Hi Robert, 发件人: [email protected] [mailto:[email protected]] 代表 Robert Raszuk 发送时间: 2014年4月21日 18:29 收件人: Xuxiaohu 抄送: Ron Parker; [email protected]; [email protected] 主题: Re: [sfc] Why Transport Dependence is deemed as a problem?//re: I-D Action: draft-ietf-sfc-problem-statement-04.txt
Hi Xu, How to simply use the MPLS label stack to realize the SFC has been described in http://tools.ietf.org/html/draft-xu-spring-sfc-use-case-00. Any comments are welcome. The draft says: "that packet, SN1 could further consume the metadata contained in the NSH and meanwhile decrease the service index value within the NSH by on e " I would observe after reading this draft that S x service node may not be capable of handling NSH of any sort (including SR header - be it MPLS label stack or IPv6 EHs) therefor much more then just decreasing the index value is required at SNx. It seems that to realize any service chain via most of today's service nodes a full removal of NSH and re-application is required at directly attached SNs. [Xiaohu] Your observation is correct. The SF proxy must strip the NSH and the SR header before sending the packets to the directly attached legacy service functions. When the packets was returned by service functions, the SF proxy must reimpose those headers on the packets. Meanwhile, the SF proxy must decrease the service index value by 1. That actually means that network needs to carry the state pretty much out of band. Such state could be carried within routing protocols (today BGP is used for that in L3VPN case) or by new overlay control plane - same as is used to carry the metadata. [Xiaohu] Did you mean that the metadata should be transferred through the control plane? Best regards, Xiaohu Cheers, R.
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