Marco,

> 2018/03/07 18:41、Marco Liebsch <marco.lieb...@neclab.eu>のメール:
> 
> Satoru,
> 
> since I read this at different places, let me ask one clarifying question 
> about the stateless motivation: 
> 
> I see that for SRv6 you may not need a state at the egress (at least not for 
> traffic forwarding) but for
> Uplink/Downlink (UL/DL) you need a state at both edges of the communication 
> since the DL egress
> serves as uplink ingress, correct?

2x unidirectional tunnels to form bidirectional paths require 4 states in total 
at both the ingress and egress.
In SR case it requires just 2 states at the ingresses for both directions.

Cheers,
--satoru



> 
> marco
> 
> 
> -----Original Message-----
> From: dmm [mailto:dmm-boun...@ietf.org] On Behalf Of Satoru Matsushima
> Sent: Dienstag, 6. März 2018 17:23
> To: Tom Herbert
> Cc: dmm
> Subject: Re: [DMM] Fwd: I-D Action: draft-ietf-dmm-srv6-mobile-uplane-01.txt
> 
> Hello Tom,
> 
>>> A Big progress is that the draft supports interworking with GTP over 
>>> IPv6 in addition to GTP over IPv4.
>>> And we have made change SRv6 function to IPv6 encapsulation with SRH 
>>> instead of SRH insertion by default.
>>> 
>> 
>> Hi Satoru,
>> 
>> If there are no intermediate hops od SIDs being set when encapsulating 
>> would a SR header still be needed or could this just be simple IP in 
>> IP encpasulation?  If is no SR header then it's possible that ILA 
>> might then be used to completely eliminate the encapsulation overhead.
> 
> I think you’re right. You would find that case in the draft as ‘Traditional 
> Mode’ which is equivalent with traditional GTP-U case. You seem you say ILA 
> is also equivalent with that mode. In addition, this draft introduces 
> ‘Enhance Mode’ to cover more advanced cases.
> 
> IMO SR is designed not to maintain path states except at an ingress node. So 
> the packet need to preserve original DA in the header that keep the egress 
> node in stateless. It would be great if ILA is designed in the similar 
> concept as well.
> 
> If it’s not, it looks a kind of tradeoff, between reducing the overhead and 
> keeping the statelessness. It’s not apple-to-apple comparison. To decide to 
> choose which one need to be prioritized would depend on each deployment case 
> in operators IMO.
> 
> Cheers,
> --satoru
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