3.3.3 Bandwidth Overhead PV routing updates include fully-expanded information. Although TOSs may be encoded more efficiently with LS than with PV, link state information is flooded to all domains, while with PV, routing updates are distributed only to the domains that actually use them. In addition to flooding status updates to nearby nodes, we also want to provide more accurate route information for long distance communications that entails more than a few network hops. The distributed algorithm combines some of the features of link state with those of distance vector algorithms; in addition to next hop information, the NR component maintains path attributes for each route (e.g., the list of domains or routing domain confederations that the routing information has traversed so far). In addition, we intend for this architecture to support future network layer mechanisms, e.g., Clark and Jacobson’s proposal or Braden and Casner’s Integrated Services IP. Further work is needed to specify protocol in support for the NR component for ST-II.
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RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 4.0 Source-demand routing (SDR) Inter-domain routers participating in the SDR component forward packets according to routing information computed and installed by the domain that originates the traffic (source routing domain). RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 supported via two techniques: loose source-routing and route setup. RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 3.8 Summary Given the performance complexity issues associated with global routing, aggregation of routing information is essential; at the same time we have argued that such aggregation must be flexible. RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 Security Considerations Security issues are not discussed in this memo. In addition, if the domain does have sufficient information, it is possible that the quantity may be large enough to preclude storage and/or route computation in a timely fashion. Footnote: Although a domain’s selection policies are not explicitly distributed, they have an impact on the routes available to other domains. In contrast, with LS no such reduction is possible since each domain must know every other domain’s transit policies. Consequently, it is possible for a source routing domain to compute a route that is not operational at route installation time.
A source can also request notification if a previously-down link or node returns to operation some time after a requested route setup fails. The path attributes that are carried along with a route express a variety of routing policies, and make explicit the entire route to the destination. However these checks are much simpler than executing a full SPF algorithm. However, there are several reasons why NR and SDR would not use exactly the same routing information, even if they did use the same algorithm. However, the associated complexities of supporting transit policy constraints are noticeably higher for LS than for PV. Consistent network maps are not needed at each route server, since route computation precedes routing information dissemination. RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 topology maps at each node. RFC 1322 A Unified Approach to Inter-Domain Routing May 1992 criteria (policies) for route selection, route selection policies used by one routing domain are not necessarily known to other routing domains. Optionally, the detecting BR may include additional information about the state of other BRs in the same domain.
If demand driven route computation is not used for LS, then the size of the FIB would be the same for both LS and PV. Supporting heterogeneous route selection and transit policies with hop-by-hop forwarding and LS requires each domain to know all other domains route selection and transit policies. That is, the requirement to perform selective information hiding is unsatisfiable with LS hop-by-hop routing. To maintain the maximum degree of autonomy and independence between routing domains, each domain which participates in PV may have its own view of what constitutes an optimal route. Potentially the LS FIB may be smaller if routes are computed at each node on demand. For example, if we aggregate routing information of domains that do not share the same policy and TOS characteristics (i.e., services), then outside of the aggregate, only those services that are offered by all domains in the aggregate will be advertised.