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New Member

Influence route in OSPF intra-area

Hi all,

I would like to know if it is possible to influence the traffic for a network to take one next hop if I have 2 routes with the same cost in OSPF? in a BMA environment.

R10#sh ip route  1.1.1.1

Routing entry for 1.1.1.1/32

  Known via "ospf 1", distance 110, metric 21, type intra area

  Last update from 10.10.10.2 on FastEthernet0/0, 00:40:09 ago

  Routing Descriptor Blocks:

  * 10.10.10.3, from 1.1.1.1, 00:40:09 ago, via FastEthernet0/0

      Route metric is 21, traffic share count is 1

    10.10.10.2, from 1.1.1.1, 00:40:09 ago, via FastEthernet0/0

      Route metric is 21, traffic share count is 1

I want to send the traffic to 1.1.1.1 through 10.10.10.2 and keep 10.10.10.3 as a backup.

They are Intra Area routes and both neighbors are learned by the same interface BMA.

R10#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

20.20.20.2        1   FULL/BDR        00:00:32    10.10.10.2      FastEthernet0/0

30.30.30.2        1   FULL/DR         00:00:38    10.10.10.3      FastEthernet0/0

I tried to change the metric with distrubute and a route map but no luck

any ideas?

Please  let me know if you need more details.


Everyone's tags (1)
1 ACCEPTED SOLUTION

Accepted Solutions

Re: Influence route in OSPF intra-area

Hi Omar,

you could change the network type to "point-to-multipoint non-broadcast".

A very interesting option especially for this type is that you can assign cost on a per-neighbor basis on a multiaccess interface:

(config-rtr)# neighbor [cost <1-65535>]

Optionally, you may want to change the timers (default: 30/120s).

Compared to Broadcast network type, Point-to-Multipoint Non-Broadcast

  • sends unicast hellos to every neighbor
  • transmits more OSPF traffic (no DR)
  • is less efficient in LSBD representation
  • installs host-routes for every router (for the spoke's reachability in frame-relay hub & spoke topologies)

However, if you have only 3-4 routers in the subnet, the advantages of Broadcast over Point-to-Multipoint shouldn't keep you from using that network type if you want to be able to influence the forwarding paths in a multiaccess network. I've already done this in production networks to overcome undesired adjacencies in a VPLS and implement backup-paths as well.

HTH

Rolf

7 REPLIES
New Member

Influence route in OSPF intra-area

Hi,

increase the cost of the connected neighbour router interface, at which IP 10.10.10.3 is configured using (ip ospf cost "value") at interface configuration mode.

Thanks

Shashi

Re: Influence route in OSPF intra-area

Hi Omar,

you could change the network type to "point-to-multipoint non-broadcast".

A very interesting option especially for this type is that you can assign cost on a per-neighbor basis on a multiaccess interface:

(config-rtr)# neighbor [cost <1-65535>]

Optionally, you may want to change the timers (default: 30/120s).

Compared to Broadcast network type, Point-to-Multipoint Non-Broadcast

  • sends unicast hellos to every neighbor
  • transmits more OSPF traffic (no DR)
  • is less efficient in LSBD representation
  • installs host-routes for every router (for the spoke's reachability in frame-relay hub & spoke topologies)

However, if you have only 3-4 routers in the subnet, the advantages of Broadcast over Point-to-Multipoint shouldn't keep you from using that network type if you want to be able to influence the forwarding paths in a multiaccess network. I've already done this in production networks to overcome undesired adjacencies in a VPLS and implement backup-paths as well.

HTH

Rolf

New Member

Influence route in OSPF intra-area

Thank you Rolf your solution worked for me to influce a path for an especific neighbor as next hop.

Thank you ALL I appreciate your comments

Silver

Influence route in OSPF intra-area

Change the cost. Draw a topology and provide more information if you want a more detailed answer. Remember that cost is calculated inbound.

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
Super Bronze

Re: Influence route in OSPF intra-area

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Posting

Besides Rolf's solution, another option might be to adjust interface cost, or interface costs, on one of either of the two adjacent (common network) routers.  As OSPF intra-area costs are cumulative, this make the two paths costs unequal.

New Member

Re: Influence route in OSPF intra-area

just change the cost and you are done one path will be backup and one active

if you want exact point where to give cost share your diagram

Sent from Cisco Technical Support iPhone App

Regards Waqas Younas CCIEx2 #27815 (Routing and Switching) (Service Provider) Contact for Online Training
New Member

Influence route in OSPF intra-area

Thank you Rolf your solution worked for me to influce a path for an especific neighbor as next hop.

Thank you ALL I appreciate your comments

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