BGP常見問題解答之一
Q. What is the order of preference of attributes when some or all are applied to one neighbor in BGP?
A. The order of preference varies depending on whether the attributes are applied for inbound updates
or outbound updates.
For inbound updates the order of preference is:
route?map 1.
filter?list 2.
prefix?list, distribute?list 3.
For outbound updates the order of preference is:
prefix?list, distribute?list 1.
filter?list 2.
route?map 3.
Note: The attributes prefix?list and distribute?list are mutually exclusive, and only one command
(neighbor prefix?list or neighbor distribute?list) can be applied to each inbound or outbound
direction for a particular neighbor.
Cisco ? BGP: Frequently Asked Questions
Q. What does a next hop of 0.0.0.0 mean in show ip bgp output?
A. A network in the BGP table with a next hop address of 0.0.0.0 means that the network is locally
originated via redistribution of Interior Gateway Protocol (IGP) into BGP, or via a network or
aggregate command in the BGP configuration.
Q. What are the well known communities of the BGP community attribute?
A. The community attribute is a transitive, optional attribute designed to group destinations in a
certain community and apply certain policies (such as accept, prefer, or redistribute). The following
table shows the well known BGP communities.
Community Description
Local?AS Use in confederation scenarios to prevent sending
packets outside the local autonomous system (AS).
no?export Do not advertise to external BGP (eBGP) peers. Keep
this route within an AS.
no?advertise Do not advertise this route to any peer, internal or
external.
none Apply no community attribute when you want to clear
the communities associated with a route.
internet Advertise this route to the internet community, and any
router that belongs to it.
For more information on configuring communities, refer to the Configuring BGP Community
Filtering section in Configuring BGP.
Q. What formats can I use to configure the BGP community attribute?
A. In Cisco IOS
