Hi Robin

Here are some details related to existing Inter domain MPLS which has come a 
long ways since inception decades ago.  

Inter AS options A, B, C & CSC
https://tools.ietf.org/html/rfc4364#section-10

Inter AS option AB
https://datatracker.ietf.org/doc/draft-mapathak-interas-ab/

Inter AS Option A:  Back to back VRF native IP.  Subinterface VRF per customer 
VPN. LSP terminates on each ASBR PE router.  No BGP-LU (labeled switched 
unicast) which requires importing of loopback FEC of all PEs between each AS.  
Simple and works if isolation is required between providers.  Does not scale. 
Multicast Is simple as MVPN profiles do not need to match as PIM over the NNI 
inter AS link glues the two MVPN domains together.

Inter AS Option B: Segmented LSP with single VPNV4 BGP session over inter AS 
link.  Highly scalable.  RT filtering is enabled by default on all PEs so has 
to be disabled on ASBR PE. Retain RT policy applied can filter and RTs and 
don’t have to accept all RTs. Multicast MVPN profiles must match between SPs as 
recursive-FEC and this the LMDT(labeled multicast distribution tree) is end to 
end and not a segmented LSP as is with unicast.  For MVPN BGP-LU needs to be 
enabled for mLDP peer to come up for LDP router-id label binding.ASBR PE must 
maintain all the L3 VPN FIBs.  No BGP-LU (labeled switched unicast) which 
requires importing of loopback FEC of all PEs between each AS. 

Inter AS Option C: End to End LSP with BGP-LU (label switched unicast) enabled 
on inter AS link data plane path.  All SP PE loopback FEC destinations  must be 
exchanged imported between SPs and iBGP-LU PE to RR for SP loops exchanged to 
have label binding when advertised over eBGP LU inter AS. VPNV4 peering 
next-hop-unchanged for control plane update so end to end LSP can build between 
any to any PE between SPs. Multicast MVPN profiles must match between SPs as 
recursive-FEC and this the LMDT(labeled multicast distribution tree) is end to 
end and not a segmented LSP as is with unicast.  Option C offloads the ASBR PE 
having to maintain the L3 VPN FIB.

Inter AS Option AB Hybrid of Option A and B with single control plane VPNV4 
peer as is with Option B and VRF data plane isolation sub interfaces per 
customer VRF.  Scales well as control plane is provided via single BGP peer. AB 
provides additional security with VRF isolation feature.  No importing of PE 
FEC loopback as this is a segmented LSP with 3 segments. Multicast MVPN 
profiles must match between SPs as recursive-FEC and this the LMDT(labeled 
multicast distribution tree) is end to end and not a segmented LSP as is with 
unicast.  For MVPN BGP-LU needs to be enabled for mLDP peer to come up for LDP 
router-id label binding.ASBR PE must maintain all the L3 VPN FIBs.  

Of the 4 inter AS options available today with MPLS Option A very simple and 
seamless and works well if you have a minimal number of VRFs.  Option B and AB 
both are highly scalable and AB works well if security is a concern.  Option C 
is a good option for enterprises as well as service providers that have a close 
trust relationship.

In your introduction section can you provide some details I have mentioned of 
the existing MPLS inter domain options.  As you mentioned the importing of 
millions of prefixes that would only be with Option C and it would only be a 
million if each provider had a million PE loopback to import. 

As far as SR-MPLS since it’s reusing the MPLS IPv4 dataplane to provide BGP 
IPV4 IPV6 VPNV4 VPNV6 services for inter AS would that still have to use the 
traditional mpls inter as options.

As for SRv6 since it uses the IPv6 data plane as far as inter domain that can 
be stitched with SRv6 using Option B style but IPv6 dataplane in place of the 
MPLS topmost label. Then all BGP services IPV4 IPV6 VPNV4 VPNV6 would ride on 
top.  I guess you could do Option C style and advertise the PE FEC loopbacks 
between domains for an end to end SID list similar to an end to end LSP do the 
PSP PHP would not happen until you hit the last or next to last node in the 
chain of domains.

My guess is with both SRv6 and SR-MPLS you could literally take all for inter 
AS options and use them as the bottom service BGP label would be the same it’s 
just that you are swapping out the MPLS topmost label MPLS IPv4 data plane with 
SRv6 IPv6 data plane.

Thank you 

Gyan

Sent from my iPhone

> On Nov 8, 2019, at 11:38 AM, Lizhenbin <[email protected]> wrote:
> 
> Hi All,
> Until now there has been 7 SRV6 deployments in China. It is very typical for 
> Chinese operators to deploy services crossing multiple IP network domains.. 
> It is complex and time-consuming to use the traditional ways such as inter-AS 
> VPN based on MPLS. With SRV6, complexity of the service provision can 
> be reduced greately.
> The following draft proposed the advantages of SRv6 and incremental 
> deployment guidance. Then details of two SRv6 deployment cases from China 
> Telecom 
> and China Unicom are decribed. Hope it will be helpful for reference. 
> 
> Best Regards,
> Zhenbin (Robin)  
> 
> 
> 
> ________________________________________
> 发件人: [email protected] [[email protected]]
> 发送时间: 2019年11月4日 21:39
> 收件人: Lizhenbin; Feng Zhao; Xiaoyaqun; Jichun Ma; Pengshuping (Peng Shuping); 
> Chongfeng Xie; Hui Tian; Tong Li
> 主题: New Version Notification for 
> draft-tian-spring-srv6-deployment-consideration-00.txt
> 
> A new version of I-D, draft-tian-spring-srv6-deployment-consideration-00.txt
> has been successfully submitted by Shuping Peng and posted to the
> IETF repository.
> 
> Name:           draft-tian-spring-srv6-deployment-consideration
> Revision:       00
> Title:          SRv6 Deployment Consideration
> Document date:  2019-11-04
> Group:          Individual Submission
> Pages:          13
> URL:            
> https://www.ietf.org/internet-drafts/draft-tian-spring-srv6-deployment-consideration-00.txt
> Status:         
> https://datatracker.ietf.org/doc/draft-tian-spring-srv6-deployment-consideration/
> Htmlized:       
> https://tools.ietf.org/html/draft-tian-spring-srv6-deployment-consideration-00
> Htmlized:       
> https://datatracker.ietf.org/doc/html/draft-tian-spring-srv6-deployment-consideration
> 
> 
> Abstract:
>   SRv6 has significant advantages over SR-MPLS and has attracted more
>   and more attention and interest from network operators and verticals.
>   Smooth network migration towards SRv6 is a key focal point and this
>   document provides network migration guidance and recommendations on
>   solutions in various scenarios.  Deployment cases with SRv6 are also
>   introduced.
> 
> 
> 
> 
> 
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org.
> 
> The IETF Secretariat
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