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New Member

manipulate ospf routing

Hi all,


Basically we are having a Multicast setup.  both  A and B offices are being connected with STM-4 (622 Mbps) with IGP as OSPF. As of now everything is working well with this setup and no complaint .


Now since Primary link bandwidth is touching upto 622 Mbps  we are planning to send some traffic to backup STM-4 link

.

1) To send some vlan traffic always to backup STM-4 link here it is vlan 100 ( 10.20.6.0/24) what would be best way to do it.


Please find attached my network setup. 

Any suggestion would be highly appreciated. Pl reply


Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

manipulate ospf routing

Hi Bradford,

Since you have multiple vlans, I assume that you either have sub-interfaces on the router or each vlan is connected to a seperate physical interface. We could increase the cost both ways for a particular vlan for ospf and have them use the backup link. If possible plz do post configs for the devices for me to understand them better.

Rustom Billimoria

22 REPLIES
VIP Super Bronze

manipulate ospf routing

Hi,

Since the speed of both primary and backup links are the same , by default OSPF equity load balance the traffic for you.

HTH

New Member

manipulate ospf routing

Hi Reza,

Thanks for the reply.

Since we have defined  difference" cost" on both links in our case there is no load balance happening between links. The traffic willl flow to backup link only when there is a failure in primary link.

Now primary link is almost utilized i am planning to send some vlan traffic to backup link. is theref any way i can send the specific traffic to backup link. can i use distribute-list to manipulate ospf routing?

Thanks

manipulate ospf routing

New Member

manipulate ospf routing

Hi Dani,

I dont want to do loadbalancing between primary and backup links. I want the whole traffic except one vlan should be going always to Primary link. Since the primary link  is getting saturated i want to send some one vlan traffic always to backup link.  is there any way i can do it this with out disturbing the network.

Thanks... hope i made it clear now.

New Member

manipulate ospf routing

Can anyone pl respond...thanks

manipulate ospf routing

You could use a route-map to policy route some traffic to a specific next-hop IP address or interface.

New Member

manipulate ospf routing

Hi Brad,

Thanks for your reply.

Since i am running multicast service(ssm) between locations does this route map support multicast traffic to be sent out ?

New Member

manipulate ospf routing

Hi Bradford,

Since you have multiple vlans, I assume that you either have sub-interfaces on the router or each vlan is connected to a seperate physical interface. We could increase the cost both ways for a particular vlan for ospf and have them use the backup link. If possible plz do post configs for the devices for me to understand them better.

Rustom Billimoria

New Member

manipulate ospf routing

Hi Rustom,

By mistake i did click on the correct answer button next to u r comment. no how do i change it back ?

New Member

manipulate ospf routing

oh man!!!!

My first rating (that too by mistake) :-(

Maybe i can help you out to the end for exchange for the correct answer :-)

By the way route-maps d not match multicast traffic.. unless and until you match the destination address.

I'd suggest we manipute a certain Subnet being sent across by ospf to manipulate the path.

for example you have 4 subnets

10.0.0.0/24

10.0.1.0/24

10.0.2.0/24

10.0.3.0/24

all routes are being prefered over the primary path. how about we set a route-map to manipulate one subnet and increase its cost before sending it over to the other neighbor. that way the other side prefers the backup link. Do manipulate traffic both ways or you will end up with asymetric routing.

If you need an sample config, just ask and i will provide it to you.

Cheers!!!

Rustom Billimoria.

New Member

manipulate ospf routing

Hi Rustom,

Sorry for being late .

I hope you have understood my requirement correctly. if not please have a look at the diagram which i have attached along with the discussion.

I am going to add one more vlan 100 ( 10.20.6.0/24) to the existing setup and forward traffic( mainly Multicast-SSM traffic)  from this vlan exclusively to BACKUP STM 4 terminated in back up switch. at any point of time traffic from this vlan should be fall back to primary stm 4 link. when BACKUP STM 4 link gets down i may shut down this vlan interface manually.

As all routes are preffered over the primary STM 4 link whats the best way to achieve this requirement.  i dont have any control over B end devices. those devices are being managed by a( vendor )differnet team in other location .  So i have to do it requirement from A end which is my side.

Thanks for your time.

New Member

manipulate ospf routing

Gotcha!!!. thanks for the info man.. just keep checking the post for furthre updates..

New Member

Re: manipulate ospf routing

Hi Rustom,

I have not done the configuration .  ....could you suggest me the best way to do it?  any sample configs?

Thanks

New Member

manipulate ospf routing

Am already on it.. maybe a hour or so i'll be done.. just keep checking.

New Member

Re: manipulate ospf routing

Thanks will wait

New Member

Re: manipulate ospf routing

Hi Rustom,

Do u have any update on this ..thanks

Bronze

Re: manipulate ospf routing

How about changing the HSRP active Router for vlan 100 to the Backup-Router? Then increase the cost of the Etherchannel to at least 111 so that all vlan 100 traffic is routed over the backup line while all other vlans use the primary link.

Don't forget to do the same on the destination side or you'll witness asynchronous routing...

regards

Pille

New Member

Re: manipulate ospf routing

Hi Pille,

Thanks for your suggestions.

Since we dont have contol on the other end i dont think we can do this work around.  i need to find a best & suitable way to do this from my side.  Is there any other way through which we can send the vlan 100 traffic( Multicast SSM) to Backup link? do u see any more options?

New Member

manipulate ospf routing

Hi,

Sorry to be replying late. But it has been 2 days since I have been working with solutions for your network. Being a CCIE for routing switching, I had all the access to required equipment and hence had someone from my office setup equipment exactly as per your scenario. Even though chances of what you need to be achieving are bleek, I will publish result for what I have tried so far as to people who are willing to help you out can understand problems with the solution.

  • •1)      Initialy , I thought about manipulating metric for the prefix, but as I figure out that in a link state routing protocol, end to end visibility is important and hence, we at any point of time can change the link state database for 2 different routers. I means that all the routers need to have the same link state database. Hence the fisrt option of manipulating metric is lost.
  • •2)      Second I though about changing the administrative distance. I figured that maybe if we could change the AD of routes from 2 difference neighbours, the route with lower AD value would be preferred. :-P. Ok then I remember… blah…. Metric is preferred first, then the AD value.

So now I started to think out of best practises. Being a CCIE, it is important that we think out of the “BEST PRACTICE”fashion.

How about we have a static route with tracking via IP SLA on the backup  route device and redistribute it in ospf to the neighbour device with a lower metric. OK!!! . But it seems to have a problem.

OSPF will always prefer an intra-area route, then an inter-area route and lastly an external route. Hence even with a lower metric, the internal route across the primary link would be chosen.

Now I was in a fix, so we tried something else.

Like the above I did think about HSRP, but it will eventually follow the link which is preferred by OSPF. HSRP only will get information till the GATEways. They do not influence routing decisions. This decision is still OSPF.

And apart from that, the manipulation possible on only one side makes it even more difficult.

And so I started to think whether there was a way to manipulate Multicast so that we could just route the multicast traffic over the backup link.

But then think about something known as RPF. As multicast flows it will perform a reverse path forwarding for the packet at every hop. So till your OSPF routes don’t be pointing in the opposite direction, its not going to work.

I also though about creating static mroutes for the particular multicast traffic, but once applied, we could not failover to the primary path if the backup went down. Creating static mroutes with tracking is not an option.

So I am back to the square one. But am still working with the scenario. I have a couple of guys on my team work on it. Seems that we are closer to a particular solution, but it doesn’t seem best practise.

Will let you know tomorrow for any updates.

Regards

Rustom Billimoria

CCIE R/S#24798

New Member

Re: manipulate ospf routing

Hi Rustom,

Thanks a lot for your efforts so far taken to fullfill my requirement.  really appreciated .no words.

If i dont find a best solution for my current requirement i may think about working out the below scenarios

1) Upgrade the STM-4 to STM 16

2) Request( somehow convince them) other end to static route to my new subnet 10.20.6.0/24  towards BACKUP STM-4 from their end both routers. I think this way i can get it done..hope there wont be any issue on the Multicast flow .

Kindly look in to 2nd option and let me know it is a workable solution.

Thanks again for efforts.

New Member

Re: manipulate ospf routing

Hi Rustom,

Hope you are doing well.

Can u respond to my last query if possible. Thanks

New Member

Re: manipulate ospf routing

Hi Rustom,

Any update on this. thanks

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