From: Robert Rech (rjrech@xxxxxxxxxxxx)
Date: Tue Jul 09 2002 - 15:14:34 GMT-3
OSPF does load balance on equal cost paths, it uses (100mb)
100000000/link speed to determine link cost by default. So if I have 2
paths to a destination as long as the costs are equal. Example 2 routers
with 2 T1's between them left at default and both interfaces in OSPF
would show 2 equal cost routes, apply a bandwidth 64000 statement to 1
of the interfaces and the OSPF cost of that interface will be higher
then the other serial interface {default bandwidth 1544000}. And only 1
route will show up in the routing table. Both will still be in the OSPF
database.
The load balancing depends to some extent on the IOS version and were
CEF is being used. Normal equal cost paths will use a per-destination
load sharing. For example if there are 2 paths the 1st destination will
use the 1st path and the 2nd destination will use the second path and so
on. Now if most traffic is destined to a single destination address
{such as a PAT address} this might not help. This is were CEF comes in
and will alternate paths on a per-session {source-destination} basis.
EIGRP uses a more complex formula including load.
RIP II will uses multiple paths.
BGP will also but not by default.
Robert Rech
Senior Network Engineer
Cap Gemini Ernst & Young
Kansas City Service Center
rjrech@cgeykcsc.com
phone (816) 459-4767
fax (816) 459-6767
>>> elping <elpingu@acedsl.com> 07/09/02 09:54AM >>>
yes.....up to 4 paths ...if my memory seves me right
"Diehm, Brian" wrote:
> If memory serves me right OSPF does not load balance. Is that
correct?
>
> Brian
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