Route Selection
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... Routing policies that the architecture must support may be broadly
classified into transit policies and route selection policies
[Breslau-Estrin91, Estrin89 ...
... domains, the architecture
must support heterogeneous route selection policies, where each
domain can establish its own criteria for selecting routes. This
...
... neighbors. This is really just a corollary to the above; i.e., if we
allow route selection policy to be expressed for NR routes, we can
not assume all domains ...
... not assume all domains will apply the same policy. The support for
dissimilar route selection policies is one of the key factors that
distinguish inter-domain routing from intra-domain ...
... non-goal of the architecture to support
all possible route selection policies. For more on unsupported route
selection policies see Section 2.3.2 below.
...
... architecture to support
all possible route selection policies. For more on unsupported route
selection policies see Section 2.3.2 below.
...
...
1. Route selection policies contingent on external behavior.
The route selection process may be modeled by a function that
...
... 1. Route selection policies contingent on external behavior.
The route selection process may be modeled by a function that
assigns a non-negative integer to a route ...
... integer to a route, denoting the degree
of preference. Route selection applies this function to all
feasible routes to a given destination, and selects the route ...
... In Section 4 we describe additional services that may be provided to
support more adaptive route selection for special TOS [Footnote:
Adaptive route selection ...
... route selection for special TOS [Footnote:
Adaptive route selection implies adaptability only during the route
selection process. Once a route is selected, it is not going to be a
...
... TOS [Footnote:
Adaptive route selection implies adaptability only during the route
selection process. Once a route is selected, it is not going to be a
subject ...
... contrast to LS and distance vector which use a globally-defined
monotonically-increasing metric for route selection [Shin87].
...
... routing domains to have homogeneous
criteria (policies) for route selection, route selection policies
used by one routing ...
... domains to have homogeneous
criteria (policies) for route selection, route selection policies
used by one routing domain ...
... have its own view of what constitutes an optimal route. This view is
based solely on local route selection policies and the information
carried in the path attributes of a route ...
... path attributes of a route. PV standardizes only the
results of the route selection procedure, while allowing the
selection policies that affect the route selection to be non-standard
...
... results of the route selection procedure, while allowing the
selection policies that affect the route selection to be non-standard
[Footnote: This succinct observation is attributed to Ross Callon
(Digital Equipment Corporation).].
...
... aggregation of routing
information, no transit constraints, a single homogeneous route
selection policy across all the domains, and a single TOS, requires a
...
...
Supporting heterogeneous route selection and transit policies with
hop-by-hop forwarding and LS requires each domain ...
... domain to know all other
domains route selection and transit policies. This may significantly
increase the amount of routing information that must be stored by
...
... number of domains, then the storage could become unsupportable. In
contrast, support for heterogeneous route selection policies has no
effect on the storage complexity of the PV scheme (aside from simply
storing the local policy information). The presence of transit
...
... domain is distributed to adjacent
domains. In contrast, route selection with LS is decoupled from the
distribution of routing information, and has no effect on such
...
... constraints with LS may result in either reduced
connectivity or less information reduction, as compared with PV.
Aggregating heterogeneous route selection policies in LS is highly
problematic, at best. In PV, route selection policies are not
...
... Aggregating heterogeneous route selection policies in LS is highly
problematic, at best. In PV, route selection policies are not
distributed, thus making aggregation of route selection ...
... route selection policies are not
distributed, thus making aggregation of route selection policies a
non-issue [Footnote: Although a domain's selection policies are not
...
...
Even if all domains employ exactly the same route selection policy,
computational complexity of PV is smaller than that of LS. The PV
computation consists of evaluating a newly arrived route ...
...
Support for heterogeneous route selection policies has serious
implications for the computational complexity. The major problem
with supporting heterogeneous route selection ...
... route selection policies has serious
implications for the computational complexity. The major problem
with supporting heterogeneous route selection policies with LS is the
computational complexity of the route selection itself.
...
... with supporting heterogeneous route selection policies with LS is the
computational complexity of the route selection itself.
Specifically, we are not aware of any algorithm with less than
...
... hop-by-hop routing and heterogeneous
route selection policies. In contrast, PV allows each domain to make
its route selection ...
... route selection policies. In contrast, PV allows each domain to make
its route selection autonomously, based only on local policies.
Therefore support for dissimilar route selection policies has no
...
... its route selection autonomously, based only on local policies.
Therefore support for dissimilar route selection policies has no
negative implications for the complexity of route computation in PV.
...
...
As indicated above, support for heterogeneous route selection
policies, in view of its computational and storage complexity, is
impractical with LS hop-by-hop ...
... hop-by-hop routing. In contrast, PV can
accommodate heterogeneous route selection with little additional
overhead.
...
... NR
components, given the difficulty of supporting heterogeneous
route selection policies in NR.
...
... routing in the presence
of (a) flexible aggregation, (b) heterogeneous route selection
policies, and (c) incomplete or inconsistent routing information, we
...
... topology and policy) [Footnote: If SDR uses NR information then
operational status could be considered in some route selection.].
Consequently, it is possible for a source routing domain ...