IPv6 over MPLS 6PE/6VPE

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:2.2.2.2 in PE BGP table ? Why its prepending ::FFFF: before IPV4 next hop address ? Thx

BR//ZAMAN

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 2.5.5.2.

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!

Rene

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

BR//ZAMAN

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!

Laz

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

BR//ZAMAN

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:

Laz

Hi Rene,
Good day and hope you are save .

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

BR//ZAMAN

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:
https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r6-0/mpls/configuration/guide/b-mpls-cg60x-asr9k/b-mpls-cg60x-asr9k_chapter_01010.html#concept_FA2F48EE4A2044458FE25897118AFBA4

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!

Laz

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.

Laz

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

Hello,

I went through the lesson and I had the same question. Why we need a second label for 6PE since there are no VRFs involved?

The below link helped me a lot and it might help others as well.

1 Like

Hello Ilias

Thanks for sharing that, it’s a good addition to the answer. Your contribution is appreciated!

Laz

2nd video 6vPE is left only audio.

Hello Justin

I went in and checked and saw that I was able to have both audio and video on the 6VPE video, so it is likely some setting on your end. Are you experiencing this problem only on the second video or on both videos in the lesson? How about other videos on other lessons? Also, can you try to open the same page using a different browser? If the problem persists, let us know so that we can further troubleshoot the issue and help you resolve it.

I hope this has been helpful!

Laz

hmm weird idk what happened, but now it is working fine. This is usually on the application side when it happens. Maybe it was just a bug. I hope I didn’t waste too much of your time. It was only the second video . No other videos that I watched had that problem.

1 Like

Hello Guy

I’m not sure I completely understand your question. Can you rephrase it and also show us the particular configurations that you are confused about? Thanks!

Laz

Nevermind, I got it! Thank You

1 Like

i have a network running ipv6 however the mpls backbone is running ipv4 while every other devices are running ipv6 but i am finding it difficult to ping through end to end.

i need your help please.

Hello Adekunle

There may be several issues involved in the successful communication between devices across an MPLS infrastructure. In order to get this to work, you must employ some sort of tunneling so that your IPv6 traffic is tunneled over the IPv4 MPLS infrastructure. One way to do this is described in this lesson that shows how to successfully achieve this using 6PE/6VPE:

Let us know some more details about your setup and at what point you are having difficulty so that we can help you further.

I hope this has been helpful!

Laz