4.1 Alternate

I used tunnels (2 on R5 and 1 each on R1 and R2) instead of changing the network type on R5.  Creating the tunnels causes the neighbors to form over point to point links and that way there is no BDR on R2.  I thought this way a better solution than having a BDR on a spoke router.

R5

interface Tunnel15
 ip unnumbered Serial0/0.125
 tunnel source Serial0/0.125
 tunnel destination 173.1.125.1
!
interface Tunnel25
 ip unnumbered Serial0/0.125
 tunnel source Serial0/0.125
 tunnel destination 173.1.125.2

RSRack1R5#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
150.1.1.1         0   FULL/  -        00:00:32    173.1.125.1     Tunnel15
150.1.2.2         0   FULL/  -        00:00:34    173.1.125.2     Tunnel25

R1

interface Tunnel15
 ip unnumbered Serial0/0
 tunnel source Serial0/0
 tunnel destination 173.1.125.5

R2

interface Tunnel25
 ip unnumbered Serial0/0
 tunnel source Serial0/0
 tunnel destination 173.1.125.5

Comments

  • I also used an alternative method. I made R5 s0/0.125 a point-to-multipoint interface. Works great.

  • Actually I taket that back. Adjacencies will form and routing will work, but the DR election does obviously not work, only the 3 different broadcast - nonbroadcast combinations do DR negotiations.

    When configuring R5 as Multipoint it does not participate in DR election, so we get 2 separate DR segments where R1 becomes a DR and also R2 becomes a DR

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