OSPF does equal cost load balancing and if you have two routes with equal cost to the destination then OSPF will load share.

Mr muammad asghar khan thank you so much for reply. however, I am wondering if this cost is just based on the bandwidth, the router will may send more packet on the interface with high bandwidth and other interface will not be consider. this acting can cause congestion. is there any metric in cost formula that considers packet sending rate too?

Yes,you are very much right,however there is an option to control the flow of packets across the network, OSPF allows you to manually assign a cost (or metric) to a particular path segment.

The following link might be helpful for you.

http://www.sciencedirect.com/science/article/pii/S0305048306000569

thank you so much for the link. however, I would like to know the recommendation of Cisco regarding this problem. I mean I would like to know the solution that Cisco is considered.

thanks

If you want traffic engineering capabilities you have to use MPLS-TE in conjunction with OSPF.

Other than that OSPF only supports equal cost load balancing.

There are too many unspecified parameters to answer your question accurately. Suffice to say that each of interface running OSPFs even if they are different interfaces, i.e. Fast Ethernet vs Gigabit Ethernet, will still have a default cost metric of 1 (this is the primary factor).  In other words, OSPF equally routes packets across the different interfaces; traffic is not routed over the fastest interface just because it is faster.

This behaviour occurs because the default reference bandwith for OSPF in IOS is 100Mbit/s.

The formula that is used to calculate the costs of a link is:

"reference bandwidth"/"interface bandwidth"

Using the default reference bandwidth Fast Ethernet and Gigabit Ethernet both have the same costs of 1 and equal cost load balancing occurs.

If you change the default reference bandwidth to a higher value or if you use interfaces that are slower than 100Mbit/s no automatic equal cost load balancing occurs.

But as John said more infos are needed to answer your question accurately.

thank you so much dear Ulrich and John. I have studied  MPLS-TE.  However, I have been searching formula contains different metrics used by Cisco router  that consider load balancing. First , I thought OSPF policy can satisfy my condition. However, after searching more I came to  know that EIGRP is more suitable since it uses different metrics as follows :  

"EIGRP uses these scaled values to determine the total metric to the network:

metric = ([K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)]) * 256 " ( http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html#anc37 )

However, I will become so happy if I hear any other suggestion or comment.

again thank you so much for your helps and your time

regards

If you end goal is to manage network congestion, then I suggest you start by reading QoS: Congestion Management Configuration Guide by CISCO (http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conmgt/configuration/xe-3s/qos-conmgt-xe-3s-book.pdf). I am not sure you will be able to resolve network congestion just by tweaking any one of the network protocols – these protocols are not holistic: they only address specific network routing aspects within Intra-AS Routing [routing within the same Autonomous Systems (routers within an AS use an Interior Gateway Protocol (IGP) such as RIP, OSPF, IS-IS, EIGRP)] and Inter-AS Routing (between different networks). That is why Cisco came up with Weighted Fair Queueing (WFQ). Such a congestion management feature (and its subsets) que packets at an interface until the interface is free to send them. According to their assigned priority and the interface’s configured queueing mechanism, they are then scheduled for transmission. The router controls which packets are qued (and serviced with respect to each other) to determine the order of packet transmission. Note that there are always restrictions: tunneling and encryption cannot use WFQ -- they change the packet content information required by WFQ for classification.

Thanks John for all explanations and suggestions . I will study the congestion management document. however, you mentioned a nice point ; " tunneling and encryption cannot use WFQ"

thanks

regards