[c-nsp] Difference in IP FRR Link vs Per Prefix Option

[Phil Bedard]

Here is a good document with regards to Cisco's implementation:

http://www.cisco.com/web/SK/expo2011/pdfs/IP_Fast_reroute_PeterPsenk.pdf


Per the way LFAs are calculated in the RFC per-link doesn't guarantee node
protection but depending on the topology it can provide it.  However a
vendor may choose to calculate the per-link backup path to be a
node-protecting one if they choose and the topology allows it.  Per-prefix
may result in different backup paths based on your topology for two
prefixes which take the same next-hop during normal conditions.  By
default Cisco will try to make a per-prefix LFA bypass the next-hop node
resulting in node protection.

Juniper uses a more efficient implementation and only does per-prefix, but
you can pick and choose whether or not you want link or node-link
protection.  Node-link just adds another step in making sure the path.
Not sure abou the ALU implementation.

Phil 


On 6/4/13 2:43 AM, "Dhamija Amit" <amiitdhamija at yahoo.com> wrote:

>
> Hi 
>
>Can some one help me in understanding the exact difference in IP FRR Per
>Link and Per Prefix option , It's mention in some docs that coverage of
>protected prefixes will be more in per prefix option , If we have per
>link then all the prefixes learned through same link will be covered in
>LFA computation then what else is left for any router the IGP prefixes
>will be learned through some link and if link is protected means all
>prefixes are protected then how can we say coverage is more in per prefix.
>
>I see some vendors Juniper , ALU doesn't supports per prefix option.Could
>you please elaborate more on this.
>
>Thanks for help
>
>Regards
>Amit Dhamija
>
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