Route tagging and Prefering the path

HI,

Can advice the other methods we could use for R5 to prefer the path from BB1 and BB3.

I tried to tag the routers from BBs and tried to set nex-hop as R1 and R2 for those tagged Prefixes, but couldnt achieve the result.

Is that a correct way ??

 

Thanks

rYs

Comments

  • Hi rYs,

    First of all, you need to make sure that the route gets into the BGP table and it's eligibile for use. This is true if some conditions are met (Why routers ignore paths section).

    I would recommend going through the BGP bestpath selection algorithm for more info on this topic :

    http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

    After the prefix is inserted into the BGP table, then path manipulation comes into play, following the algorithm described in the page above outlined.

    If you need anything else, please try to post a more specific question and I will try to help.

     


  • HI,

    Thanks for your response,

    Its on the Section 2.2 from Vol 2 Lab 3.

    The task asks to perform during the redistribution, before coming to BGP.
    It asks for R5 to prefer routes to BB1 via R1 and prefixes to BB3 via R2 while redistributing RIP routes into EIGRP at R6.

    In the WB, solution, is adjusting the metrics of tagged prefixes from BB1 and BB3 at R1 and R3.

    Apart from this, can advise other solutions??

    Thanks




    On 4 Jun, 2014, at 5:32 pm, ciprian_s <[email protected]> wrote:

    Hi rYs,

    First of all, you need to make sure that the route gets into the BGP table and it's eligibile for use. This is true if some conditions are met (Why routers ignore paths section).

    I would recommend going through the BGP bestpath selection algorithm for more info on this topic :

    http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

    After the prefix is inserted into the BGP table, then path manipulation comes into play, following the algorithm described in the page above outlined.

    If you need anything else, please try to post a more specific question and I will try to help.

     



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  • Hi,

    To fully understand this design I would suggest to ask yourself this question : "What are the decision points in this diagram for the requirements to be met ?".

    What I mean by that is something like the following : 

    - R5 will choose one path over the other based on cost (OSPF best path algorithm for same LSA type, in this case LSA type5 )

    - The path can be influenced on R1 and R2, in this manner R1 sets lower metric for routes originated in BB1 and R2 sets lower metric for routes originated in BB3

    - How can I make the distinction between the routes originated in the two BB routers ?

      In the solution guide route tagging has been used for prefix matching because it's also a scalable solution. So this solution applies for any further prefixes that will be originated on BB1 or BB3; think of it as a dynamic solution.

    If this is not needed or requested in the lab, you could match the routes on R1originated on BB1 in a prefix-list and set a metric of 1 and match the routes originated on BB3 in a prefix-list on R2 and in the same way set a lower metric here, when doing the redistribution to OSPF. But again, if any other prefix is originated on the BB routers prefix-list manipulation will be needed on R1 and/or R2.

    Example : 

    R1 :

    route-map EIGRP->OSPF permit 10

    match ip address prefix-list PFL_FROM_BB1

    set metric 1

    route-map EIGRP->OSPF permit 20  >> this is needed to ensure that the other prefixes, not originated on BB1 get passed into OSPF also

     

    Does this answer your question ?

     

     

  • Hi

    Thanks for the explanation.

    I clearly understand the solution provided in WB.

    Is it possible to use R5 as decision point and set the next hop to R1 and R2 interfaces for those prefixes.

    I would like to know an alternate solution.

    Correct me if we cannot provide a solution I mentioned above.

    Thanks

    On 4 Jun 2014 23:22, "ciprian_s" <[email protected]> wrote:

    Hi,

    To fully understand this design I would suggest to ask yourself this question : "What are the decision points in this diagram for the requirements to be met ?".

    What I mean by that is something like the following : 

    - R5 will choose one path over the other based on cost (OSPF best path algorithm for same LSA type, in this case LSA type5 )

    - The path can be influenced on R1 and R2, in this manner R1 sets lower metric for routes originated in BB1 and R2 sets lower metric for routes originated in BB3

    - How can I make the distinction between the routes originated in the two BB routers ?

      In the solution guide route tagging has been used for prefix matching because it's also a scalable solution. So this solution applies for any further prefixes that will be originated on BB1 or BB3; think of it as a dynamic solution.

    If this is not needed or requested in the lab, you could match the routes, for example, originated on BB1 in a prefix-list and set a metric of 1 and match the routes originated on BB3 in a prefix-list on R2 and in the same way set a lower metric here, when doing the redistribution to OSPF. But again, if any other prefix is originated on the BB routers prefix-list manipulation will be needed on R1 and/or R2.

    Example : 

    R1 :

    route-map EIGRP->OSPF permit 10

    match ip address prefix-list PFL_FROM_BB1

    set metric 1

    route-map EIGRP->OSPF permit 20  >> this is needed to ensure that the other prefixes, not originated on BB1 get passed into OSPF also

     

    Does this answer your question ?

     

     





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