The MPLS-OPS Archive

["Shailendra Gupta" <shailendra.gupta@estelcom.com>]

Dear Dominiciano

I appreciate your valuable feedback & correction, as mentioned before I am
doing test and would share the results.

Shailendra

----- Original Message ----- 
From: "Domiciano Alonso Fernández" <daf@ttd.net>
To: "Shailendra Gupta" <shailendra.gupta@estelcom.com>
Cc: "mplsrc" <mpls-ops@mplsrc.com>
Sent: Friday, February 20, 2004 2:22 PM
Subject: Re: [MPLS-OPS]: TTL value of VPN Label at the Ingress


Hello,
I quite disagree. Actual implementations (IOS & JunOS) copy the TTL
field whenever they stack a new label, and the LSR's only decrement the
outer label TTL and copy the outer TTL to the inner label when popping a
label.
See section 2.4 of RFC 3032: MPLS Label Stack Encoding

   The "incoming TTL" of a labeled packet is defined to be the value of
   the TTL field of the top label stack entry when the packet is
   received.

There's also work in progress to support both models. See IETF RFC 3443:
Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS)
Networks,

Regards


Shailendra Gupta wrote:

> Dear Daipan
>
> Yr question is quite interesting, while I will check this in our real
> environment but based on my present knowledge, I feel that TTL Value
> is copied on to VPN Label but not IGP Label.
>
> Rgds
>
> Shailendra
>
>     ----- Original Message -----
>     From: Daipayan Kar Choudhuri <mailto:daipayan@deccanetworld.com>
>     To: Kumar S <mailto:ps2kumar@yahoo.com> ; mplsrc
>     <mailto:mpls-ops@mplsrc.com>
>     Sent: Friday, February 13, 2004 11:01 AM
>     Subject: Re: [MPLS-OPS]: TTL value of VPN Label at the Ingress
>
>
>     Hi Shailender,
>                            Thanks for your mail . For normal MPLS
>     forwarding the IP TTL is copied in the MPLS header after
>     decrementing it by one. My question is who should carry this TTL
>     value in case of L3VPN ,the IGP label or the VPN Label ?
>
>     Regards,
>     Daipayan
>
>
>         ----- Original Message -----
>         From: Kumar S <mailto:ps2kumar@yahoo.com>
>         To: Daipayan Kar Choudhuri <mailto:daipayan@deccanetworld.com>
>         ; mplsrc <mailto:mpls-ops@mplsrc.com>
>         Sent: Saturday, February 07, 2004 5:07 PM
>         Subject: Re: [MPLS-OPS]: TTL value of VPN Label at the Ingress
>
>         Hi Daipayan,
>         Unlike L2 VPN TTL need to be propagated through MPLS core
>         incase of L3 VPN. TTL value of the IP field has to be copied
>         to the MPLS label during label imposition at the ingress
>         router as is the case of normal MPLS path.
>
>         The reason why RFC specifically says 2 is added in TTL field
>         to the VC label in case of L2 VPN is L2 VPN is a pseudo wire
>         service between customer edge devices and is emulating some
>         layer 2 service. But this is not the case with L3 VPNs where
>         L3 routing in the core is always assumed by Customer.
>
>         Regards
>         Shailender
>
>         Daipayan Kar Choudhuri <daipayan@deccanetworld.com> wrote:
>
>             Hi all ,
>                        I have a query regarding the VPN Label value
>             for L3VPN . What should be the TTL value for the VPN label
>             at the ingress PE ?  As I understand from the martini
>             draft for L2 Transport  the TTL value of the VC label is
>             set to 2 at the ingress but RFC 2547 does not discuss
>             about the TTL value of the VPN Label at the ingress .
>             Please throw some light on this.
>
>             Regards,
>             Daipayan
>
>
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-- 
Domiciano Alonso Fernández
Conmutación IP
Ingeniería de Red
Telefónica Data España



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