route selection in OSPF

09.23.08   |  
‎09-23-2008 06:19 AM
Hi all, I got an issue with route selection in OSPF. If I have 5 intra-area routes all of equal cost, what that JUNOS does...I have ECMP enabled through a policy under routing-options..I expect it to do a load-balancing per-flow..Am I right?


Re: route selection in OSPF

09.23.08   |  
‎09-23-2008 06:42 AM

In Junos the OSPF load balancing is per destination by default.


You can change it to per flow by using the following configuration (NOTE: per-packet == per-flow)


routing-options {      

forwarding-table {          
export load-balancing-policy;      }  }  

policy-options {      

policy-statement load-balancing-policy {          
then {              
load-balance per-packet;          }   }  }
I hope this helps 

Re: route selection in OSPF

10.15.08   |  
‎10-15-2008 07:31 PM

Traffic pattern will vary depending on the ASIC.  Internet Processor I ASIC is truely per packet while II's are per flow.



Re: route selection in OSPF

10.16.08   |  
‎10-16-2008 02:25 AM

Hi Shiv,


It also depends upon the spread of the sources/destinations.  The actual hash algorithms used to decide which of the equal cost paths to use are proprietary and not published.  However, I can say that if you have a very small cluster of sources and a very small cluster of destinations, there is a possibility that the balancing will not be very... well... balanced.  With a reasonable spread of src/dst IP addresses, you'll get a fair (but never perfect) balance.