Seg6 tunnel support

[Pier Luigi Ventre]

Hi all,

I was trying to create a segment routing v6 tunnel (seg6) with pyroute2 library but my tentative failed.

With ip route command is possible to create a tunnel in this way:

ip -6 route  add 2001:0:0:10::2/128 encap seg6 mode encap segs 2000::5,2000::6 dev eth0

Instead, this is what I did with my example script:

# Get iface

idx = ip.link_lookup(ifname=iface_name)[0]

# create SR tunnel 2001:0:0:10::2/128 encap seg6 mode encap segs 2000::5,2000::6 dev hnyc-eth0

ip.route(

'add',

dst='2001:0:0:10::2/128',

oif=idx,

encap={'type': 'seg6', 'mode': 'encap', 'segs':['2000::5', '2000::6']}

)

# release Netlink socket

ip.close()

Running this script adds a new static route for 2001:0:0:10::2/128 but not the expected tunnel, it looks like the encapsulation seg6 is silently discarded.

If I am right, I would like to add the support for seg6 tunnel mode to pyroute2 library, can someone point me where to start ?

Thanks

Pier

[Peter Saveliev]

There is an issue with seg6 encap, since the current code tries to work with any encap as with MPLS.

I'll try to play with it on the weekend.

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[Pier Luigi Ventre]

Hi Peter,

thanks for your prompt reply. In the meanwhile, could you kindly point me where to give a look in the library just to understand how encap

works ?

Thanks

Pier

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[Peter Saveliev]

https://github.com/svinota/pyroute2/blob/master/pyroute2/netlink/rtnl/rtmsg.py#L99

RTA_ENCAP points to `encap_info`, that should be a class (simple mapping) or a method (conditional mapping). It is a method now, but ut does no choice, simply returning `mpls_encap_info` class.

The rtmsg messages with RTA_ENCAP have RTA_ENCAP_TYPE that should be used as the condition to choose the way to decode the RTA_ENCAP NLA, but the issue is that it goes after RTA_ENCAP, thus the RTA_ENCAP decoding should be properly postponed until RTA_ENCAP_TYPE is met in the NLA chain.

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[Pier Luigi Ventre]

Thanks a ton !!!

Pier

[Peter Saveliev]

I prepared the code to support different lwtunnel types — https://github.com/svinota/pyroute2/commit/74db7d344f8dba8cd81f1713f77b5dafbb0fb579

So you can try to play with it already. I will also, but on the weekend.

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[Pier Luigi Ventre]

Hi Peter,

thanks for the commit. I was playing a little bit with code, now the technical difficulties for me are how I can encode this (I did not have too much time to dig into the code of pyroute2 library):

https://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git/tree/include/linux/seg6_iptunnel.h

Do you have any suggestion for me ? I was looking MPLS code but MPLS encapsulation is managed in a different way and uses different structures.

Thanks

Pier

[Peter Saveliev]

I committed a stub code for the NLA. Now we should decode the SRH structure.

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[Pier Luigi Ventre]

Hi Peter,

thanks for the commit. Starting from your code I was able to create a seg6 tunnel, the change is very quick and dirty (for now) but I think I can finish the work with the right suggestions.

The question is, do you plan to work on this in the next future or do you want me finish the patch ? If yes, how do you want to proceed ? PR on github ?

Thanks

Pier 

[Peter Saveliev]

Open a PR, please, we'll discuss the code on GitHub. You know how to work with SRH, I know the library, we'll get it working in the right way.

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