The MPLS WG Archive

["Dave Humphrey" <dave.humphrey@telindusk.net>]

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As I understand it with nocspf specified the path is worked
out on a hop by hop basis at each transit router. With cspf
enabled a fully computed ERO is handed to RSVP in order for it'
to signal an exact path and no other.

Dave Humphrey

- -----Original Message-----
From: Mareline Sheldon [mailto:marelines@yahoo.com]
Sent: 07 September 2001 15:33
To: Dave Humphrey; giles@packetexchange.net
Cc: mpls@UU.NET
Subject: Re: several questions


Pl. refer to the white paper by Chuck Semeria "RSVP Signaling
Extensions
for
MPLS Traffic Engineering" by Juniper Networks.
There in Pg. 11 it says very clearly under the section "Establishing
an
LSP
Tunnel" that "In addition to the LABEL_REQUEST object, an RSVP path
message
can also contain a number of *optional* objects:" and there it
mentions
as
the first item "ERO-Can be added to specify the predetermined .. "

Pl. clarify

Regards,
Mary

- ----- Original Message -----
From: "Dave Humphrey" <dave.humphrey@telindusk.net>
To: <giles@packetexchange.net>; "Mareline Sheldon"
<marelines@yahoo.com>
Cc: <mpls@UU.NET>
Sent: Friday, September 07, 2001 7:21 PM
Subject: RE: several questions


>
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> Juniper computes the ERO from the Traffic engineering database
> the path signalled follows exactly that created by the ERO. If
> it can't create it the LSP won't get set-up. JUNOS thus does
> use the ERO.
>
> Dave Humphrey
>
> - -----Original Message-----
> From: Giles Heron [mailto:giles@packetexchange.net]
> Sent: 07 September 2001 13:46
> To: Mareline Sheldon
> Cc: mpls@UU.NET
> Subject: Re: several questions
>
>
> Mareline Sheldon wrote:
> >
> > Please find my comments inline ..
> >
> > ----- Original Message -----
> > From: "Giles Heron" <giles@packetexchange.net>
> >
> > > > topology into areas and so on.
> > >
> > > But the opaque LSAs used for TE don't cross area boundaries. 
> > > So 
> whilst
> > > you can divide the network topology into areas you can't
> > > actually do
> TE
> > > across those areas.  But there is ongoing work on multi-area TE
> > > to
> fix
> > > this...
> >
> > Don't we use opaque LSAs of link-state-type 11 in TE which are
> > flooded throughout the AS ?
>
> TE is carried in type 10 LSAs.  So only flooded through the area.
>
> > > > Explained above. You can use route summaries .. and hence
> > > > proves
> that
> > MPLS
> > > > is scalable ;-)
> > >
> > > Well, sort of.  Like I say, CSPF won't work across area
> > > boundaries.
> > >
> > > And if you are using LDP (not CR-LDP, that doesn't seem to
> > > exist in
> any
> > > approximation of reality) to signal your LSPs then route
> > > summaries
> are a
> > > bad idea, since you need the FECs to match prefixes in your
> > > IGP. 
> >
> > I am not really sure if CR-LDP doesn't seem to exist any more ..
> Nokia,
> > Nortel Networks and a lot of other giants are still actively
> > involved
> in the
> > development of CR-LDP. But then i may be wrong !
>
> When was the last time you saw a router built by Nokia or Nortel?
>
> They are hardly "giants" in the TCP/IP world.
>
> For better or worse CR-LDP is dead (at least wrt MPLS.)  Can't
> speak for
> GMPLS.
>
> > > > Please note that EXPLICIT_ROUTE object (ERO) is an optional
> > > > objetc
> > contained
> > > > in an RSVP PATH message. It is *only* when the ERO is
> > > > present, the
> RSVP
> > PATH
> > > > message is forwarded towards the egress LSR along the path
> specified by
> > the
> > > > ERO, *independent* of the IGP shortest path.
> > > >
> > > > Thus by default the path taken is the one guided by the IGP
> running !
> > >
> > > But YMMV depending on the RSVP-TE implementation in your
> > > router. 
> Some
> > > boxes always send an ERO I think?
> >
> > I am not so sure if the boxes always send an ERO .. and i dont
> > think
> Juniper
> > does that .. atleast they dont claim to do so !
> > btw whats YMMV ??
>
> Your Mileage May Vary.
>
> - From what I remember a certain other big router vendor always
> sends an
> ERO.  But since I don't have one in front of me to test on I can't
> be definitive right now :)
>
> > > > traffic is transferred to it before the old LSP tunnel is
> > > > torn 
> down.
> > >
> > > I'm not sure that you have answered the question here?
> >
> > Hmmm .. if there are no resources available at a *particular* LSR
> > then
> why
> > can rerouting be done ??
> > I'm confused ..
>
> But his question wasn't about re-routing?
>
> It was about an LSP setup which hits a problem at an LSR which has
> insufficient resources to complete the request.   In that case the
> LSP
> setup fails, and the head-end LSR has to re-signal.
>
> Giles
>
> - --
> =================================================================
> Giles Heron    Principal Network Architect    PacketExchange Ltd.
> ph: +44 7880 506185              "if you build it they will yawn"
> =================================================================
>
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