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BGP
119
ixp
Must be EBGP, and sets default of no-fib and not add-own-as. Routes from this peer are
marked as IXP routes which affects filtering on route announcements
18.2.5. Route filtering
Each peer has a set of import and export rules which are applied to routes that are imported or exported from
the peer. There are also named bgp-filter which can be used as import-filters or export-filters.
The objects import and export work in exactly the same way, checking the routes imported or exported against a
set of rules and then possibly making changes to the attributes of the routes or even choosing to discard the route.
Each of these objects contain:-
• Cosmetic attributes such as name, comment, and source.
• Route matching attributes allowing specific routes to be selected
• Action attributes defining changes to the route
• A continuation attribute stop defining if the matching stops at this rule (default) or continues to check further
rules
The rules are considered in order. The first rule to match all of the matching attributes is used. If no rules match
then the default actions from the import/export object are used.
In addition, the top level import/export has a prefix list. If present then this will limit the prefixes processed at
a top level, dropping any that do not match the list without even considering the rules.
18.2.5.1. Matching attributes
The actual attributes are listed in the XML/XSD documentation for the software version. The main ones are:-
• A list of prefixes filters defining which prefixes to match
• There will be community tag checking and AS path checking in future
You can have a rule with no matching attribute which will always be applied, but this is generally pointless as no
later rules will be considered. If you want to define defaults then set them in the top level import/export object.
18.2.5.2. Action attributes
The actual attributes are listed in the XML/XSD documentation for the software version. The main ones are:-
• Adding specific community tags
• Removing specific community tags, including defaults added by the peer type.
• Dropping the route completely
• Changing the MED
• Changing the localpref
The logic works by creating a set of actions that are applied, and these are based on top level settings in the
peer (such as set-med) followed by the list of import or export named filters from which one matching action
is picked, and then followed by the peers indivdiual import and export rules from which one mathcing action
is picked. The matching action causes each of the settings that are present to replace what is currently picked.
E.g. if a MED is set in the top level and a named rule set the named rules set replaces the top level setting.
Important note - adding or removing community tags does not compound. For each setting (e.g. tag, untag,
med and localpref and any added in future) the latest that was found after checking top level peer settings, the
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