1.5.e i Route reflector A route reflector is a BGP router that is allowed to ignore the iBGP loop avoidance rule and as such, is allowed to advertise updates received from an iBGP peer to another iBGP peer under specific conditions. The deployment of a route reflector can eliminate the BGP full-mesh requirement and greatly… read more »
1.5.f i Multipath, add-path BGP routers and route-reflectors propagate only their best path over their sessions. The advertisement of a prefix replaces the previous announcement of that prefix (known as an implicit withdraw). While this achieves better scaling, it comes at a cost of preventing path diversity. BGP additional path is a BGP extension that… read more »
1.5.d i local-as, allowas-in, remove-private-as Local AS Local AS configuration, essentially works the same way as the no-export community function, in that prefixes that are tagged are only advertised to neighbours within the same sub-AS, not to other sub-AS’ or eBGP peers. It allows a router to appear to be a member of a second… read more »
To decide which route is the best, each BGP router has a “best path selection” algorithm, where the information from two similar paths are compared. This is because it is not unusual for a BGP speaker to receive the same route from multiple peers. In fact, this is quite normal when you have multiple upstreams… read more »
BGP is an exterior gateway protocol, that is intended to be used between different autonomous systems. BGP is a path-vector protocol meaning it’s routes are composed of a list of AS’ on the path to any given destination. Routers running BGP are known as BGP ‘speakers’ and BGP neighbours are known as ‘peers’. If a… read more »
1.5.c i Attribute manipulation In BGP, there are two main options to manipulate the Weight attribute: per-neighbor basis per-prefix basis. Note: The BGP’s Weight Path attribute is the first path attribute BGP checks in the election of the best path in the BGP table on Cisco IOS Routers. BGP prefers the path for the entry… read more »