The MPLS WG Archive

["Santosh Gupta" <santoshg@daewoo.dti.daewoo.co.kr>]

Hi Eric
    Sorry for the goofup in name. It's actually Santosh. :)
Please c comments inline.

santosh
>
> To add to what Bob has said, one of your base
> assumptions is not necessarily correct.  Two LSR peers
> may be connected by more than one link.  Additional

fine

> interface addresses may be assigned to any interface
> of a router.  Also, an LSR that shares more than one
> link with a peer LSR will most likely use its router
> ID as its LDP ID (address portion) in order to avoid

I cant make out what do you mean by router ID. If a router has "n" cards
then it will have "n" IP Addresses corresponding to each card. Where is this
concept of router ID? Or is it the Internal representation (some no.
assigned ) at an LSR for the peer that you are refering to ?

> losing its LDP session as a result of removing the
> interface (from which it got the IP address) from
> service (i.e. - pulling out the interface card, or
> executing a "shut" command).  In any of these cases,
> it is some advantage to know additional addresses
> that apply to peer LSRs.
>
> --
> Eric Gray
>
> >
> >
> > Santosh,
> >
> > > Hello Bob
> > >     I have gone thru the section but still have a doubt.
> > Even in DownStream
> > > unsolicited Mode of label distribution, according to the
> > draft each LSR
> > > keeps a list of address prefix and their associated  (LDP
> > Identifier, label)
> > >
> > > LDP Identifier = Interface IP Address : Label Space.
> >
> > There is no guarantee/requirement that the first 4 octects of the
> > LDP Id is the IP address of the "Interface".
> >
> >
> > > Actually the Next hop address in the routing table will
> > exactly match the
> > > "Interface IP Address" specified in the LDP Identifier.
> > This "Interface IP
> >
> > I think you cannot guarantee that this is always true.
> >
> >
> > > Address" is the one directly connected to the peer.
> > > This is depicted below.
> > >
> > >                                             C
> > >                                       /
> > >                                 A   -----  | B |
> > >                                       \
> > >                                             D
> > >
> > > If B,C,D are directly connected to A then the "Interface IP
> > Address" that
> > > will be specified in the Address Message will be the same
> > as the Interface
> > > which A concludes from the HELLO message exchange. So what
> > is the need for a
> > > seperate "Address Message" altogether ?
> >
> > Please see comments above.
> >
> >
> > Bob
> >
> >
> > > One more thing, what is the use of specifying some other
> > "Interace IP
> > > Address" to A by B (say the interface of B with C ) if that
> > is not the
> > > directly connected interface to A?
> > >
> > >
> > > > Santosh,
> > > >
> > > > >     In draft-ietf-mpls-ldp-06.txt, there is an Address
> > Message and =
> > > > > Address Withdraw Message. I am not able to figure out
> > what purpose does
> > > =
> > > > > it serve. In the Hello packet that an LSR sends, it can
> > send the =
> > > > > Interface IP Address optionally. If it doesnt send then
> > the receiving =
> > > > > LSR can make out when it receives from the particular
> > socket. And what =
> > > > > do we gain if an LSR advertizes IP Addresses of other
> > interfaces also ?
> > > =
> > > > > The connection between 2 LSRs is anyway thru some
> > particular interface =
> > > > > and knowing the IP Address of other interfaces will be
> > of no use.
> > > >
> > > > See Section "LDP Identifiers and Next Hop Addresses".
> > > >
> > > > Bob
> > > >
> > >
> > >
> >
> >
>