Describes filtering BGP routes based on attributes to control route acceptance and advertisement.
BGP attribute filter is a feature that
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checks the integrity of BGP updates in BGP update messages
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optimizes reactions when detecting invalid attributes, and
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filters attributes received in the incoming update message.
Purpose and operation of the attribute filter
The BGP attribute filter feature checks the integrity of BGP updates in BGP update messages. It also optimizes reactions when it detects invalid attributes. BGP update messages contain a list of mandatory and optional attributes. These attributes include MED, LOCAL_PREF, and COMMUNITY, and so on. In some cases, if attributes are malformed, filtering them at the receiving router is necessary. The BGP attribute filter regulates which attributes are accepted in incoming update messages. The attribute filter can also filter any attributes that may potentially cause undesirable behavior on the receiving router.
Some BGP updates are malformed due to incorrect formatting of attributes, such as the Network Layer Reachability Information (NLRI) or other fields in the update message. These malformed updates, when received, cause undesirable behavior on the receiving routers. Such undesirable behavior may occur during update message parsing or during re-advertisement of received NLRIs. In such scenarios, it's better to filter these corrupted attributes at the receiving end.