A comparison of BGP as iGP with next-hop-self in a fully connected mesh vs BGP as iGP with next-hop-self with two Route Reflectors.
This is an effort to figure out the best of the two setups in terms of configuration and maintenance cost and it is inspired by a quest in the AWMN mailing list to find the best setup for AWMN nodes with many routers .
( AWMN is a wireless BGP internet where each wireless node has an Autonomous System Number and 1 to 15 routers with wireless interfaces. The routing within each node is done with static Routes or some iGP --usually OSPF-- or iBGP with next-hop-self. )
I assume that:
The maintenance cost is equal to the number of iBGP sessions --the number of connections in the mesh.
The total configuration cost is equal to the number of (neighbor) configuration stanzas for all iBGP connections.
The cost of adding a router is equal to the number of (neighbor) iBGP configuration stanzas needed in all the nodes in the mesh.
Get a little program that prints tables of maintenance and configuration costs for both setups.
$ wget https://raw.githubusercontent.com/ipduh/fmvsrr/master/fmvsrr.pl && chmod 755 fmvsrr.pl
Print costs for 2 to 27 routers.
$ ./fmvsrr.pl 27 N = Number of routers Πfm = Maintenance Cost in a Fully Connected Mesh Πrr = Maintenance Cost in a Two Route Reflectors Setup Kfm = Total Configuration Cost in a Fully Connected Mesh Krr = Total Configuration Cost in a Two Route Reflectors Setup Nfm = Cost of adding one router in a Fully Connected Mesh Nrr = Cost of adding one router in a Two Route Reflectors Setup N=2 Πfm=2 Πrr=2+ Kfm=2 Krr=2+ Nfm=2 Nrr=2+ N=3 Πfm=3 Πrr=3+ Kfm=6 Krr=3+ Nfm=6 Nrr=3 Ν=4 Πfm=6 Πrr=6 Kfm=12 Krr=9 Nfm=6 Nrr=3 Ν=5 Πfm=10 Πrr=7 Kfm=20 Krr=11 Nfm=8 Nrr=3 Ν=6 Πfm=15 Πrr=8 Kfm=30 Krr=13 Nfm=10 Nrr=3 Ν=7 Πfm=21 Πrr=9 Kfm=42 Krr=15 Nfm=12 Nrr=3 Ν=8 Πfm=28 Πrr=10 Kfm=56 Krr=17 Nfm=14 Nrr=3 Ν=9 Πfm=36 Πrr=11 Kfm=72 Krr=19 Nfm=16 Nrr=3 Ν=10 Πfm=45 Πrr=12 Kfm=90 Krr=21 Nfm=18 Nrr=3 Ν=11 Πfm=55 Πrr=13 Kfm=110 Krr=23 Nfm=20 Nrr=3 Ν=12 Πfm=66 Πrr=14 Kfm=132 Krr=25 Nfm=22 Nrr=3 Ν=13 Πfm=78 Πrr=15 Kfm=156 Krr=27 Nfm=24 Nrr=3 Ν=14 Πfm=91 Πrr=16 Kfm=182 Krr=29 Nfm=26 Nrr=3 Ν=15 Πfm=105 Πrr=17 Kfm=210 Krr=31 Nfm=28 Nrr=3 Ν=16 Πfm=120 Πrr=18 Kfm=240 Krr=33 Nfm=30 Nrr=3 Ν=17 Πfm=136 Πrr=19 Kfm=272 Krr=35 Nfm=32 Nrr=3 Ν=18 Πfm=153 Πrr=20 Kfm=306 Krr=37 Nfm=34 Nrr=3 Ν=19 Πfm=171 Πrr=21 Kfm=342 Krr=39 Nfm=36 Nrr=3 Ν=20 Πfm=190 Πrr=22 Kfm=380 Krr=41 Nfm=38 Nrr=3 Ν=21 Πfm=210 Πrr=23 Kfm=420 Krr=43 Nfm=40 Nrr=3 Ν=22 Πfm=231 Πrr=24 Kfm=462 Krr=45 Nfm=42 Nrr=3 Ν=23 Πfm=253 Πrr=25 Kfm=506 Krr=47 Nfm=44 Nrr=3 Ν=24 Πfm=276 Πrr=26 Kfm=552 Krr=49 Nfm=46 Nrr=3 Ν=25 Πfm=300 Πrr=27 Kfm=600 Krr=51 Nfm=48 Nrr=3 Ν=26 Πfm=325 Πrr=28 Kfm=650 Krr=53 Nfm=50 Nrr=3 Ν=27 Πfm=351 Πrr=29 Kfm=702 Krr=55 Nfm=52 Nrr=3
When the full mesh topology is used in a node with 10 routers the configuration and maintenance cost is ~4.5 times larger from a two-route-reflectors setup and the 11th router would cost me ~20 configuration stanzas and logging in 11 routers instead of ~3 stanzas in three routers ...
Full Mesh vs Route Reflectors
