07-04-2016 02:20 AM - edited 03-05-2019 04:21 AM
Hi Guys,
I am working on something and need a fairly quick answer and cannot run a lab and test.
How does OSPF convergence work when on link fails? it doens't store any backup path like eigrp does it ?
it will recalculate the path.
Is there a way to have a redandunt route in place to quickly failover ?
if not does anyone know how long the convergence take using SPF algorithm ? is my question like how long is a peice of string ?
Thanks
07-04-2016 06:31 AM
If you configure LFA feature, OSPF will be immediate to switch-over to the backup route.
07-05-2016 12:43 AM
many thannks, does bgp support a multiple backup route like eigrp ?
07-05-2016 04:25 AM
BGP is more flexible than OSPF it can have multiple paths installed in the BGP table waiting to take over from the primary , depending on your design and what your trying to do there are a few ways to achieve it , one way below is install command
bgp additional-paths install
http://www.cisco.com/c/en/us/td/docs/ios/iproute_bgp/command/reference/irg_book/irg_bgp1.html#wp1117217
With BGP though its best not to have a redundant path as it will be wan and costly to have sitting there so usually you would load share the links so there all used at once and at the same time use bgp path attributes so there backed up between each wan link
07-05-2016 05:35 AM
many thanks, so what you are saying is there will be no convergence ?
if you use ospf and tune the metric to load balance across three links, if one dies, does it trigger spf algorithm ? would you loose connectivity ?
07-05-2016 06:39 AM
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How does OSPF convergence work when on link fails?
Normally, it recomputes a new best path.
it doens't store any backup path like eigrp does it ?
Normally, no.
Is there a way to have a redandunt route in place to quickly failover ?
Normally, no, but if you have two equal cost paths, besides using both normally, it will just use the remaining one.
if not does anyone know how long the convergence take using SPF algorithm ? is my question like how long is a peice of string ?
Laugh, yes much like how long is a piece of string.
Many variables are involved. Convergence time is impacted by design and configuration settings. The latter, when properly set, can lead to pretty quick OSPF convergence with a link failure. See http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/routed-ex.html#wp998679
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