If you are hoping that 40% of the traffic will go over one interface, and
60% will go over the faster interface, OSPF can not do that (EIGRP/IGRP can
with the variance command for unequal loading).
However, OSPF will automatically load balance over up to 4 equal cost paths.
You can set the OSPF cost for each interface to be the same using the ip
ospf cost command.
Some info from Cisco about your question:
HTH,
Charles
>From Cisco TAC Q&A Forum
Q: How does OSPF calculate its metric or cost?
A: OSPF uses a reference bandwidth of 100 Mbps for cost calculation. The
formula to calculate the cost is reference bandwidth divided by interface
bandwidth. For example, in the case of Ethernet, it's 100 Mbps/10 Mbps = 10.
Note: If ip ospf cost <cost> is used on the interface, it overrides this
formulated cost.
Question: Does OSPF automatically load balance or are additional commands
needed? (I have parallel T1 serial links going between an OSPF Area 0 router
and an Area 1 router.)
Answer:
The router will load-balance over two T1 links if it sees equal OSPF costs
to a given destination. The default is up to four parallel paths, and in
your case, it should be two. You can verify this by doing a sh ip route and
look for two paths to a given destination network across the WAN links.
Also, if IP fast-switching is turned on, the router will load-balance on a
per-destination basis, and if IP fast-switching is turned off, the router
will load-balance on a packet-by-packet basis.
...and also...
Question: Does OSPF support load balancing among serial lines?
Answer:
Yes, load balancing works in OSPF with up to four equal-cost paths, serial
or otherwise.
Internetwork topologies are typically designed to provide redundant routes
in order to prevent a partitioned network. Redundancy is also useful to
provide
additional bandwidth for high traffic areas. If equal-cost paths between
nodes exist, Cisco routers automatically load-balance in an OSPF environment
.
Cisco routers can use up to four equal-cost paths for a given destination.
Packets might be distributed either on a per-destination (when fast
switching)
or a per-packet basis. Per-destination load balancing is the default
behavior. Per-packet load balancing can be enabled by turning off fast
switching using
the no ip route-cache interface configuration command. For line speeds of 56
kbps and faster, it is recommended that you enable fast switching.
"HYniuniu" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]...
> We paln to have two leased lines connected between two routers. One
> line is 512K and another is 768K. Can we load balance between these two
> lines by using ospf? If can, how to? Eager for your advice. Thank you
> very much!
>
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