Re: RSVP and LDP

Good explanation Hemanth

 TE is used to engineer the traffic as u want to go through with the
prioritized traffic in need of B.W. There many be different LSP's and you
assign different treatment for each LSP.
And also u can do LDP over RSVP where u can do RSVP TE Tunnel from one P to
another P . So from PE to P u run LDP and have a targeted LDP over ur RSVP
So its basically hierarchical LDP over ur RSVP .

On Thu, Feb 2, 2012 at 6:13 PM, HEMANTH RAJ <hemanthrj_at_gmail.com> wrote:

> Hi Mustafa
>
> LDP has been designed for distributing labels exclusively, But RSVP has
> been a Host based protocol to inform the transit routers that to reserve
> the bandwidth what the application needs.
> So here in MPLS TE , RSVP is used as a signalling protocol to establish a
> BANDWIDTH DEFINED LSP from head end router to your Tail End Router
>
> In ur normal LDP , For each prefix u build a particular LSP . These
> prefixes are distributed by ur CORE IGP. SO basically ur LDP is relying on
> ur IGP info for setting up a LSP for that prefix
>
> But in MPLS TE, RSVP will build a LSP with the Tail End Router with some
> constraints. So basically it is a Tunnel where ur Head End Router is trying
> to form with the Tail End and to switch packets on the Tunnel. It is a
> unidirectional Tunnel.
>
> TE also uses ur CORE IGP to check whether the requirements to form a
> tunnel are met. For example , If the TE Tunnel requires 500Kb of bandwidth
> ie ur Head End's routers requirement is 500Kbs of B.W end to end ( Assume
> that there are some users sitting behind Head End Router which requires a
> 500kb feed from the server which is present behind ur Tail End Router ) So
> now ur Head End has to know the end to end B.W capacity of each transit
> router . This information is fed by our CORE IGP which can be ISIS or OSPF
> . ( These r the two protocol in use currently which has the capability to
> carry MPLS TE extended attributes . OSPF uses Opaque LSA and ISIS uses
> extended TLVS for it )
>
> So TE Tunnel will be up only when it is met with these requirements and
> after that it signals the RSVP Path and Tail End will send Reserve Messages
> to assign Labels ..
> This is also same as ur LDP where ur Downstream router starts assigning
> labels to the prefixes.
>
> So basically LDP is a prefix driven label assignment protocol but RSVP is
> all about how ur Head End wants the Constraint driven LSP with ur Tail End
> router and ( so u must know ur network and u know there is greedy hosts
> which wants a feed and u configure the TE Tunnel accordingly )
>
> Without LDP also, RSVP will work .For RSVP u just need ur CORE IGP to be
> converged and has the capabilities to carry TE extended information ( So no
> RIP and EIGRP as of now ) RSVP Head End just sends Path message to ur Tail
> End router to signal each and every transit router that this is the
> requirement
>
> Do not confuse between LDP and RSVP. LDP is always Prefix Driven From IGP
> .. RSVP is basically manually configured Constraint Driven LSP ( knowing ur
> network end to end )
>
> Hope this helps :)
>
>
>
>
>
>
>
>
>
>
> On Thu, Feb 2, 2012 at 5:43 PM, GAURAV MADAN <gauravmadan1177_at_gmail.com
> >wrote:
>
> > I think things are being mixed up here .
> >
> > When RSVP is used with TE .. RSVP will do the label distribution .
> > Hence role of LDP as a protocol for label distibution is eliminated as
> you
> > are doing same thing using RSVP .
> >
> > And also ; i believe that in MPLS L3 VPN scenario as well ; running only
> > RSVP and no LDP anywhere in core can achieve your goal .
> >
> > Regards
> > Gaurav Madan
> > CCIE
> >
> > On Thu, Feb 2, 2012 at 5:14 PM, Mustafa Yadav <mustafa.yadav_at_gmail.com
> > >wrote:
> >
> > > so when ldp is going down all te tunnles are going to be down?
> > >
> > > but in one of my case ldp goes down but te tunnels did not.
> > >
> > > Also I seee ldp neigbor is up for 4 hours but mpls te tunnel up for 8
> > > hours.and 4 hours ago ldp went down.
> > >
> > > On Thu, Feb 2, 2012 at 1:18 PM, sundeep sadhwani <
> > > sundeep.sadhwani_at_gmail.com
> > > > wrote:
> > >
> > > > Hi Mustafa,
> > > >
> > > > RSVP is used for reservation of bandwidth in TE environment( i am
> > giving
> > > u
> > > > a very high level view). However plain MPLS-TE is not used in
> > production
> > > > scenario as SPs have MPLS-VPN as well. for that purpose we require
> LDP
> > as
> > > > well to distribute IGP labels that will be required for PE to PE
> > > > communication in case of MPLS-VPN.
> > > >
> > > > Regards
> > > > Sundeep
> > > >
> > > > On Thu, Feb 2, 2012 at 4:41 PM, Mustafa Yadav <
> mustafa.yadav_at_gmail.com
> > > >wrote:
> > > >
> > > >> HD0,
> > > >>
> > > >>
> > > >> In a cisco network I have seen mpls traffic engineneering tunnels
> are
> > > >> being
> > > >> used .So as far as I know rsvp must be configured .But I alos see
> that
> > > ldp
> > > >> is configured in all boxes.why is that?Is not rsvp enough for
> > > distrbuting
> > > >> labels?
> > > >>
> > > >>
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> --
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> Yours Friendly,
> H P HEMANTH RAJ
> CCIE#28593 (R&S)
> Cisco Systems
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