Specifications

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Other features supported by the JUNOS routing policy server are :
§ Policy Arithmetic
Provides the ability to do arithmetic in policy. For example this feature lets
customers add an offset to the MEDs received from a particular peer. This
feature provides the ability to add or subtract values from :
o Metric
o Preference
o Tag
o Color
o Local-preference
Any place you can set these items, you can now add or subtract relative
amounts too, so that values behave like gauges with a minimum and a
maximum. An example of how this is configured is provided below :
[edit policy options]
policy-statement math-is-easy {
from {
protocol rip;
neighbor 1.2.3.4;
}
then {
metric add 2;
}
§ Macros to represent lists of prefixes
An operator always needs to configure the static routes for a statically-routed
customer or the route filters for a dynamically-routed customer.
However, if that operator needed to configure source address verification
lists then the operation was to duplicate very similar information in the
configuration.
Now the operator could configure a “macro” containing the list of prefixes
used by the subscriber, then the operation could use the macro in both the
static routes (or router filters) as well as in the source address verification
packet filter -- thus minimizing duplicated information on the configuration
and making maintenance easier.
Prefix-lists can be defined either under policy-options or under firewall filters.
The user can create macros containing lists of prefixes for source address
verification lists or policy router filters. He can use the same macro for
packet filtering and route filtering. This is the way Junos allows to do
reverse-path-forwarding ACL checks for address verifications. Instead, the
user can create a macro containing a list of prefixes.
§ AS Path Range Expressions
Whenever a single AS number appears in an AS-path regular expression,
the user can also specify a range of AS numbers to match. This is done by
separating the two AS numbers with a '-' character, as per the example
below :
policy-options {
as-path cartman 123-125;
}
which matches a route with an AS path of 123, 124 or 125.
The range operator has highest precedence : 123-125* means 0 or more
occurrences of any AS number between 123 and 125.
§ Policy-based LSP Selection
Normally when there are several routes with a particular BGP nexthop to
which there are more than one MPLS LSP and per-prefix load balancing is
being used, Junos chooses the nexthop for a given route randomly. The user
can exercise some control over which LSP gets used for a given route by
specifying a prefix-list when configuring an LSP. Policy-based LSP Selection