[Openv6] APONF and its relationship to AECON and SFC
Tom Taylor <tom.taylor.stds@gmail.com> Sun, 13 July 2014 10:44 UTC
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Date: Sun, 13 Jul 2014 06:43:55 -0400
From: Tom Taylor <tom.taylor.stds@gmail.com>
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Subject: [Openv6] APONF and its relationship to AECON and SFC
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Having reviewed AECON and SFC documentation, I reread the APONF problem statement to more clearly understand exactly what that document is proposing. This note starts by laying out my understanding of APONF, and then showing its relationship to the other two initiatives. At an appropriate time I could follow up this note with proposed changes in text for the problem statement, but I imagine it would be a while before we get down to that sort of detail. At this point, the APONF proposal appears to me to be one for a new management protocol to add to COPS, SNMP, and NETCONF. I wouldn't mind having my think straightened out if that is not the case. USE CASE EXPECTATIONS ===================== First, a review of what the APONF use case documents expect of APONF. In summary, the use cases expect the following: (1) Collection of current configuration and policy from network devices. The most demanding statement of this requirement is provided in the SAVI use case, draft-bi-aponf-sdsavi-00.txt: <quote> 3.1. Element View Collection From the interfaces provided by APONF, the SAVI solution at first collects the related elements. An incomplete list contains: the address assignment mechanisms and their priorities, the topologies, the roles of network devices(e.g., host, DHCP server/relay, switches), the address transition mechanisms, the supported local/ cross-network mobility mechanisms, the tunnel/encapsulation/ decapsulate configuration and mechanisms, the address authentication mechanisms, etc. </quote> (2) Identification of the devices affected by a specific service instance being processed by a specific management application. (3) Conveyance of information generated by individual management applications to the affected devices. This information can vary in scope from link-related parameters for algorithms running on the network devices, through per-subscriber and per-flow policy. A HIGH LEVEL PICTURE ==================== The high-level picture of APONF operation is much simplified from my previous view. O /|\ /_\ ---------------------------------- | Network management | | application | | (SAVI, OpenV6, inter-DC, etc.) | | APONF mapping? | ---------------------------------- | /\ APONF Network transport Policy & data | configuration | updates | \/ | ------------------- | Network devices | | | ------------------- RELATIONSHIP TO AECON ===================== I think previous discussion has established that there is no necessary relationship between APONF and AECON. Possibly APONF could be used to place policy on devices relating to specific AECON code points. RELATIONSHIP TO SFC =================== SFC has the potential to be as central to packet processing within an individual domain as digit translation was to call processing in circuit switches. The Service Function Chain potentially includes encapsulation, decapsulation, and IP header modification, which in turn require resubmission to the SF Forwarding Function to determine the next step in the processing chain. The SFC architecture (draft-merged-sfc-architecture-00, not yet a WG document) is illustrated in the following figure: o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +--------------+ +------------------~~~ . | Service | SFC | Service +---+ +---+ . |Classification| Encapsulation | Function |sf1|...|sfn| +---->| Function |+---------------->| Path +---+ +---+ . +--------------+ +------------------~~~ . SFC-enabled Domain o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A more detailed breakdown of the right-hand-side of this figure follows. +----------------+ +----------------+ | SFC-aware | | SFC-unaware | |Service Function| |Service Function| +-------+--------+ +-------+--------+ | | SFC Encapsulation No SFC Encapsulation | | | SFC Encapsulation +---------+ +------------------+ +-------------|SFC Proxy| \ / +---------+ +-------+--------+ | SF Forwarder | | (SFF) | +-------+--------+ | SFC Encapsulation | +-------+--------+ | SFC Network | | Forwarder (NF) | +----------------+ | ... SFC-enabled Domain ... | Network Overlay Transport | _,....._ ,-' `-. / `. | Network | `. / `.__ __,-' `'''' APONF may complement SFC by providing the SFC Forwarder (SFF) with an up-to-date picture of available devices and their roles. The SFC charter leaves this point open: <quote> 4. Control Plane Mechanisms: A document will be developed to describe requirements for conveying information between control or management elements and SFC implementation points. All protocol extension work resulting from these requirements should be carried out in the working group responsible for the protocol being modified in coordination with this working group, but may be done in this working group under a revised charter after agreement with all the relevant WG chairs and responsible ADs. </quote> The first bullet of the APONF statement of requirements and objectives (Section 4) makes no sense as I read it: <quote> o) monitor and verify the freshness of the network service graph. </quote> A network service graph is information conveyed in the SFC Encapsulation, which is implanted by the Service Classification Function and updated by the Service Function or its proxy (see above). The relationship between network service graphs (AKA Service Function Chains) and classifying information is something that could be updated by an APONF management application, but I can't see that as changing (losing freshness) without management action. Tom Taylor