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Community Member

VPN route label, and PW

Bonjour,

In IP VPN, the VPN route label is an MPLS label, attached to a VRF.

In VPLS, the VPN route label is a PW label, attached to VSI.

Would you know why we can't use a PW label in an IP VPN?

Best regards,

Michelot

5 REPLIES
Hall of Fame Super Silver

Re: VPN route label, and PW

Hello Michelot,

actually the MPLS label space is only one for each node.

MPLS labels can be picked up by different signalling protocols from this single space and then advertised to peers in the appropriate sessions

in the case of EoMPLS pseudowire these labels are picked up and advertised by LDP over targeted LDP sessions

in the case of L3 MPLS VPN, MP BGP picks up one (or multiple ) labels per VRF site and will advertise them over VPNv4 address family to peers

All devices have to agree on the use of these service labels.

So when sending traffic to a specific PE node (external label pointing to device loopback) the internal service label is unique on that node and can be associated to an MPLS L3 VPN or to a pseudowire but not to both at the same time

Hope to help

Giuseppe

Community Member

Re: VPN route label, and PW

Hello Giuseppe,

Thanks for this reply.

> So when sending traffic to a specific PE node (external label pointing to device loopback)

> the internal service label is unique on that node and can be associated to an MPLS L3 VPN or

> to a pseudowire but not to both at the same time

Am I understanding correctly that?

For EoMPLS we have: ETH > PW (route label) > MPLS (tunnel label) > Transport layers

For IPoMPLS (RFC 4364) we have: IP > MPLS (route label) > MPLS (tunnel label) > Transport layers

So, my question was: why in IPoMPLS we don't have PW instead of MPLS for the route label?

Perhaps, the term MPLS for the VPN route label has evolved in PW after.

Thanks for an opinion.

Best regards,

Michelot

Hall of Fame Super Silver

Re: VPN route label, and PW

Hello Michelot,

real encapsulations on wire is:

>> For EoMPLS we have: ETH > PW (route label) > MPLS (tunnel label)  > Transport layers

L2 Frame -> MPLS label (IGP,LDP BGP to next-hop)| service label= Pseudowire

I don't know why in many references the order of labels is reversed but the external label changes at each hope

L3 VPN

Eth --- MPLS label (IGP,LDP BGP to next-hop) | MP BGP VPN label

PW stands for pseudowire and was developed for EoMPLS scenario

Hope to help

Giuseppe

Community Member

Re: VPN route label, and PW

Hello Giuseppe,

Thanks for your words.

Subject (1)

>>> For EoMPLS we have: ETH > PW (route label) > MPLS (tunnel label)  > Transport layers

> L2 Frame -> MPLS label (IGP,LDP BGP to next-hop)| service label= Pseudowire

> I don't know why in many references the order of labels is reversed but the external label changes at each hope

I agree that the external label is that one which change at each hope. So, I am used to write as above: (stable) PW over MPLS (modified hop to hop)

Perhaps, you are used to write: MPLS (modified hop-to-hop) over PW. Thus the client is below, crushed under all the layers. But, the result is same.

Subject (2)

> PW stands for pseudowire and was developed for EoMPLS scenario

It seems that a first RFC is RFC 3916 dated from september 2004.

PW was developped for ATM, FR, Ethernet: all L2, and also for CES.

Subject (3)

Perhaps, talking with you, I have an explanation for the difference between PW label and MPLS label for the route (the most iternal label).

RFC 3916 "These mechanisms (that is QoS mechanisms, DiffServ...) do not have to be defined in the PWE3 approaches themselves.

Best regards,

Michelot

Hall of Fame Super Silver

Re: VPN route label, and PW

Hello Michelot,

>> Perhaps, you are used to write: MPLS (modified hop-to-hop) over PW. Thus  the client is below, crushed under all the layers. But, the result is  same.

No, it is not the same.

I like to use the way the real encapsulation as it is on wire, and I personally don't like the other notation, there is a label stack and the inner label is that of the service and the external label in the encapsulation are usually created by different signalling protocols

If you make a packet capture you see the difference

A lot of presentations calls the external label in the encapsulation internal because it comes from an IGP

>> Perhaps, talking with you, I have an explanation for the difference  between PW label and MPLS label for the route (the most iternal label).

I hope so

There are many RFCs on the subject.

I think everyone agrees on the fact that pseudowire is related to L2 transport services

Hope to help

Giuseppe

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