02-14-2008 11:23 AM - edited 03-05-2019 09:09 PM
If I bundle 3 gigabit links into a Layer 3 etherchannel, will ospf notice the bandwidth of 3Gbps when it calculates the ospf cost? or does it use 1 Gbp?
02-14-2008 01:15 PM
Hi:
OSPF will definitely treat the EtherChannel as a 3 Gbps link and calculate the Cost accordingly.
Remember that OSPF calculates Cost based on a reference bandwidth of 10 to the 8 (100 million)/configured bandwidth. So, a 100 M FDDi connection defaults to a cost of 1. Anything higher than that will still default to a cost of 1 (since you cannot have a fractional Cost) and nothing will be gained by havin gthat extra bandwidth configured for the interface.
So, to accomodate high-speed links above 100M, use the 'auto-cost reference-bandwidth command while in router configuration mode or use the 'ip ospf-cost' command at the interface to hardcode the Cost.
HTH
VL
02-15-2008 07:03 AM
I set the auto-cost reference bandwidth to 1000000 for future 10Gbps upgrades and the costs dont add up.
What would the formula be for the 3Gbps connection?
1,000,000/3,000 ?
02-15-2008 08:23 AM
Hi;
The formula that Cisco's OSPF implementation uses to determine a link's Cost is 100,000,000 (100M)divided by the reference bandwidth. You have typed 1 million divided by the reference bandwidth.
02-15-2008 08:26 AM
You have way too many zeros for 10Gbps.
The command is reflected in Mbps.
auto-cost reference-bandwidth mbps
for 10Gbps
auto-cost reference-bandwidth 10000
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cr/hirp_r/rte_osph.htm#wp999355
__
Edison.
02-15-2008 09:34 AM
edison:
Good catch. I didnt read his post the way you did. I though tthe final reference bandwidth he configured was 1,000,000 (1M), I didnt think that he may have actually entered "1000000" as the argument in the command itself.
Maybe that's what he did....
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: