DR Site - Help with OSPF

opers13

Guys,

I need to put together a proposal for DR. We are currently routing between sites 1, 2, 3, 4 with EIGRP, but I want to change to OSPF and add the DR site and Site 5 to OSPF.

At main Site 1, I want to do equal cost paths to the internet and split some of the load.

I'm just not 100% sure on how to config OSPF between all sites and have them redundant.

thanks for your help!

Turgon

Your requirements are a bit loose leaving any designer many alternatives. You might consider an area 0 encorporating the EIGRP AS I imagine you presently use for 1,2,3,4. Site 5 perhaps a stub area. The DR site in a non-zero area.

Try and lab this up and practice permatations. Run ip debug routing when you unplug an interface so you can see how the resilience works when a link fails. So far as load sharing out your two internet pipes, how about a couple of default routes on site 1? Or you could look at being multihomed. using BGP. If it's the same ISP providing both pipes contact them for advice as you will not be the first customer needing confirmation on this sort of thing. They should be able to advise you on appropriate configurations.

Certainly lab this up. You need to be sure your OSPF solution is water tight. Then your next issue is planning the migration. Before you get into any cute ideas like redistribution just remember that your EIGRP internal routes are preferred over OSPF. Keep your design as simple as possible!

Just a thought, but if any consultant was called in to design this for you the project could run for months while the analysis is conducted and solutions tested on a reference model before a migration is planned, much less implemented. And these guys cost a lot of money.

Therefore, ensure your boss gives you plenty of time to do your own research. If your rush this sort of work with the costs involved it will be a disaster.

Good luck!

CCIE-4-HIRE

Why are you using eigrp in the first place? Are you using other protocols that might require eigrp? Why do you want to introduce ospf if you are now using eigrp? Redistribution is generally not recommended as a long term solution. Do you have a reason or defense for your design and goals? I'm sure you do but just in case.

At the main site, why do you want to do equal load balancing between a 5mb and a 1 mb pipe to the internet? Consider each route to the main site internet and what will happen if any of the sites go down. Now be very careful here and try everything if you can. Use debugging or a sniffer and log the results as closely as you can. You have a lot of points of failure. You should fail each one and ensure you understand what exactly is going to happen in any event. This may be helpful as a baseline later if or when something does fail.

Are you going to monitor the links on each site's routers? I ask because it may be helpful if something does fail to have one or more location perform both monitoring and logging so that you can triangulate where the failure occurred. It may reduce your time diagnosing and returning the failed link to full service. In some cases you may have a failure and never know it otherwise.

I am no expert but these are things that come to my mind.

opers13

Sites 4 and 5 are not important. We would route OSPF only, EIGRP would be gone. Doing equal load balance to the internet was just an idea in case we replace the T1 with a bigger pipe.

Should I make all sites a single area or split into 2 or more areas?

dtlokee

For your connection to the Internet you have 3 different egress points, are they all to the same provider or different ones? You don't really want to use 2 static routes to the provider as this will lead to the router sending traffic equally across both links and you will end up with drops and jitter because of the slower speed T-1. You may want to use policy routing to put some of the less desirable traffic across the T-1 or somthing to that effect.

Check the router CPU and memory stats, if there is enough power left there you can implement OSPF and leave EIGRP in place, check all you topology tables and make sure things are going as you want, then strip EIGRP out and the OSPF routes will fall in (higher AD). Keep in mind when you design your OSPF areas the routers will prefer an Intra-area route over an ineer-area route, so if you were to make sites 2 + 3 on site they would prefer the route over you backup route, if that is not what you are looking to do then make them seperate areas.

Turgon

opers13 wrote:

Sites 4 and 5 are not important. We would route OSPF only, EIGRP would be gone. Doing equal load balance to the internet was just an idea in case we replace the T1 with a bigger pipe.

Should I make all sites a single area or split into 2 or more areas?

Yes I didn't notice the different internet pipe speeds at first. I imagine it would work ok until the T1 limit is hit but would then start to have problems so it's not a solution. You might potentially be able to do something called traffic share balanced with EIGRP to utilise the unequal links, but you want to move away from EIGRP and you would need help from your ISP. Redistributing a default route into EIGRP to achieve this may be unworkable.

Look at static routes or BGP and CEF to spread the load once your pipes are more in line with one another speed wise.

For OSPF, try one big area 0 for now (it's not that big) and lab it up. Pay attention to the potential problem dtlokee has brought up - the use of the backup link between area 2 and 3 and look for other problems. You may be able to get around these by playing with cost metrics or by having to use more areas. Whatever configuration you use will work in a certain way, but you must determine if that operation violates your companies preferred routing policy.

Paul Boz

I'm assuming that all of your traffic is going through your central office and out the internet, right?

If that's the case, just configure each remote site in its own stub area and set a default route to area 0 (the central office).