Unequal bandwidth load balancing with two ISP over ospf

[soumenG]

Hi there !!

Can anyone suggest a solution where I have two locations (H/O and B/O) connected to 2 different ISP with the bw capacity of (1GIG/3GIG) and I want to load balance traffic over two unequal bandwidth links provided by the ISP with OSPF. In the current scenario we are facing issues like when two links are up, our less bandwidth link is getting full and our users are getting hampered. Is there any solution where we can use both of the links and works as with its maximum capacity and then shift the traffic to other links without giving any throughput issue to the less bw link.

Attaching the topology herewith for better understanding..

Thanks in advance.

[MHM Cisco World]

That normal' ospf dont looks to BW anymore when config unequal cost'

Solution is BW of link 1 is twice BW of link2 i.e. 2/1

I have idea of divide the subnet in such we get 2/1 traffic pass through links.

This easy via bgp but for OSPF I need to make lab.

Thanks 

[soumenG]

I don't think capping of bw would help me here I found in some articles. By the way can you share the idea of devide subnet for two unequal bw link 

[MHM Cisco World]

I start bulid lab' some point it need clarify 

1- MLS sw have onle defualt route redistrubte into two areas 11 and 12 

2- where is area0

[soumenG]

We have decided to have a separate ABR so we selected to the BO and which will connect other BO's with the area 11 and 12 for the time being. Not sure if this will scale well or not so need your suggestions. Yes Mls switch is configured to

redistribute default route

MLS is member of area 0 with 2 core switch.

Pl revert,  if I have to re-design the topology I will do that.

[Joseph W. Doherty · Accepted solution]

If your two ISP are in different OSPF areas, you have two (or more) areas in a BO?

If forgoing true, how would you see the same destination across the two areas, to achieve LB?

Are you using actually using ISPs (Internet Service Providers) or SPs (Service Providers), because wondering, how are you running OSPF across the "WAN"?  Or is this some kind of multi-point Ethernet connection?

BTW, understand, when doing most forms of LB, it's static, i.e. one path can be overloaded while another is sitting idle, i.e. even with 3:1 static LB, this would not guarantee users will not get

hammered

on either path.

Sometimes, though, QoS can mitigate users getting

hammered

[MHM Cisco World]

If forgoing true, how would you see the same destination across the two areas, to achieve LB? <<- that what stop me in lab, this impossible happened. 

[Joseph W. Doherty]

Might be done using externals, but I didn't want to presume.

[MHM Cisco World]

I already have two solution 

One branch site config with two router and each router advertise same subnet using different area here we get lsa3 

One router and as you mention redistrubte' but here I add two ospf process one connect to prefix  and then redistrubte into ospf which have two link one link to each area.

Since he accepted solution I will mention my idea which simply use area range and summary.

Area range in one area and advertise full prefix for other area' this give some type of load balance 

For summary same idea.

Anyway he decided to change topolgy.

Thanks 

Have a nice summer 

MHM

[soumenG]

Actually you are right I made a mistake by saying ISP it is the service provider network its kind a point to multipoint architecture. Thanks, I will change the bw capacity to equal and will connect the BO within the same area.

[Joseph W. Doherty]

Yes you could treat as equal, but you might obtain better overall performance using/preferring just the 3g path (as the delta is so large).

Try both and determine which seems to work better for you.

[Joseph W. Doherty]

Possibly the best option would a PIRO varient of PfR.

Or, possibly 3 tunnels on the 3g path vs. 1 tunnel on the gig path and then ECMP the four tunnels.

[Giuseppe Larosa]

Hello @soumenG ,

@Joseph W. Doherty 's suggestion :

>> Or, possibly 3 tunnels on the 3g path vs. 1 tunnel on the gig path and then ECMP the four tunnels.

I would go for this. OSPF should run only on the GRE p2p tunnels and not on the physical links. 3 tunnels would be associated with the link that offers 3 Gbps of bandwidth and one with the other link.

For the best results all these tunnels should be in the same area , either area 0 or non backbone area . I would prefer using area 0 so that at branch office you can use a dedicated area-id and you can have control on what internal routes are propagated to HQ.

Hope to help

Giuseppe

[Joseph W. Doherty]

Ah, in haste I overlooked a key issue, mentioned by @Giuseppe Larosa , i.e., you show the two paths in different OSPF areas.  As OSPF routes intra-area before inter-area, don't believe the multi-tunnel approach would work without getting all tunnels in the same area.

Whether the different areas for PfR/PIRO would be an issue, don't know, but that feature might not be supported on all your WAN devices, especially L3 switches.