16 comments on “OSPF : Challenge backup (easy)

  • Hi Lorenzo,

    Difficult to do this on the same LAN (172.16.0.0/24). OSPF cost affects on receive. So if you make ‘ip ospf cost XX’ on port, it will affect all costs…

    Regards,
    Christophe

  • You will influence the return path, not the forward path.

    You will have :

    R1#traceroute 99.99.99.0

    Type escape sequence to abort.
    Tracing the route to 99.99.99.0

    1 172.16.0.3 288 msec
    172.16.0.2 400 msec
    172.16.0.3 1124 msec
    2 10.24.0.4 636 msec
    10.34.0.4 260 msec
    10.24.0.4 436 msec
    R1#

    Regards,
    Christophe

  • Mhh…you are right.
    If R1 is high end router, you can run OSPF LFA. Otherwise I have no idea 🙂

  • Create two different vlans (one for each router) with subinterfaces and the trath each one as different interface with different weigth.

    What do you think about that?

  • OSPF prefers Intra-Area routes over Inter-Area routes.

    So, what we can do… Put R4 and R3’s fastethernet interface on an other area. Area 1 for example. R4’s loopback still on area 0 :

    R4#sh run | inc interface (Fa|Lo)|_ip ospf
    interface Loopback0
    ip ospf 1 area 0
    interface FastEthernet0/0
    ip ospf 1 area 0
    interface FastEthernet0/1
    ip ospf 1 area 1

    And from R1 :
    R1#sh ip route ospf
    99.0.0.0/32 is subnetted, 1 subnets
    O 99.99.99.1 [110/21] via 172.16.0.2, 00:13:56, FastEthernet0/0
    10.0.0.0/24 is subnetted, 2 subnets
    O 10.24.0.0 [110/20] via 172.16.0.2, 00:18:25, FastEthernet0/0
    O IA 10.34.0.0 [110/20] via 172.16.0.3, 00:15:28, FastEthernet0/0

    R1#traceroute 99.99.99.1

    Type escape sequence to abort.
    Tracing the route to 99.99.99.1

    1 172.16.0.2 40 msec 28 msec 20 msec
    2 10.24.0.4 28 msec 36 msec 40 msec

    Am I right ?

    • You can do this way, but there is a solution to make prefer R2 in the same area (area 0).
      Have fun to fond the solution.

      Regards,
      Christophe

  • Changing the interfaces network type of 172.16.0.0/24 LAN to Point-to-Multipoint, so we can manually put a lower cost with the neighbor command to R2 ?

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