03-14-2022 12:23 AM - edited 03-31-2022 11:15 PM
Some providers may advertise a specific route from within the summary route, along with this summary route. Why the provider may choose to advertise in this manner?
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03-14-2022 02:20 AM
Routing will always prefer the longest prefix match, so fo example if an organization has a /24 prefix they want to make reachable over two peering links, then they would advertize that prefix to both peers, but they could also advertize a /25 covering the lower half of their address range only towards Peer-A if (for some made up reason) they wanted inbound traffic to that sub-set of their address-range to prefer that link to Peer-A................if the link to Peer-A failed then all traffic to the /24 range would use the remaining available link as it is still advertizing the full /24 range.
03-14-2022 12:49 AM
As per i know when you like to do Traffic Engineering over different Router, may require leaking some routes, so it can be done based on the TE. The advertisement of a subset of more specific routes in addition to performing the summary. Leaking routes can be done at the process by explicitly stating the prefixes to suppress, or on a neighbor level by indicating which prefixes should not be suppressed.
03-14-2022 02:20 AM
Routing will always prefer the longest prefix match, so fo example if an organization has a /24 prefix they want to make reachable over two peering links, then they would advertize that prefix to both peers, but they could also advertize a /25 covering the lower half of their address range only towards Peer-A if (for some made up reason) they wanted inbound traffic to that sub-set of their address-range to prefer that link to Peer-A................if the link to Peer-A failed then all traffic to the /24 range would use the remaining available link as it is still advertizing the full /24 range.
03-14-2022 10:03 AM
Generally for the reason, and example, @JimWicks describes.
I.e. for some reason, you want to route a subnet prefix of summarized prefix differently.
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