[j-nsp] OSPF LFA and LDP LSPs

[Alex]

Serge,
Do you have "track-igp-metric" configured under LDP? I am pretty sure it 
does not since your OSPF and LDP metrics are different but I'd like to 
confirm.
Please try to configure "track-igp-metric" for LDP and re-run MPLS 
traceroute.
Rgds
Alex


----- Original Message ----- 
From: "Serge Vautour" <sergevautour at yahoo.ca>
To: "Clarke Morledge" <chmorl at wm.edu>; <juniper-nsp at puck.nether.net>
Sent: Tuesday, March 16, 2010 2:54 PM
Subject: Re: [j-nsp] OSPF LFA and LDP LSPs


> Hello,
>
> Thanks for your comments. I agree with your theory. It's my understanding 
> as well. What I don't get is why the "traceroute mpls ldp" command uses 
> both paths and yet "traceroute ip" uses 1 path. It's like the backup path 
> is being used by the LDP LSP when it shouldn't be...
>
> Serge
>
>
>
> ----- Original Message ----
> From: Clarke Morledge <chmorl at wm.edu>
> To: juniper-nsp at puck.nether.net
> Cc: Serge Vautour <sergevautour at yahoo.ca>
> Sent: Tue, March 16, 2010 11:35:30 AM
> Subject: RE: [j-nsp] OSPF LFA and LDP LSPs
>
> Serge,
>
> Part of what you wrote included this:
>
>> Now I turn on OSPF LFA "link-protection" on the links and re-run the same 
>> tests:
>>
>> -----------------------
>> se36152 at PE1-STJHLab-re0> show route 10.10.80.2 logical-system PE10 detail
>>
>> inet.0: 34 destinations, 34 routes (34 active, 0 holddown, 0 hidden)
>> 10.10.80.2/32 (1 entry, 1 announced)
>>        *OSPF   Preference: 10
>>                Next hop type: Router
>>                Next-hop reference count: 26
>>                Next hop: 10.10.81.10 via xe-0/3/0.0 weight 0x1, selected
>>                Next hop: 10.10.81.23 via ge-1/3/3.0 weight 0xf000 
>> <--------- Huh???
>>                State: <Active Int>
>>                Local AS:   855
>>                Age: 4  Metric: 2
>>                Area: 0.0.0.0
>>                Task: OSPF
>>                Announcement bits (3): 2-LDP 3-KRT 5-Resolve tree 2
>>                AS path: I
>>
>> inet.3: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
>>
>> 10.10.80.2/32 (1 entry, 1 announced)
>>        State: <FlashAll>
>>        *LDP    Preference: 9
>>                Next hop type: Router
>>                Next-hop reference count: 3
>>                Next hop: 10.10.81.10 via xe-0/3/0.0 weight 0x1, selected
>>                Label operation: Push 299776
>>                Next hop: 10.10.81.23 via ge-1/3/3.0 weight 0xf000 
>> <--------- Huh???
>>                Label operation: Push 299856
>>                State: <Active Int>
>>                Local AS:   855
>>                Age: 4  Metric: 1
>>                Task: LDP
>>                Announcement bits (2): 2-Resolve tree 1 3-Resolve tree 2
>>                AS path: I
>
> I can not speak to your traceroute issue, but my understanding is that the 
> next-hop 10.10.81.23 references are the alternate paths that get put in 
> your routing table by the LFA algorithm.  These routes exist but only in 
> "stand-by" mode.  So if the 10.10.81.10 next-hop ever goes away, traffic 
> can immediately use this "stand-by" routing entry to forward the traffic 
> while OSPF is recalculating new routes under the covers.  This is loosely 
> analogous to how Detours work in RSVP/MPLS Fast ReRoute -- though, 
> admittedly, Fast ReRoute is much more involved.  Then, once the OSPF 
> recalculations are done in LFA, the routing table is updated with a new 
> primary routing entry and another "stand-by" entry.
>
> Therefore, LFA effectively doubles the size of your routing table to 
> accommodate all of the "stand-by" routes.
>
> Unless, I'm missing something, that is at least my understanding of how 
> LFA actually works --- or at least how it is supposed to work.  In other 
> words, per your routing table it is working as designed.  However, this 
> does not necessarily mean that OSPF LFA currently solves all of the 
> problems with microloops in some topologies.  If someone has a better 
> explanation, I'd like to know, too.
>
> Clarke Morledge
> College of William and Mary
> Information Technology - Network Engineering
> Jones Hall (Room 18)
> Williamsburg VA 23187
>
>
>
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