Subject: RE: Static LSP Configuration

From: Shahram Davari <[email-masked]>
Date: Mon, 6 May 2002 06:31:41 -0700

Hi,

If one wants to have only 2 LSPs (one working and one backup) in his network, why should
he run LDP?

-Shahram

> -----Original Message-----
> From: Sukanta ganguly [mailto:[email-masked]]
> Sent: Sunday, May 05, 2002 1:43 PM
> To: Ron Bonica; Brijesh Kumar; 'Curtis Villamizar '; 'Ajay Simha '
> Cc: [email-masked]; 'gary tam '; [email-masked]
> Subject: RE: Static LSP Configuration
> 
> 
> In a fairly controlled and static environment it may
> work, but in other situations it will create
> unresolved links and packet drops, with no recovery to
> the failure.
> 
> SG
> 
> --- Ron Bonica <[email-masked]> wrote:
> > >
> > > Also, on your:
> > > >>btw- retorical question - with static LSPs, what
> > happens when a link
> > > goes down?
> > >
> > > Should the expected behaviour  need to be any
> > different than when someone
> > > routes with static routes?
> > >
> > > Cheers,
> > >
> > > --brijesh
> > >
> > >
> > 
> > Brijesh,
> > 
> > Statically configured LSPs blackhole traffic when a
> > link in the middle of
> > the LSP fails.
> > 
> > The LSR immediately upstream of the failure discards
> > all traffic belonging
> > to the LSP. This is because that LSR may not look
> > beyond the MPLS label to
> > forward the traffic. See RFC 3031 Sections 3.18 and
> > 3.22 for details.
> > 
> >                                                   
> > Ron
> > 
> 
> 
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---

From: Curtis Villamizar <[email-masked]>
Date: Wed, 08 May 2002 12:12:01 -0400

In message <[email-masked]
>, Shahram Davari writes:

The obvious answer is so when the next Amtrak train hits fiber on both
sides of the track, [for brevity omit dozens of other examples of
multiple failures, some massive, that have occurred in the last 5-10
years], there is still a connection.  But this may be to "core"
centric.

Static IP routes are fine for something that has only one path to "the
rest of the world".  That is unacceptable to an IP provider but OK for
customer circuits in cases where cost outweighs possibility of lengthy
outage.  In this circumstance, configuration is simple.  From the
provider, customer network it "that way"; from the customer the rest
of the world (IP default route) is "the other way".

Unlike static IP, static LSP does not offer the simplification of
configuration.  If there is a singly connected "last mile" over which
a subset of IP traffic is a tunnelled L2 circuit, then it makes sense
to advertise LDP and BGP (filtered, just like IP routes to the
customer are filtered), and allow the BGP-VPN to establish the E2E LSP
needed for the VPN.  If the BGP-VPN is moved to the other side of that
last mile, then the access router (provider side of customer circuit)
has a bit more work to do and the CPE has a static.  This is no less
work for the provider and is one more thing that can become
inconsistent do to slight misconfiguration and fail.

Even if the provider were to take this approach, the provider edge
would have LDP (optionally over TE) on the core side.  In one case
there would be filters programmed on the provider edge and limited LDP
and BGP exchange.  In the other case, a fixed label and interface
would be directed into a LDP tunnel.  At the other end the mapping
would have to be reversed.  In the dynamic case, there is
configuration only at the ingress (CPE) for each direction.  In the
static case, for each direction four routers must have static
configurations that match and the provider edge router must have a
label mapping for each customer VPN and each customer prefix rather
than just for each customer prefix.  Unlike static IP this does not
simplify configuration and reduce load on the provider edge router, it
may make matters worse.

Regardless, maybe some provider prefers this approach.  Some providers
consider no exchange of routing information with the CPE to be a goal.
I have yet to hear a provider ask for this but we don't come that
close to the provider edge (gateway and aggregation is about as close
as we get to the edge at this point) so it may be that there are
service providers wanting to do something like this.

Can we please now take further discussion off list.

Curtis