IPv6 over MPLS 6PE/6VPE

This topic is to discuss the following lesson:

Continuing the discussion from IPv6 over MPLS 6PE/6VPE:

hello sir I want to run this tutorial on GNS3, what type of IOS cisco is suitable for ipv6-over-mpls-6pe-6vpe configuration?


what is the send label command do? is it allowing the PE routers to add the transport label and the VPN label to IPv6 prefixes and then forward to other PE routers?

Hello Tuong

The neighbor send-label command is used to enable a router to distribute MPLS labels along with IPv4 routes to a peer router. When using IPv6 the command can be used in address family configuration mode, to bind and advertise IPv6 prefix MPLS labels.

For more information, you can take a look at the following link:

I hope this has been helpful!


Hi Guys - quick question - is dual stack in terms of IPv6 simply running v4 and v6 addresses on the same interfaces? Cheers - Gareth.

Hello Gareth

The term “dual stack” can mean several things depending on the context. In general, the term means that a single device is running both IPv4 and IPv6 simultaneously. On a host with one NIC, this means that the NIC has both an IPv4 and IPv6 address. On a router, this could mean that a single port has both an IPv4 and IPv6 address, or, as is the case in this specific lesson, it simply means that the same device is running both IPv4 and IPv6 simultaneously, but not necessarily on the same interface.

I hope this has been helpful!


Thanks Laz - good to know that it’s just a generic term.

1 Like

Dear Rene,

How are you ? After long time I am here . I didn’t find the below question answer …Please help me to clear .

  1. Why VPN label is needed in 6PE solution. I think only IPV4 LSP is enough . Please clear me if any logic here
  2. Why next hop is showing like this ::FFFF: in PE BGP table ? Why its prepending ::FFFF: before IPV4 next hop address ? Thx


Hello Zaman,

It’s all good here, busy as always :grin: How are you?

The VPN label solves the same issue as with “regular” MPLS VPN:

The VPN label helps the PE router to figure out to which RT/VRF the packet belongs.

This is the IPv4-mapped IPv6 address. You can read more about it in RFC 4291 under section

The first 80 bits are zeroes, then 16 bits ones (FFFF in hexadecimal). The remaining 32 bits are for the IPv4 address. This is how we show embedded IPv6 in IPv6 addresses or when we want to present an IPv4 address in IPv6 format.

Hope this helps!


Dear Rene,
I understand , The VPN label is needed to forward traffic to particular VRF .But In 6PE there is no VRF Scenario. Its Plain L3VPN .So why we need it ?Thx


Hello Zaman

You are correct that in the 6PE scenario, there is no VRF, but the global routing table is used. When you say that the IPv4 LSP is enough, you are correct, however, the point of the implementation of these solutions is to allow for IPv6 customer sites to run over an IPv4 MPLS infrastructure to function “as is”. So the VPN label, which is part of the initial MPLS VPN infrastructure must be there so that the core network can function. Note that the next hop advertised by the PE router for 6PE prefixes is still the IPv4 address that is used for IPv4 L3 VPN routes. A value of ::FFFF: is prepended to the IPv4 next hop, which is an IPv4-mapped IPv6 address.

You can find out more detailed information about this at the following Cisco documentation:

I hope this has been helpful!


Hi Laz ,
Still I can’t understand the logic behind the use of VPN label for 6PE scenario.Can you please help to understandable it again ? Appreciate your very nice cooperation as always .Thx


Hello Zaman

The truth is that I spent quite a bit of time reading through various Cisco documents, trying to get a clearer answer for why the VPN label is being used. The truth is that routing could successfully take place without it, as you mention. But when all else fails, talk to Rene or read the RFC :stuck_out_tongue_closed_eyes:. So I talked to Rene and he referred me to the RFC. It specifically states:

While this approach could theoretically operate in some situations
using a single level of labels, there are significant advantages in
using a second level of labels that are bound to IPv6 prefixes via
MP-BGP advertisements in accordance with [RFC3107].

This has been taken from page 5 of RFC4798 which describes 6PE, and it further describes the advantages of keeping the VPN label.

I hope this has been as helpful for you as it has been for me! :sunglasses:


Hi Rene,
Good day and hope you are save .

Is LDP can generate label for IPv6 prefix of IGP ??


Hello Mohammad

LDP can indeed generate a label for IPv6 as it has been updated to support IPv6 as can be seen in this Cisco documentation:

As stated in this documentation:

For the control plane, the underlying address family can be either IPv4-only, IPv6-only or both. Whereas for the LSP setup, an LSP is setup for IPv4 or IPv6 FEC prefix.

However, keep in mind that this particular lesson deals with allowing customers to use IPv6 addressing while keeping the core addressing of the MPLS network using IPv4. As described above, MPLS, and LDP natively support IPv6 in the whole infrastructure.

I hope this has been helpful! Stay healthy and stay safe!


Hi, there.
Not really a question but just a comment in regards to the second video (6vPE). The voice is audible on the left channel only. It is still fine but probably worth to reupload the video with fixed voice track.
Thanks for the content :slight_smile:

Hello Denis

Thanks so much for mentioning this. I’ll let Rene know.


Thanks @denis.grinceac, I’ll fix the video.