BGP策略路由

if community matches-every(12:34, 56:78) then if med eq 8 then drop endif set local-preference 100 endif
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route-policy one set weight 100 end-policy route-policy two set med 200 end-policy route-policy three apply two set community (2:666) additive end-policy route-policy four apply one apply three pass end-policy
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Hierarchy and parameterization
• When any policy or set is modified, that change affects all instances of policy hierarchies that reference the modified policy or set. May impact performance! • Looping/recursion is not allowed • As many layers of hierarchy or parameters that you want • Parameters are passed by value only
• Human-readable
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BGP Bestpath
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This is an interactive session.... Don’t hesitate to stop me to ask a question!
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Why RPL?
• Improved Clarity
No Silently skipped statements. What you see is what you get!
if med eq 42 and next-hop in (1.1.1.1) then if med eq 10 and not destination in (10.1.3.0/24) or community is (56:78) if med eq 10 and (not destination in (10.1.3.0/24)) or community is (56:78)
if as-path in as-path-set-1 then drop endif
The if statement also permits an else clause, which is executed if the expression is false.
if med eq 150 then set local-preference 10 elseif med eq 200 then set local-preference 60 else set local-preference 0 endif
Designed to reduce some of the redundancy that is inherent in routemap configuration.
• RPL is a tool for implementing routing Policy.
RPL helps to manipulate route attributes and route selection.
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Hierarchical Policy
• A policy which refers to another policy with an apply statement.
• Use the policy:
router bgp 1 neighbor 2.2.2.2 address-family ipv4 unicast route-policy policy1 out
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BGP Policy
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Your Speaker
Nehal Bhau IOS-XR RPL & BGP Developer San Jose, CA nbhau@cisco.com
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Introduction to RPL
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route-policy one ($med) set med $med end-policy route-policy two apply one (10) end-policy
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RPL Building Blocks
• Simple if-then-else-elseif statements. • Boolean operators to combine multiple statements. • Hierarchical and parameterized policy definitions for modularity. • Unordered sets to form operand templates. • Protocol specific constructs: as-path, community, med, tag, metric etc.
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Configuring a route policy
定义策略！
• Define the policy:
route-policy policy1 statement 1 …. end-policy
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BGP Policy
• Introduction to RPL • BGP Bestpath • Influencing the Bestpath • Some Applications • RPL syntax
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Fra Baidu bibliotek
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If-then, Elseif
An if statement uses a conditional expression to decide which actions or dispositions should be taken for the given route.
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Nested If
The statements within an if statement may themselves be if statements:
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Parameterized Policy
• A hierarchical policy that passes values.
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Boolean Expressions
•Boolean expressions evaluate as either true or false. •RPL provides means to build compound conditions from simple conditions by means of Boolean operators. •There are three Boolean operators : negation (not), conjunction (and), and disjunction (or).
• Modularity
Exploit modularity configuration. to reuse common portions of
• Parameterization
For elements which are not exact copies of each other we can add parameterization ( think variables ) to get further reuse.
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Why RPL?
• Scaling
Using route-maps could lead to 100k – 1M lines of configuration (e.g. 1000s of BGP peers).
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Editing a route-policy
• Route-policy defines are atomic & non-incremental. • Invoke your favorite editor to do incremental changes:
edit route-policy policy1 [emacs | vim]
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What is RPL?
• Route Policy Language (RPL) • The Routing Policy Language (RPL) was developed to support large scale routing configurations.