    > The metric of the route
    >
    > --
    > Uli


    Thanks.
    In that case, the direct-route will allways have priority (since it's
    cost is 0).
    Any reference please?
    Ilan
     
    , Aug 4, 2008
    #3
  4. Merv Guest

    administrative distance of the routes in question

    0 connected routes

    1 static routes

    110 OSPF routes


    Thus connected preferred over static preferred over OSPF
     
    Merv, Aug 4, 2008
    #4
  5. Guest

    On 4 ×וגוסט, 15:56, Merv <> wrote:
    > administrative distance of the routes in question
    >
    >    0   connected routes
    >
    >    1   static routes
    >
    > 110 OSPF routes
    >
    > Thus connected preferred over static preferred over OSPF


    Thanks. So "administrative distance" is prior to metric?
    Does the command: "Precedence = ospf rip static" overrides the default
    "administrative distance"?
     
    , Aug 4, 2008
    #5
  6. Merv Guest

    On Aug 4, 9:36 am, wrote:
    > On 4 ×וגוסט, 15:56, Merv <merv.hr...@rogers..com> wrote:
    >
    > > administrative distance of the routes in question

    >
    > > 0 connected routes

    >
    > > 1 static routes

    >
    > > 110 OSPF routes

    >
    > > Thus connected preferred over static preferred over OSPF

    >
    > Thanks. So "administrative distance" is prior to metric?
    > Does the command: "Precedence = ospf rip static" overrides the default
    > "administrative distance"?




    Are you referring to IOS routing or some other Cisco product ?

    AFAIK there is no IOS command "Precedence = ospf rip static"

    In IOS, administrative distance is the FIRST tie breaker for route
    selection
     
    Merv, Aug 4, 2008
    #6
  7. Stephen Guest

    Re: What is the default precedence: local-route, static-route, OSPF-route?

    On Mon, 4 Aug 2008 01:32:14 -0700 (PDT), wrote:

    >On 4 ??????, 10:24, Uli Link <>
    >wrote:
    >> schrieb:
    >>
    >> > Hi

    >>
    >> > What is the default precedence: local-route, static-route, OSPF-route?
    >> > Based on ipForwardProto (2/1/13)
    >> > Need a reference (RFC?)

    >>
    >> The metric of the route
    >>
    >> --
    >> Uli

    >
    >Thanks.
    >In that case, the direct-route will allways have priority (since it's
    >cost is 0).
    >Any reference please?


    2nd google search for "cisco.com routing administrative distance"
    1st hit...
    http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094195.shtml

    >Ilan

    --
    Regards

    - replace xyz with ntl
     
    Stephen, Aug 4, 2008
    #7
  8. John Agosta Guest

    Re: What is the default precedence: local-route, static-route, OSPF-route?

    <> wrote in message
    news:...
    > Hi
    >
    > What is the default precedence: local-route, static-route, OSPF-route?
    > Based on ipForwardProto (2/1/13)
    > Need a reference (RFC?)
    >
    > Thanks in advance
    > Ilan




    I assume you are looking for the "route selection process"..........

    1 - Follow the route with the longest match. (prefix length)



    RIP 10.1.1.0 via s1

    OSPF 10.1.0.0 via s2

    Static 10.0.0.0 via s3

    EIGRP 10.1.0.0 via s4



    ping 10.1.1.1





    Where does the router send the ping?

    I will send the ping via s1.







    2 - Assuming there were multiple possibilities, and the match/mask
    length was the same for all:



    RIP 10.1.0.0 via s1

    OSPF 10.1.0.0 via s2

    Static 10.1.0.0 via s3

    EIGRP 10.1.0.0 via s4





    Static Route Wins.



    a - ip route 10.1.0.0 255.255.0.0 serial 3 (points to a physical
    interface)



    b - ip route 10.1.0.0 255.255.0.0 12.12.12.12 (points to a
    next-hop-address)







    3 - if there are no static routes:



    RIP 10.1.0.0 via s1

    OSPF 10.1.0.0 via s2

    ISIS 10.1.0.0 via s3

    EIGRP 10.1.0.0 via s4



    The router will take the advice of a dynamic routing protocol.



    The order of preference is:



    Prot AD

    EIGRP 90

    OSPF 110

    ISIS 115

    RIP 120



    We prefer routing protocols with a lower "administrative distance"







    4 - If there's no dynamic route, then follow a default route:



    a - ip route 0.0.0.0 0.0.0.0 serial 3 (points to a physical
    interface)



    b - ip route 0.0.0.0 0.0.0.0 12.12.12.12 (points to a
    next-hop-address)



    Default routes are also known as "last resort" routes. In the above,
    12.12.12.12

    would be the "gateway of last resort."





    5 - None of the above ? Throw the packet away. You can't deal with
    it.
     
    John Agosta, Aug 4, 2008
    #8
  9. Merv Guest

    For routes that have the same mask, administrative distance is the
    first parameter used to select the route which will be inserted into
    the RIB ( routing table)
     
    Merv, Aug 5, 2008
    #9
  10. Scott Perry Guest

    Re: What is the default precedence: local-route, static-route, OSPF-route?

    This post has the following sections:
    * Original Question
    * Clarification
    * Short Answer
    * Full Answer
    * Routing Example #1
    * Routing Example #2
    * Routing Example #3
    * Routing Example #4


    QUESTION:

    > What is the default precedence: local-route, static-route,

    OSPF-route?
    > Based on ipForwardProto (2/1/13)
    > Need a reference (RFC?)



    CLARIFICATION:

    ipForwardProto is an SNMP MIB. Let's not pay very much attention to the
    results of SNMP values and stick with the selection of routes from your
    question.
    The revisied question that I will answer is, "What is the selection process
    for routing?"


    SHORT ANSWER:

    For Cisco routers (not other vendor products), the default administrative
    distances, when not otherwise altered, are as follows:
    0 - Directly connected
    1 - Static route
    5 - EIGRP summary route
    20 - External BGP
    90 - Internal EIGRP
    100 - IGRP
    110 - OSPF
    115 - IS-IS
    120 - RIP
    140 - EGP
    160 - ODR
    170 - External EIGRP
    200 - Internal BGP
    255 - Unknown
    If more than one routing entry exists for the same network, the one with the
    lower administrative distance is used. Therefore, using the protocols from
    your original question, this is the selection order:
    1) local routes
    2) static routes
    3) OSPF routes


    FULL ANSWER:

    The most specific routing entries are selected first, no matter the source
    of the routing information. If more then one entry for the exact same route
    is available, the one with the lowest administrative distance value is
    selected. If more than one entry for the exact same route is available with
    the same administrative distance, the one with the better metric is
    selected.
    1) Most specific route entry, no matter the method which is is learned
    2) Lowest administrative distance of the method which the route is learned
    (routing protocol)
    3) Best metric of the available routes within that method (routing
    protocol)

    The exception to this is when the administrative distance is changed.
    Static routes normally have an administrative distance of 1. This makes them
    less preferable than routing information from the interface configuraiton
    but more preferable than routing information from dynamic routing protocols
    like EIGRP and OSPF. This administrative distance of a static route can be
    changed.
    This is a normal static route which will have an administrative distance of
    1:
    ip route 10.0.0.0 255.255.255.0 192.168.1.1
    This is a modified static route which will have an administrative distance
    of 220:
    ip route 10.0.0.0 255.255.255.0 192.168.1.1 220
    These are sometimes referred to as "floating static routes" because other
    routing methods are more likely to be used.


    EXAMPLE #1:

    A router with interfaces Serial0/0, Serial0/1, and FastEthernet0/0 is
    running EIGRP and OSPF while also having some static routes.
    The results of "show ip route" contain these entries:
    D 10.1.0.0/16 [90/180000] via 192.168.1.1, 2w3d, Serial0/0
    O 10.1.0.0/16 [110/65] via 192.168.2.1, 2w3d, Serial0/1
    S 10.1.0.0/16 [1/0] via 192.168.1.1
    S 10.1.0.0/16 [20/0] via 192.168.2.1

    If traffic is being routed to 10.1.1.1, it will go to 192.168.1.1.

    The IP address 10.1.1.1 matches all four of the routing table entries
    equally with no one entry being more specific than the other. Therefore
    administrative distance is used and the static route with an administrative
    distance of 1 is used. No other routing table entries have the same
    administrative distance so the routing metric is not a factor.


    EXAMPLE #2:

    A router with interfaces Serial0/0, Serial0/1, and FastEthernet0/0 is
    running EIGRP and OSPF while also having some static routes.
    The results of "show ip route" contain these entries:
    D 10.1.0.0/16 [90/180000] via 192.168.1.1, 2w3d, Serial0/0
    O 10.1.0.0/16 [110/65] via 192.168.2.1, 2w3d, Serial0/1
    S 10.1.0.0/16 [1/0] via 192.168.1.1
    S 10.1.1.0/24 [20/0] via 192.168.2.1

    If traffic is being routed to 10.1.1.1, it will go to 192.168.2.1.

    The IP address 10.1.1.1 does match all four of the routing table entries but
    the routing table entry 10.1.1.0/24 is more exact than the other entries
    using 10.1.0.0/16. Administrative distance is not considered because this
    one route matched more accurately. Metric is not considered because this
    one route matched more accurately.


    EXAMPLE #3:

    A router with interfaces Serial0/0, Serial0/1, and FastEthernet0/0 is
    running EIGRP and OSPF while also having some static routes.
    The results of "show ip route" contain these entries:
    D 10.1.0.0/16 [90/180000] via 192.168.1.1, 2w3d, Serial0/0
    O 10.1.0.0/16 [110/65] via 192.168.2.1, 2w3d, Serial0/1
    S 10.1.0.0/16 [100/0] via 192.168.1.1
    Where will traffic to 10.1.1.1 normally be routed?
    If the EIGRP learned route is lost, where will traffic to 10.1.1.1 be
    routed?

    If traffic is being routed to 10.1.1.1, it will go to 192.168.1.1.
    If the EIGRP learned route is lost, traffic to 10.1.1.1 will go to
    192.168.1.1.

    The IP address 10.1.1.1 matches all three of the routing table entries
    equally including the two entries which would remain after the EIGRP routing
    table entry is lost. The administrative distance of EIGRP, 90, would be the
    first choice but the modified administrative distance of the static route,
    100, makes a second choice before considering routes from OSPF with an
    administrative distance of 110. No other routing table entries have the
    same administrative distance so the routing metric is not a factor.
    The EIGRP route to 192.168.1.1 is used first.
    The static route to 192.168.1.1 is used second.
    The OSPF route to 192.168.2.1 is used third.


    EXAMPLE #4:

    A router with interfaces FastEthernet0/0 and FastEthernet0/1 has some static
    routes.
    The results of "show ip route" contain these entries:
    S* 0.0.0.0/0 [1/0] via 192.168.10.1
    S 10.0.0.0/8 [1/0] via 192.168.10.2
    S 10.0.0.0/16 [1/0] via 192.168.10.3
    S 10.0.0.0/24 [20/0] via 192.168.10.4
    If traffic is being routed to 10.0.1.1, it will go to 192.168.10.3.

    The IP address 10.0.1.1 matches three of the four routing table entries.
    The routing table entry for 10.0.0.0/16 is the most exact of the three and
    is the best match. Therefore administrative distance is used and the static
    route with an administrative distance of 1 is used. Administrative distance
    is not considered because one route matched with the most accuracy. Metric
    is not considered because this one route matched with the most accuracy.


    REFERENCE:

    There is not an RFC for this route selection process because this is
    specific to Cisco devices. Other router manufacturers will very likely not
    have IGRP and EIGRP so the administrative distance table cannot apply to
    them.
    The methods by which dynamic routing protocols determine their own internal
    metrics are available in RFCs for each specific routing protocol.

    You may want to reference books and materials regarding the Cisco CCNP exam
    642-901, "Building Scalable Cisco Internetworks". They cover routing
    protocol metrics and Cisco routing administrative distances.


    I hope that answered any questions on the subject.

    -----
    Scott Perry
    Indianapolis, IN
    -----

    <> wrote in message
    news:...
    > Hi
    >
    > What is the default precedence: local-route, static-route, OSPF-route?
    > Based on ipForwardProto (2/1/13)
    > Need a reference (RFC?)
    >
    > Thanks in advance
    > Ilan
     
    Scott Perry, Aug 7, 2008
    #10
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