• Next HopNOTE: There are no hard coded limits on the number of attributes that are supported in the BGP.Taking into account other constraints such as the Packet Size, maximum number of attributes aresupported in BGP.CommunitiesBGP communities are sets of routes with one or more common attributes. Communities are a way toassign common attributes to multiple routes at the same time.NOTE: Duplicate communities are not rejected.Best Path Selection CriteriaPaths for active routes are grouped in ascending order according to their neighboring external ASnumber (BGP best path selection is deterministic by default, which means the bgp non-deterministic-med command is NOT applied).The best path in each group is selected based on specific criteria. Only one “best path” is selected at atime. If any of the criteria results in more than one path, BGP moves on to the next option in the list. Forexample, two paths may have the same weights, but different local preferences. BGP sees that the Weightcriteria results in two potential “best paths” and moves to local preference to reduce the options. If anumber of best paths is determined, this selection criteria is applied to group’s best to determine theultimate best path.In non-deterministic mode (the bgp non-deterministic-med command is applied), paths arecompared in the order in which they arrive. This method can lead to Dell Networking OS choosingdifferent best paths from a set of paths, depending on the order in which they were received from theneighbors because MED may or may not get compared between the adjacent paths. In deterministicmode, Dell Networking OS compares MED between the adjacent paths within an AS group because allpaths in the AS group are from the same AS.NOTE: The bgp bestpath as-path multipath-relax command is disabled by default,preventing BGP from load-balancing a learned route across two or more eBGP peers. To enableload-balancing across different eBGP peers, enable the bgp bestpath as-path multipath-relax command. A system error results if you configure the bgp bestpath as-path ignorecommand and the bgp bestpath as-path multipath-relax command at the same time.Only enable one command at a time.The following illustration shows that the decisions BGP goes through to select the best path. The listfollowing the illustration details the path selection criteria.Border Gateway Protocol IPv4 (BGPv4) 171
