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  • 1.  OSPF Multi-area Routing

    Posted 01-18-2020 04:48

    I have a question: 


    If the R2-R4 link fails, which way will traffic route from R1 to R4? I am thinking it will follow the lwoest metric, but as it is across areas, is it correct to go R1 - R2- R3 -R4? 




    Screenshot 2020-01-18 at 12.45.33.png


  • 2.  RE: OSPF Multi-area Routing

    Posted 01-18-2020 08:06

    There is too less information in the exhibit to answer this for sure. However, if the links R1 - R2 - R3 - R4 are all inside area 0, then the packets will go this way, as the traffic will not leave area 0 to transit another area to go back to area 0 again.

  • 3.  RE: OSPF Multi-area Routing
    Best Answer

    Posted 01-18-2020 20:26



    @NetworkMan23 wrote:

    is it correct to go R1 - R2- R3 -R4? 



    No. If this is pure IP forwarding (no MPLS and no tunnels of any sort: GRE, IPIP, IPSec etc) then when packet destined to R4 hits R2, then R2 has 2 choice routes:

    - INTRA area 10 route from R4 via R5

    - INTER area 0 route from R3

    According to RFC 2328 section 11, INTRA area route is preferred and R2 will send this packet to R5 and R5 will forward to R4.






  • 4.  RE: OSPF Multi-area Routing

    Posted 01-18-2020 21:08

    Intra-area routes are preferred over inter-area routes regarless of the metric. If you wanted traffic going to R4 to be sent via R3 when the link R2<=>R4 fails, you can configure multi-area adjancency between R2 and R3 as shown:

    multi-area adjacency.png 

    protocols ospf {

    area {

       interface ge-0/0/0.0;


    area {

       interface ge-0/0/0.0 {