Technical Tip: Difference between BGP neighbor/Route map weight parameter

[hgarara]

Description	This article describes the difference between 'set weight' under BGP neighbor, and 'set set-weight' under BGP route-map.
Scope	FortiGate.
Solution	Using the weight parameter under the route map gives the granular control over each route from/through a neighbor. To better understand, consider the below-given topology and scenario(s): HUB: (tunnel ip 10.10.1.1, 10.10.2.1) 6.6.6.0/24 spoke1: (tunnel ip 10.10.1.2, 10.10.2.2 3.3.3.0/24 4.4.4.0/24 3.3.4.0/24 spoke2: (tunnel ip 10.10.1.3, 10.10.2.3) 1.1.1.0/24 2.2.2.0/24 1.1.2.0/24 1.1.3.0/24 The routing table of HUB before making any changes: HUB # get router info bgp network    Network          Next Hop            Metric     LocPrf Weight RouteTag Path * i1.1.1.0/24       10.10.2.3       0             100      0        0 i <-/-> *>i                 10.10.1.3       0             100      0        0 i <-/1> *>i1.1.2.0/24       10.10.1.3       0             100      0        0 i <-/1> * i                 10.10.2.3       0             100      0        0 i <-/-> * i1.1.3.0/24       10.10.2.3       0             100      0        0 i <-/-> *>i                 10.10.1.3       0             100      0        0 i <-/1> * i2.2.2.0/24       10.10.2.3       0             100      0        0 i <-/-> *>i                 10.10.1.3       0             100      0        0 i <-/1> * i3.3.3.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> * i3.3.4.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> * i4.4.4.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> *> 6.6.6.0/24       0.0.0.0                       100  32768        0 i <-/1> Total number of prefixes 8 Scenario 1 (BGP neighbor): Initially based on the BGP route selection process, 10.10.1.3 neighbor’s route will be selected over 10.10.2.3. Once increasing the 'BGP neighbor' weight of neighbor 10.10.2.3, this will eventually prioritize all routes of 10.10.2.3 over 10.10.1.3. config router bgp     config neighbor         edit "10.10.2.3"             set advertisement-interval 1             set capability-graceful-restart enable             set link-down-failover enable             set soft-reconfiguration enable             set remote-as 65400             set route-map-in "block-map"             set route-reflector-client enable         next end (exe router clear bgp all soft) --> soft reset BGP. Results: HUB# get router info bgp network    Network          Next Hop            Metric     LocPrf Weight RouteTag Path *>i1.1.1.0/24       10.10.2.3       0             100  32770        0 i <-/1> * i                 10.10.1.3       0             100      0        0 i <-/-> * i1.1.2.0/24       10.10.1.3       0             100      0        0 i <-/-> *>i                 10.10.2.3       0             100  32770        0 i <-/1> *>i1.1.3.0/24       10.10.2.3       0             100  32770        0 i <-/1> * i                 10.10.1.3       0             100      0        0 i <-/-> *>i2.2.2.0/24       10.10.2.3       0             100  32770        0 i <-/1> * i                 10.10.1.3       0             100      0        0 i <-/-> * i3.3.3.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> * i3.3.4.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> * i4.4.4.0/24       10.10.2.2       0             100      0        0 i <-/-> *>i                 10.10.1.2       0             100      0        0 i <-/1> *> 6.6.6.0/24       0.0.0.0                       100  32768        0 i <-/1> Total number of prefixes 8 HUB# get router info routing-table bgp Routing table for VRF=0 B       1.1.1.0/24 [200/0] via 10.10.2.3 (recursive is directly connected, HUBWAN2), 00:00:41, [1/0] B       1.1.2.0/24 [200/0] via 10.10.2.3 (recursive is directly connected, HUBWAN2), 00:00:41, [1/0] B       1.1.3.0/24 [200/0] via 10.10.2.3 (recursive is directly connected, HUBWAN2), 00:00:41, [1/0] B       2.2.2.0/24 [200/0] via 10.10.2.3 (recursive is directly connected, HUBWAN2), 00:00:41, [1/0] B       3.3.3.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:27:06, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:27:06, [1/0] B       3.3.4.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:27:06, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:27:06, [1/0] B       4.4.4.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:27:06, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:27:06, [1/0] Scenario 2 (BGP route-map): Block 1.0.0.0/24 (i.e 1.1.1.0/24, 1.1.3.0/24) subnet from neighbor 10.10.2.3, however allow 1.1.2.0/24 using higher weight under route map (1.1.2.0/24 should not be routed anymore through 10.10.1.3). config router access-list     edit "1.0.0.0/8"         config rule             edit 1                 set prefix 1.0.0.0 255.0.0.0             next             edit "1.1.2.0/24"         config rule             edit 1                 set prefix 1.1.2.0 255.255.255.0             next     end HUB# config router route-map HUB(route-map) # edit "block-map" HUB(block-map) # show config router route-map     edit "block-map"         config rule             edit 1                 set match-ip-address "1.1.2.0/24"                 set set-weight 32780             next             edit 2                 set action deny                 set match-ip-address "1.0.0.0/8"             next         end     end (exe router clear bgp all soft) --> Soft reset bgp. Results: HUB# get router info bgp network VRF 0 BGP table version is 10, local router ID is 6.6.6.6 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,               S Stale Origin codes: i - IGP, e - EGP, ? - incomplete    Network          Next Hop            Metric     LocPrf Weight RouteTag Path *>i1.1.1.0/24       10.10.1.3       0             100      0        0 i <-/1> *>i1.1.2.0/24       10.10.2.3       0             100  32780        0 i <-/1> * i                 10.10.1.3       0             100      0        0 i <-/-> *>i1.1.3.0/24       10.10.1.3       0             100      0        0 i <-/1> *>i2.2.2.0/24       10.10.1.3       0             100      0        0 i <-/1> *>i3.3.3.0/24       10.10.1.2       0             100      0        0 i <-/1> * i                 10.10.2.2       0             100      0        0 i <-/-> *>i3.3.4.0/24       10.10.1.2       0             100      0        0 i <-/1> * i                 10.10.2.2       0             100      0        0 i <-/-> *>i4.4.4.0/24       10.10.1.2       0             100      0        0 i <-/1> * i                 10.10.2.2       0             100      0        0 i <-/-> *> 6.6.6.0/24       0.0.0.0                       100  32768        0 i <-/1> Total number of prefixes 8 HUB# get router info routing-table bgp Routing table for VRF=0 B       1.1.1.0/24 [200/0] via 10.10.1.3 (recursive is directly connected, HUB), 00:00:34, [1/0] B       1.1.2.0/24 [200/0] via 10.10.2.3 (recursive is directly connected, HUBWAN2), 00:00:34, [1/0] B       1.1.3.0/24 [200/0] via 10.10.1.3 (recursive is directly connected, HUB), 00:00:34, [1/0] B       2.2.2.0/24 [200/0] via 10.10.1.3 (recursive is directly connected, HUB), 00:09:17, [1/0] B       3.3.3.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:16:21, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:16:21, [1/0] B       3.3.4.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:16:21, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:16:21, [1/0] B       4.4.4.0/24 [200/0] via 10.10.1.2 (recursive is directly connected, HUB), 00:16:21, [1/0]                    [200/0] via 10.10.2.2 (recursive is directly connected, HUBWAN2), 00:16:21, [1/0] Note: The above-mentioned scenario could differ based on a sequence of rules in route map. The rule ID will determine which rule will be matched first: Technical Tip: Order of Processing Route-map Rules. Related article:  Technical Tip: Use BGP Weight attribute to prefer default route received from neighbor over 'capabil...