ospf dual link and load balancing

Unanswered Question
Aug 2nd, 2008
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I have two site with distance of 10 km (sea between).

I use a primary link with BR350 (wifi bridge) and I have installed a redudancy link with adsl and DMVPN, the redudancy is provide by OSPF routing.

I use on main site a 4500 and 1811 (dmvpn), remote site 3550 (L3) and 1811 (dmvpn)

The link between sites use a vlan with interconnection network (for routing)

The problem is that the primary link (wifi bridge) sometimes lost the communication during 30 seconds, minuts or hours , problem with high boat in the bay (it's not a joke)

And in this case the ospf routing need 35 seconds to use the second link. but as the lost of the primary link sometime is few minuts, my routing is flapping, but it's normal.

Then I migrate to a second architecture with an OSPF cost equal.

It works, If I use traceroute I use sometime the primary link or primary , depend of source and destination IP addresses

I have configured the opsf maximum-path as 2 .

The problem is the same when one of links is lost the ospf need 35 seconds for adjacency. and all my trafic is lost during this phase.

My questions is how can I optimize the time to minimize the lost of packet. Do I need to use a lower ospf timer. use other routing ptotocol like eigrp, mixed dynamic routing and static

Optimize the load balancing on switch (3550 and 4500) with cef and destination per packet ?


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Marwan ALshawi Sun, 08/03/2008 - 02:36
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what u can do is

add bgp to ur config

make each sate with its one AS

lets say site one AS 10 and site two AS 20

and make the updat source of the EBGP peering between sites as the loop back addres for load balancing

and advertise the subnets between the two peers and in each router advertise the loopback address subnet

also use the following command for bgp loadbalncing


use the following link but consider only first example which will apply to ur case


follow it and should work better than before


good luck

Please if helpful Rate

Giuseppe Larosa Sun, 08/03/2008 - 02:53
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Hello Eric,

I would use reduced OSPF timers.

Verify if your IOS supports sub-second hello timer (this may be not applicable if you have high delay on the radio link).

ip ospf hello-interval 2

ip ospf dead-interval 8

or if applicable (verify delay and jitter on radio link)

ip ospf dead-interval {seconds |

minimal hello-multiplier multiplier}

Interface subcommand; defines the dead interval, or

optionally the minimal dead interval of 1 second.

just remember that timers must match in order to build successful OSPF adjacencies.

I wouldn't introduce other routing protocols all of them would face similar problems.

One feature that could help is BFD = bidirectional forwarding detection but again I don't know if it can work on the radio link and if it is supported on the IOS versions of your devices.

Hope to help



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