The MPLS WG Archive

["Dominic-Savio, Patrick" <Patrick.Dominic-Savio@marconi.com>]

 

-----Original Message-----
From: Thomas Nadeau [mailto:tnadeau@cisco.com]
Sent: Monday, October 29, 2001 4:51 PM
To: Dominic-Savio, Patrick
Cc: 'mpls@uu.net'
Subject: RE: Question on tunnel Interface (w.r.t TE MIB)

 Note that this will be at the penultimate-hop, if that is

enabled.

Why should it be at the penultimate-hop ?. RSVP signalling goes all the way to the tail-end and the tail-end TE tunnel entry can be created there. (Also, penultimate-hop popping is optional).

        I was thinking of the LSR MIB this morning at the same time.
You are right.

Should a tail-end manual entry be made in the TE table ahead of time with

the mplsTunnelIsIf value set to TRUE?.

        Depends on your implementation. I suppose that you could manually

create such an entry, but I am not sure why. Some implementations represent

the tail of the tunnel the same way that other midpoints are represented (without

an ifIndex) except that the tunnelRole would be set to tail(3).

The reason to create this entry would be so that the user can set the mplsTunnelIsIf value to TRUE. So it is clear based on the configuration that this terminating tunnel will be a terminating point of an unidirectional interface.

If so, it does not seem like there is

a (documented) way to uniquely identify an incoming signalling message (for

tunnel termination) using the tail-end TE MIB specification. In other words

how do I match a user created tail-end configuration with (say) a RSVP

session that is terminating on this tail-end LSR.

        You should be able to figure this out given the RSVP-TE information

stored at the tail-end router. It should tell you that this RSVP-TE session

terminates at that LSR the same way that a mid-point LSR tells keeps

information about transit-sessions.

So you are saying that the terminating point of a tunnel interface is identified on the

terminating router based on the RSVP session information for that tunnel?.

        Most if not all MPLS implementations that I know of only require the operator
to configure the tunnel at the head end.  

 

But, if you want to treat a tunnel as a real interface (and assign IP addresses etc. to it at both ends) you will have to have interface configuration at both the head and tail ends. If you don't have a tail end interface configuration the only reason to use tunnel interfaces is probably to make the tunnel *look* like an interface on the head end router. This however means that you are treating it as an interface on one side and treating it as a simple terminating tunnel on the other side. This seems anomalous.

 

 If your implementation wishes to create an
interface for the tail end of the tunnel, it can do this based on the acceptance of
an RSVP-TE session at the tail point, or via manual configuration. However, making
this ifIndex consistent with the one at the head automatically is something that I think you
will have to do manually. 

 

I think you misunderstood, the actual value of the ifIndex is of no consequence, you just have to have a corresponding interface at the other end. 

But that is confusing if the user has to use the mplsTunnelTable to configure interface

capability on the head-end and use some other table to configure the interface capability

at the tail-end.

        How else would you propose getting that information to the tail? The only way I see
doing this is manually. I don't believe that there is a way of getting this information
to the tail using RSVP-TE, but I could be wrong. 

 

You don't have to get any additional information to the tail. For the tail-end configuration if you have two additional variables to specify the originating LSRid and originating tunnel index that should do it. With this information you can directly associate a tail-end configuration with a head-end configuration (which is already available at the tail-end through RSVP-TE signalling).

 

 

Thanks.

 
        --Tom

Let me give you an example, lets say you have router A and router B, with some intermediate hops (that are of no consequence).

There is a tunnel (tunnel index 1) with mplsTunnelIsIf set to TRUE originating on Router A and terminating on Router B. Also mplsTunnelName for tunnel 1 is "tunIntf1"

So you have an interface by the name of "tunIntf1" on Router A.

If you want to have an interface on Router B to receive packets sent from Router A on tunIntf1, how do you set it up ? and where do you specify the tunnel interface name on Router B?

Thanks

        --Tom

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Mathematics is the supreme nostalgia of our time.

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Mathematics is the supreme nostalgia of our time.