[j-nsp] not defining no-cspf

[magno]

Hello Amid.

1) CSPF is a modified flavour of the normal spf algorithm which is the core
of the ospf & isis protocol. If you set up an lsp with RSVP, and you are
using TE extension with isis (on by default) and OSPF (you must turn on the
use of opaque LSA type 10 (area scope) with the knob "traffic-engineering",
these IGPs will populate the "TED" (Traffic Engineering Database) and when
the RSVP will use the IGP to setup your LSP (without ERO for instance), the
RSVP will take a look at the TED and a modified SPF will run.
All the links which won't satisfied some requirements will be taken out of
the calculation. At the end of the calculation, the CSPF process will give
to RSVP an ERO list (not setup manually by you, but calculated by CSPF
itself) and this ERO list will be used to setup the LSP. If you want to use
link administrative groups (link coloring) or FastReroute you will have to
use the CSPF.
Specifically, the CSPF Algorithm states that:
 1) Prune links with insufficient bandwidth;
 2) Prune links that don't include the administrative-groups
 3) Prune links that contain excluded administrative-groups
 4) Calculate shortest path from ingress to egress consistent with manually
configured ERO
 5) If equal cost paths exist, choose the one whose last hop is the LSP end
point
 6) Select among equal-cost paths (least hop then fill related criteria
(most fill, least fill)
 7) Pass EROs to RSVP

2) OSPF traffic-engineering is the knob you need to enable
traffic-engineering using OSPF (with ISIS it's up by default).So, you'll
find in the ospf database a new 'section' populated by LSA type 10, and
these LSAs will contain link information such as bandwidth constranint, link
administrative group, TE metrics, (for each setup priority 0-7). These
information will be used to populate the TED.

Hope this helps

Massimo

On 5/20/07, Amos Rosenboim <amos at oasis-tech.net> wrote:
>
> Hello Hamid,
>
> As far as I  know if you configure no-cspf then the router will not
> run cspf to set up the LSP. This means that no administrative factors
> will be taken into account and the LSP will follow the IGP path.
> I used it (thanks to a tip from this list) to establish rsvp lsp
> across ospf areas.
>
> I'm not a big expert on this, so you might want to hear a second
> opinion.
>
> As for ospf traffic engineering, it is meant to enable ospf to carry
> the additional  information required for TE (mainly link bandwidth).
>
> Regards
>
> Amos
>
> On May 19, 2007, at 6:38 PM, Hamid Ahmed wrote:
>
> > Hi all,
> >   Can anyone explain me the following  please :
> >
> >   1) what are consequences of if i donot define no-cspf command
> > while i configure a explicit LSP configuration with ERO consttraints ?
> >   2) what is the purpose of ospf traffic engineering ?
> >
> >   Best regards,
> >   HA
> >
> >
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