Subject: ce range in l2 mpls vpns

From: Juha Heinanen <[email-masked]>
Date: Thu, 23 Nov 2000 12:31:15 +0200

this may have been discussed already, but why does
draft-kompella-mpls-l2vpn-01.txt require that the ce is configured with
the ce id, the ce's range and all labels in that range?  why can't the
ce dynamically add a new neighbor when it learns about a new label via
lmi, ilmi, or a corresponding mpls protocol?

i'm asking this because the proposed practice would be a step backwards
from how people have been running atm or fr vpns for years using cisco
cpe routers, where the only thing i need to configure is the
(sub)interface and an ip address.

here is a frame relay example:

interface Serial <number>
  ip address <address> <mask>
  encapsulation frame-relay IETF 
  ip ospf network point-to-multipoint 

and here is an atm example:

vc-class atm broadcast 
  broadcast 

interface ATM <number>
  atm pvc 2 0 16 ilmi 
  atm ilmi-pvc-discovery subinterface 

interface ATM <number>/<number> multipoint 
  ip address  address mask 
  ip ospf network point-to-multipoint 
  class-int broadcast 

dlcis or atm vcs of the other sites are learned dynamically via lmi or
ilmi.  as you see in above, the cpe doesn't even need to be configured
with its own ce id.

-- juha

---

From: Kireeti Kompella <[email-masked]>
Date: Thu, 23 Nov 2000 13:30:27 -0800 (PST)

Hi Eduard, Juha,

> This is indeed a bit confusing. 

Yes, sorry, my fault.  When the text says "CE configuration", what
is meant is "per-CE configuration on a PE" ...

> As far as I understand (Kireeti: correct me if I'm wrong here) the
> parameters are actually *configured* on the PE.

Correct.

> However, the CE should know
> about this.

How much the CE needs to know can vary from as little as "this interface
(to the PE) is Frame Relay, and the PE will tell me which DLCIs are up,
and inarp will tell me addresses/OSPF will tell me routes" to "for this
interface, this is the list of DLCIs and corresponding IP addresses" if
LMI/inarp is not supported.

> In particular the CE configuration should reflect the same logic
> that is applied by the PE in mapping CE-to-CE circuits to eachother. This is
> the algorithm described in Section 4.3.1. When CE and PE configuration are
> not aligned on this point, the CE may expect to connect to one site on a
> particular circuit, while the PE actually connects it to another one.

If the CEs are running (say) OSPF, and learn routes dynamically,
they should not really care whether DLCI 56 or 93 gets them to a given
site.  However, the network operator may want to know this.

> I think the text should say that the parameters are configured on the PE,
> and that the CE should know about this / reflect this in it's configuration.
> Currently, it is described in the exact opposite way. Also it makes less
> sense to configure it on the CE since there is no interaction between PE and
> CE to exchange this information.

The next version will state this more clearly.

Kireeti.