[Casm] Comments on CASM documents
Ignas Bagdonas <ibagdona.ietf@gmail.com> Thu, 02 March 2017 12:48 UTC
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From: Ignas Bagdonas <ibagdona.ietf@gmail.com>
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Date: Thu, 02 Mar 2017 12:48:35 +0000
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Subject: [Casm] Comments on CASM documents
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Hi there. An assorted list of comments on all 5 of CASM-related documents. The focus of the documents seems to be on BNG-type of SP access solutions. That is an important use case but not the only one that relies on (semi)dynamic allocation of address blocks. Prefix and address notations – an address is a form of prefix, it does not seem to be practical to single out a /32, /48, or /128 and treat them fundamentally differently. DHCP is not the only form of pool based address block allocation. What is meant by term ‘Interface’ here? There are intermixed interpretations of the term, in some places it tends to describe a programmatic interface and a protocol, in other places it is a conceptual control flow, in yet other places it seems to be a data model type of interface. What would be the deliverable of CASM solution? The value of address management systems is in ability to assign an arbitrary attributes to blocks of addresses which are not interpreted in any way by the address management system itself, instead they are kept and propagated as opaque metadata on which the consumers of such metadata can react. The concept of centralized IPAM – it is not practical to expect a truly centralized system of such impact and importance to be usable and resilient, there are many factors in network design (not all of them being only technical) that would mandate a distributed system instead. Something along the lines of RIR/LIR split. Standardized interfaces to IPAM – how much is it feasible and how much is it needed? The text can be interpreted as an attempt to define a standard interface based on a specific product implementation. IPAM access to network elements – there seems to be an assumption that IPAM element/system itself can interact with network elements. While it certainly can be the case, for practical deployments it would cause substantial manageability complexity increase by requiring coordination between IPAM and other entities that provide configuration and state information for network elements. Typically IPAM is seen as a backend database that does not directly have direct interface to network elements. Address block utilization feedback from network elements into IPAM system could be an area worth exploring. The overlay use case seems to assume that underlay infrastructure addressing is also coordinated by IPAM. That is not likely due to unnecessary manageability complexity increases. Not everything relies on DHCP, and there are different use patterns of DHCP in SP access compared to SP services compared to DHCP use in enterprise environment. The more generalized approach with flexible attributes would be preferred to a specialized use case scenarios targeted for a specific place in network. There are identifiers and address families other than IPv4 and IPv6 in use, and not excluding Ethernet tags, NVO3 VNIs, MPLS labels, identifiers related to VPN address families likely would be of value. There seems to be a distinction of interpretation between physical and virtual network elements – that does not seem to be practical. The examples of manageability constraints in use case examples can and in fact are solvable by automation even with existing systems without any new protocol work. IPAM as a function has close ties with operator’s internal systems and toolkits already. Use cases could try to cover traffic accounting integration into address management too. The fundamental question to me still remains on what is the scope of CASM – does it try to define CASM as an more abstract address management framework, or does it try to define CASM as a more concrete address management system? Ignas
- [Casm] Comments on CASM documents Ignas Bagdonas