The MPLS WG Archive

["Manral, Vishwas" <VishwasM@netplane.com>]

Hi Jeff,

I guess in Section 4.0 of draft
http://www.ietf.org/internet-drafts/draft-ietf-isis-traffic-04.txt it is
stated that

   If a link is advertised with the maximum link metric (2^24 - 1), this
   link should not be considered during the normal SPF computation.

So if we want to preclude a link from normal SPF and yet use it for MPLS
LSP's we can set the metric to the value 2^24 - 1.

Thanks,
Vishwas

-----Original Message-----
From: Jeff Parker [mailto:jparker@axiowave.com]
Sent: Friday, June 28, 2002 10:57 PM
To: 'mpls@UU.NET'
Cc: 'ccamp@ops.ietf.org'
Subject: Control vs Client Links in IS-IS TE


Consider a service provider who wishes to distinguish his control traffic
from the network he provides subscribers, by distinguishing his control
links, running pure IP traffic and the IS-IS protocol, from MPLS LSPs that
only run customer traffic. 

Imagine an MPLS router A that has some IP control interfaces and an MPLS LSP
to router B.  How can IS-IS distinguish the two types of links if it is
using wide metrics?

In OSPF, we can send an Opaque LSA with info about an LSP.  This will not be
used for the IGP's SPF.  
However, TLV 22 in ISIS always includes 3 bytes of default metric, and thus
looks like a normal link from A to B when the router is using Wide Metrics
in the SPF.  If B also has an LSP to A, other routers will have no way to
distinguish an MPLS LSP link intended for CSPF and those to be used in the
IGP's SPF.  I could imagine using a field such as Switch Capability, to
decide if a link should be included in SPF or not, but haven't seen this
suggested anywhere.  

- jeff parker
- axiowave networks