Equal Cost Load Balancing on OSPF OR Equal Cost Load Sharing on OSPF or Equal Cost Multipath Load Balancing on OSPF

[r20039r20039]

Hi Friends

Which term is correct ?

Equal Cost Load Balancing on OSPF  OR

Equal Cost Load Sharing on OSPF or

Equal Cost Multipath Load Balancing on OSPF 

I want to achieve Equal Cost Load Balancing (What is this actually?) over OSPF which will also support Failover  between R2 and R3. 

I am confused about Equal Cost Multipath (ECMP) and ECBL (Equal Cost Load Balancing) . 

Do they both support Failover? 

I have tested 

                                                           OSPF

    PC1-----------Router 1 ----------------------------------------Router2-------------PC2

                                     -----------------------------------------

In the above scene, If I have tested that any file sent from PC1 to PC to uses both the parallel Links at the same time and severing any of the links still sees the attached link sending data to PC2 . What is this called?

 What if I have a topology like the following? Would that be called as ECBL or ECMP ? Very confused. 

[e.ciollaro]

As fas as I know ECMP means that there are two paths both having the same administrative distance and cost. ECLB means that traffic is load balanced across the different equal cost path. Note that generally speaking:

• ECLB doesn't imply that router balances traffic between the two paths, for example in EIGRP  you can configure traffic-share min and both paths are in routing table but traffic isn't balanced or configuring OSPF and other routing protocols using maximum-path 1
• in EGRIP load balancing could be over unequal paths

Finally both ECMP and ECLB use the second link in case of failure of the first one.

[r20039r20039]

So what youre referring is 

ECLB and ECMP does almost the same thing other than one has same admin distance and cost and the other has different admin distance and cost 

is that right?

[Richard Burts]

I have trouble relating the drawing that you post with the question that you ask. The drawing shows a source and three routers. But I do not see anything in the drawing that would indicate any equal cost paths from the source to anywhere. Can you clarify this?

In the way that the terms are frequently used they are pretty much interchangeable and mean pretty much the same thing. If you look at the terms for their technical detail they are not really the same and only one of them is technically correct when discussing packet forwarding in IOS routers. When there are multiple equal cost paths to a destination IOS will "share" the traffic on the links with some packets using the first link and some packets using the second link. When we talk about balancing the traffic there is am implication that the amount of traffic on each link is equal. And that is not guaranteed when using multiple equal cost paths with OSPF (or with EIGRP). Here is a very simple demonstration of what I mean: think about a network with two equal cost paths to reach 10.11.12.13. So we send 3 packets over link 1 and 3 packets over link 2, which sounds like balancing. But what if the 3 packets on link 1 are 100 bytes each while the 3 packets on link 2 are 1500 bytes each? Link 1 has transmitted 300 bytes while link 2 has transmitted 4500 bytes. Would you call that balancing or sharing?

HTH

Rick