Subject: Re: [MPLS-OPS]: Definition of LIB and LFIB

From: "wu min" <[email-masked]>
Date: Thu, 18 Apr 2002 17:39:18 +0000

Hi,

In my opinion LFIB and LIB mean the same. LFIB/LIB contains information
as what Johannes listed. However I think I have encountered a reference 
which did not treat them as the same. In my opinion the reference refers LIB 
as a pool of labels that an LSR may use for label binding. The pool may 
contain several sets of valid label range.

I might be wrong here, but I think they are used inconsistently. Here are 
some references that you might want to see for yourself the usage of the 
terms LFIB and LIB:
1. http://students.cs.byu.edu/~cs460ta/cs560/slides/mpls-osbourne.ppt
2. http://flower.ce.cnu.ac.kr/~fog1/mns/mns1.0/MNS_v1.0_arch.pdf

Another term that is commonly used is FIB. IMHO, FIB is the normal L3 
routing table.

Other documents use ILM(Incoming Label Mapping), FTN(FEC-to-NHLFE), and 
NHLFE(Next Hop Label Forwarding Entry) to mean somewhat finer detail of 
LFIB/LIB.

Ignore this message if am incorrect at all.

-Tze Ven

>Roger Williams wrote:
>Johannes, it is my understanding that the LFIB contains what is
>actually being used to forward packets via label swapping, whereas the
>LIB contains all possible routes (generated by the underlying routing
>Link State Protocol) with labels already assigned (assuming frame mode
>MPLS). The LFIB is the outcome of an OS decision as to which route
>really is the Shortest Path. LFIB has only labels and interface
>information, with no IP information. The LIB has IP information, label
>and interface information, but no indication of which is the shortest
>path to the given destination.

>Any route in the LFIB will also be in the LIB, but not the other way
>around. The LFIB is a subset of the LIB, based on SPF algorithm
>calculation.

>Johannes wrote:
>I have found out that Label Forwarding Information Base (LFIB) is a
>subset of Label Information Base (LIB). I have not been able to find
>out exactly what information these two information bases contain.
>
>So far I found out LFIB contains:
>    -          Incoming Label
>    -          Outgoing Label
>    -          Next Hop
>    -          Outgoing Interface
>
>1. Is this correct and are there any other fields?
>
>I have not found any content specification for LIB.  RFC 3036, LDP
>Specification, explain that this information base contains, among
>other things, address prefix.
>
>2. What is address prefix?
>
>I assume this address is from the Forwarding Equivalence Class (FEC).
>3. Is this prefix also in the LFIB?
>4. What other parameters are in the LIB in addition to Incoming
>label, outgoing label and Interface?
>
>These should be explained in detail in RFC's but I've not found any
>information at IETF on this subject at all.

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Subject: Re: [MPLS-OPS]: Definition of LIB and LFIB
From: Roger Clark Williams <[email-masked]>
To: [email-masked]
Date: Wed, 17 Apr 2002 10:18:34 -0400

Johannes, it is my understanding that the LFIB contains what is actually
being used to forward packets via label swapping, whereas the LIB
contains all possible routes (generated by the underlying routing Link
State Protocol) with labels already assigned (assuming frame mode MPLS).
The LFIB is the outcome of an OS decision as to which route really is the
Shortest Path. LFIB has only labels and interface information, with no IP
information. The LIB has IP information, label and interface information,
but no indication of which is the shortest path to the given
destination.

Any route in the LFIB will also be in the LIB, but not the other way
around. The LFIB is a subset of the LIB, based on SPF algorithm
calculation.

Roger Williams

At 03:02 PM 4/17/2002, you wrote:

Hi,

I have found out that Label Forwarding
Information Base (LFIB) is a subset of Label Information Base (LIB). I
have not been able to find out exactly what information these two
information bases contain.

So far I found out LFIB contains:

-          Incoming
Label

-          Outgoing
Label

-          Next
Hop

-          Outgoing
Interface

1. Is this correct and are there any other
fields?

I have not found any content specification for
LIB.  RFC 3036, LDP Specification, explain that this information
base contains, among other things, address prefix.

2. What is address prefix?

I assume this address is from the Forwarding
Equivalence Class (FEC).

3. Is this prefix also in the
LFIB?

4. What other parameters are in the LIB in
addition to Incoming label, outgoing label and Interface?

These should be explained in detail in RFC's
but I've not found any information at IETF on this subject at
all.

Any answers will be appreciated. The questions
have been enumerated.

Best regards,

Johannes Vea

Hallstein Lohne

Agder University College, Norway

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---

From: "wu min" <[email-masked]>
Date: Fri, 19 Apr 2002 13:13:09 +0000

Hi,

>Roger Williams wrote:
>Tze, you may be correct, but Cisco says otherwise, at least in their
>training material. The LFIB is derived from the LIB, it is a subset of
>the LIB. Also the LFIB contains no IP information whereas the LIB does
>hold IP information. Cisco says the LFIB is generated when the actual
>shortest path to a destination is chosen. Hence, in the LFIB there
>will be one label pair for a destination (or FEC), whereas the LIB
>holds all possible paths to the destination.
>
>All this is based on the MPLS Tech Essentials, AMVS, MPLS
>Implementation, and VPNSC courses as issued by Cisco. Do I have any
>*real* proof? Not really, I'm just passing on what they say and what
>shows up in the various "show.." commands.

Yeah, I must admit that you are right about it. From the way RFC3036 
explains about LIB in section 2.7., it seems to agree with what you have 
just mentioned as it pointed out that when an LSR operates in downstream 
unsolicited mode, it would keep a collection of label binding info that it 
has learned in the LIB. When a label is needed, it will first consult the 
LIB to retrieve one to be used for forwarding (which I presume that it meant 
LFIB). I believe LIB is only significant when operating in such mode with 
liberal label retention mode combined.

I also agree with Johannes that no clear defination of such terms are widely 
available. It is also not listed under MPLS Acronym Dictionary in 
http://mplsrc.com/dictionary.shtml web page.

Thanks for this constructive argument.

-Tze Ven.

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---

From: "wu min" <[email-masked]>
Date: Fri, 19 Apr 2002 13:13:09 +0000

Hi,

-Tze Ven.