The MPLS-OPS Archive

[Rajiv Asati <rajiva@cisco.com>]

[ccing the wider audience, as it might be useful to others as 
well.]

At 05:36 PM 7/21/2002, M. ELK wrote:
> Rajiv 
>  
> Million thncks for the explanation . 
> 1) 
> For MPLS VPN CSC-Ipv4BGP Label distribution 12.0(21)ST .   In
> page 28 under CSC-CE1 configuration , the interface ethernet4/0 (which
> is the interface connecting to CSC-PE1)  

Actually, it is the ethernet3/0 that connects to the CSC-PE1. Ehternet4/0
connects to the PE1 and hence, needs LDP to be configured.

So as per the topology:
CE1----PE1----CSC-CE1--------CSC-PE1---------CSC-PE2-------CSC-CE2-----PE2-------CE2

Here is how we deduce (by looking at the IP addressing i.e
pp.0.0.0/8):

CSC-CE1#
! 
interface Ethernet3/0 
 ip address pp.0.0.1 255.0.0.0 
! 

CSC-PE1#
! 
interface Ethernet3/1 
 ip vrf forwarding vpn1 
 ip address pp.0.0.2 255.0.0.0 
! 

> is config with A- " Mpls label protocol
> ldp" and B-"Mpls ip" . 
> is it mean that CSC-CE1 is actually starting LDP on this interface and
> actually  sending ldp hello packets on this interface .

So to design CsC, we have two options. We use 
 - either eBGPipv4+Label on the PE-CE
 - or IGP+LDP on the PE-CE.

IOS CLI will even prevent us configuring the both. ;-)

>  
> i guess that CSC-CE1 will be sending ldp hello packet to cater for the
> special case/topology that an ethernet interfac connecting to CSC-PE1
> could also be used to connect to PE1  (where CSC-CE1 and PE1 will
> have LDP session ) . 

Nope. That's not the case.

>  
> 2) 
> Under CSC-PE1 config (page 28 at the end) . 
> interface ethernet3/1 associated with VPN1 is not config with "mpls
> ip" .
> so how CSC-PE1 will consider it is ok to switch label packet to/from
> ethernet3/1  . 

Since CSC-PE1 is exchanging labels and prefixes with CSC-CE1 via eBGP,
configuring MPLS is not required.

> is it implicity with "nei pp.0.0.1 send
> label" ie: 
> pp.0.0.1 is routed to the connected netw pp.0.0/24 so interface 
> ethernet3/1 with ip address pp.0.0.1/24  is enabled for label
> switching . 

Yes. That's true. 

And if you had to do following:
"sh mpls int ethernet3/1 de".
You would see that the BGP tagging is enabled on the interface. 

Enabling MPLS on an interface could be done via number of way such as
configuring LDP, configuring TE, configuring MP-BGP (for Inter-AS) or
configuring eBGPipv4+label.

> is this the reason behind eBGP multihop
> between CSC-CE and CSC-PE is not supported as if ebgp is supported we
> could not relate the 
> "nei XXX send label" and a specific VRF interface  ??

You are right. 


>  
> 3)If  an interface is enabled for label switching  implicity by
> "nei xxx send label"  . 
>  
> Assume that CSC-CE1 have already another interface with LDP enabled 
> (the TDP/LDP process is started and LFIB is created) .
> could i config CSC-CE1 interface ethernet4/0 connecting to CSC-PE1
> without 
> A-  " Mpls label protocol ldp" 
> neither with  
> B-"Mpls ip" . 
>  
> and depend on "nei pp.0.0.2 send label" to enable label
> switching on 
> ethernet4/0 . 
> in such cases no ldp hello packet will be seen on ethernet4/0 . 
> is it correct . 

If I understand you correctly, then you have one interface (not
connecting to CSC-PE1) already enabled with LDP.
And you want to know whether you could configure eBGPipv4+label on the
PE-CE link i.e. ethernet4/0 and have MPLS get enabled on it.
The answer is YES.
And yes, no ldp hello will be seen on ethernet4/0 that connects to
CSC-PE1. LDP hello will be only sent on the interface on which "mpls
ip" is configured.

>  
> 4) MPLS VPN Inter-AS-Ipv4 BGP label distribution 12.0(21)ST state
> that  ASBR to ASBR connection could not be PPP encapsulated .
> Could U pls clarify why such restriction . 

I am not sure where this restriction came from. Let me take a look into
it and I will get back to you.

> is the POS fall under such restriction (since
> it is just PPP over Sonet ) 

Actually, POS is packet over sonet. :-)
you could have other encapsulation (that ppp) on the POS as well. 
For example, frame-relay over POS:
http://www.cisco.com/warp/public/127/frame_19180.html

> By analogy is it also applicable for CSC-CE1
> to CSC-PE1 ?? . 

I don't think that this restriction holds true. But as I said, I will get
back to you.


>     
> At the end ,thnck U very much for U time . 
>  
> Thncks very much for the help , at first glance the doc's seemed very
> usefull . i printed almost all and i will start to look at . 
> Hope it is ok if i contact U if anything is not clear for me .

Sure. I will be more than glad to help.

Are you planning to implement CsC in your network ?

Rajiv

 
Brgds

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