Okay, confusion confirmed, although I can't rule out the confusion being in my head ![:D]( "Very Happy")
I don't understand what this has to do with ADD PATH.
The OP (like me) wants to have the defaults received from two BGP peers automatically result in ECMP routing. This is what's happening in all the other vendor gear I use (Cisco, Juniper, Bird on Linux, Dell OS10, etc), without configuring ADD PATH.
I think you're saying that there's a workaround: just have dedicated BGP instances for each peer, each of the defaults will look like the best path within that instance and get installed. Great. But that's not ECMP. There's nothing looking at the route costs to determine that they're equal. Every route from every peer is deemed equal, so as soon as you're talking about anything other than defaults, it falls down.
The way I'd expect ECMP to work without ADD PATH is that if you get far enough in the BGP route selection algorithm (basically at the point where you're comparing router IDs) both/all of the routes get inserted in the FIB (the main routing table in the non-ASIC case). That's what everyone else is doing. It doesn't have to change any BGP messages, at all, so I don't understand this functionality being gated behind ADD PATH. A single best path is still selected and advertised to peers. It's just that if there are routes with the same cost as the best path, they get inserted as well. That's it!
I don't understand what this has to do with ADD PATH.The OP (like me) wants to have the defaults received from two BGP peers automatically result in ECMP routing. This is what's happening in all the other vendor gear I use (Cisco, Juniper, Bird on Linux, Dell OS10, etc), without configuring ADD PATH.
I think you're saying that there's a workaround: just have dedicated BGP instances for each peer, each of the defaults will look like the best path within that instance and get installed. Great. But that's not ECMP. There's nothing looking at the route costs to determine that they're equal. Every route from every peer is deemed equal, so as soon as you're talking about anything other than defaults, it falls down.
The way I'd expect ECMP to work without ADD PATH is that if you get far enough in the BGP route selection algorithm (basically at the point where you're comparing router IDs) both/all of the routes get inserted in the FIB (the main routing table in the non-ASIC case). That's what everyone else is doing. It doesn't have to change any BGP messages, at all, so I don't understand this functionality being gated behind ADD PATH. A single best path is still selected and advertised to peers. It's just that if there are routes with the same cost as the best path, they get inserted as well. That's it!
Statistics: Posted by markonen — Wed Apr 03, 2024 6:22 pm