OSPF All in One Lab---(DR,Stub,NSSA, FRR) Highlighted

Created: Mar 2, 2015 17:44:22Latest reply: Sep 30, 2018 18:52:15 2937 3 0 0

Section III: DR & BDR

<RouterB>display ospf peer

 

          OSPF Process 1 with Router ID 2.2.2.2

                    Neighbors

 

 Area 0.0.0.0 interface 10.1.1.2(GigabitEthernet0/0/0)'s neighbors

 Router ID: 1.1.1.1          Address: 10.1.1.1       

   State: Full  Mode:Nbr is  Slave  Priority: 1

   DR: 10.1.1.2  BDR: 10.1.1.1  MTU: 0   

   Dead timer due in 35  sec

   Retrans timer interval: 5

   Neighbor is up for 00:07:05    

   Authentication Sequence: [ 0 ]

This one is easy, if the priority is the same, the one with bigger IP address will be selected as DR. What’s the use of DR? It’s just like a class head in an area to handle routes in an area. We can see in area 1 RouterB’s BDR.

[RouterB]display ospf interface

 

          OSPF Process 1 with Router ID 2.2.2.2

                    Interfaces

 

 Area: 0.0.0.0          (MPLS TE not enabled)

 IP Address      Type         State    Cost    Pri   DR              BDR

 10.1.1.2        Broadcast    DR       1       1     10.1.1.2        10.1.1.1

 2.2.2.2         P2P          P-2-P    0       1     0.0.0.0         0.0.0.0

 

 Area: 0.0.0.1          (MPLS TE not enabled)

 IP Address      Type         State    Cost    Pri   DR              BDR

 10.2.1.1        Broadcast    BDR      1       2     10.2.1.2        10.2.1.1

 

 Area: 0.0.0.2          (MPLS TE not enabled)

 IP Address      Type         State    Cost    Pri   DR              BDR

 10.3.1.1        Broadcast    BDR      1       1     10.3.1.2        10.3.1.1

If we want RouterB to be DR in area 1, we can use [RouterB-GigabitEthernet0/0/1]ospf dr-priority 2, but we need to use reset ospf 1 process to make it effective. Now the DR is 10.2.1.1 instead.

Area: 0.0.0.1          (MPLS TE not enabled)

 IP Address      Type         State    Cost    Pri   DR              BDR

 10.2.1.1        Broadcast    DR       1       2     10.2.1.1        10.2.1.2

Section IV Stub

If we have a check of routing table of RouterE, we can see it’s complicated as below:

<RouterE>display ospf routing

 

          OSPF Process 1 with Router ID 5.5.5.5

                     Routing Tables

 

 Routing for Network

 Destination        Cost  Type       NextHop         AdvRouter       Area

 5.5.5.5/32         0     Stub       5.5.5.5         5.5.5.5         0.0.0.3

 10.4.1.0/24        1     Transit    10.4.1.2        5.5.5.5         0.0.0.3

 1.1.1.1/32         3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 2.2.2.2/32         2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 4.4.4.4/32         1     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.1.1.0/24        3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.2.1.0/24        2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.3.1.0/24        3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 

 Total Nets: 8 

 Intra Area: 2  Inter Area: 6  ASE: 0  NSSA: 0 Is it possible to reduce it? Yeah, of course, everything is invented with purpose. Stub area is invented and we can configure area 3 as stub area.

[RouterE]display ospf routing

 

          OSPF Process 1 with Router ID 5.5.5.5

                     Routing Tables

 

 Routing for Network

 Destination        Cost  Type       NextHop         AdvRouter       Area

 5.5.5.5/32         0     Stub       5.5.5.5         5.5.5.5         0.0.0.3

 10.4.1.0/24        1     Transit    10.4.1.2        5.5.5.5         0.0.0.3

 0.0.0.0/0          2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 1.1.1.1/32         3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 2.2.2.2/32         2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 4.4.4.4/32         1     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.1.1.0/24        3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.2.1.0/24        2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 10.3.1.0/24        3     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 

 Total Nets: 9 

 Intra Area: 2  Inter Area: 7  ASE: 0  NSSA: 0

     What’s the difference? We can see now that there is a default route instead. All routes outside of AS will be vanished, only we don’t have another AS in this OSPF example. If we configure the stub area as totally stub area, we can reduce inter-area route instead.

[RouterE-ospf-1-area-0.0.0.3]stub no-summary

[RouterE]display ospf routing

 

          OSPF Process 1 with Router ID 5.5.5.5

                     Routing Tables

 

 Routing for Network

 Destination        Cost  Type       NextHop         AdvRouter       Area

 5.5.5.5/32         0     Stub       5.5.5.5         5.5.5.5         0.0.0.3

 10.4.1.0/24        1     Transit    10.4.1.2        5.5.5.5         0.0.0.3

 0.0.0.0/0          2     Inter-area 10.4.1.1        4.4.4.4         0.0.0.3

 

 Total Nets: 3 

 Intra Area: 2  Inter Area: 1  ASE: 0  NSSA: 0

We can see that inter area routes are all vanished to make a cleaner routing table for RouterE. The area 3 is now a totally stub area.

 [RouterE-ospf-1] import-route static type 1

 

Section V NSSA

Sometimes, we’d like to import AS external routes, so we need NSSA instead. Let’s configure area 2 as NSSA. We can see RouterB’s routing table as below:

Routing for ASEs

 Destination        Cost      Type       Tag         NextHop         AdvRouter

 200.0.0.0/8        2         Type1      1           10.3.1.2        3.3.3.3

After configuration, it becomes:

Routing for NSSAs

 Destination        Cost      Type       Tag         NextHop         AdvRouter

 200.0.0.0/8        2         Type1      1           10.3.1.2        3.3.3.3

With no-summary, the routing table of RouterC is clean:

[RouterC]display ospf routing

 

     OSPF Process 1 with Router ID 3.3.3.3

         Routing Tables

 

 Routing for Network

 Destination        Cost  Type       NextHop         AdvRouter       Area

 10.3.1.0/24        1     Transit    10.3.1.2        3.3.3.3         0.0.0.2

 0.0.0.0/0          2     Inter-area 10.3.1.1        2.2.2.2         0.0.0.2

 

 Total Nets: 2 

 Intra Area: 1  Inter Area: 1  ASE: 0  NSSA: 0

 

Section VI FRR

If we want to test FRR, we need to add an extra link as below:

From routing table of RouterA, we can see there are two ways to 10.3.1.0.

       10.3.1.0/24  OSPF    10   2          D   10.1.1.2        GigabitEthernet0/0/0

                    OSPF    10   2        D   10.5.1.2        GigabitEthernet0/0/1

We can configure GE0/0/1 OSPF cost as 10 [RouterA-GigabitEthernet0/0/1]ospf cost 10. Then the remaining route is

10.3.1.0/24   2     Inter-area 10.1.1.2        2.2.2.2         0.0.0.0

So we already make GE0/0/0 primary link while GE0/0/1 backup link. If we disable GE0/0/0, the routing table of RouterA is as below:

Routing for Network

 Destination        Cost  Type       NextHop         AdvRouter       Area

 1.1.1.1/32         0     Stub       1.1.1.1         1.1.1.1         0.0.0.0

 10.1.1.0/24        1     Stub       10.1.1.1        1.1.1.1         0.0.0.0

 10.5.1.0/24        10    Transit    10.5.1.1        1.1.1.1         0.0.0.0

 10.3.1.0/24        11    Inter-area 10.5.1.2        3.3.3.3         0.0.0.0

 

 Routing for ASEs

 Destination        Cost      Type       Tag         NextHop         AdvRouter

 200.0.0.0/8        11        Type1      1           10.5.1.2        3.3.3.3

   You can see the Nexthop is 10.5.1.2, but it takes time to reroute, which will have network interruption, so we invent FRR to resolve this. [RouterA-ospf-1]frr

Now we disable GE0/0/0,the nexthop will become 10.5.1.2 immediately, nice!!

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user_2790689     Created Mar 4, 2015 10:50:03 Helpful(0) Helpful(0)

Thank you.
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user_113229  Visitor   Created Mar 4, 2015 17:40:59 Helpful(0) Helpful(0)

Reply 2 #

Thanks for your appreciation.O(∩_∩)O~
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faysalji  Visitor   Created Sep 30, 2018 18:52:15 Helpful(0) Helpful(0)

Thanks dear for sharing
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