Created on 03-17-2024 09:34 AM Edited on 08-18-2024 12:19 AM By Jean-Philippe_P
Description | This article describes how to modify route preference using Local-Preference Attribute in BGP. |
Scope | FortiOS. |
Solution |
Local Peer: 10.9.26.94 configurations: On this FortiGate, there are two BGP peers: 10.9.17.42 and 10.9.26.163.
get router info bgp summary VRF 0 BGP router identifier 10.9.26.94, local AS number 65005 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 10.9.17.42 4 65005 10 9 2 0 0 00:00:42 1 10.9.26.163 4 65005 28 24 2 0 0 00:00:42 1 Total number of neighbors 2
Note that in the example below, the local peer (10.9.26.94) is receiving 10.10.10.0/24 from both the peers.
get router info bgp network VRF 0 BGP table version is 3, local router ID is 10.9.26.94 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 *>i10.10.10.0/24 10.9.17.42 0 100 0 0 i <-/1> * i 10.9.26.163 0 100 0 0 i <-/->
Total number of prefixes 1
This shows that the best route is installed in the routing-table via peer 10.9.17.42.
Suppose the goal is for 10.9.26.163 to have the preference over other peers, and it is necessary to to configure this preference parameter on the 10.9.26.163 itself. To do this, use the local-preference attribute. When the local peer (10.9.26.94) learns the routes, it also learns the value of local-preference and then installs the routing-table accordingly.
Remote peer: 10.9.26.163 configurations.
First, it is necessary to configure the prefix-list to match all (or specific prefix if required) IPs. After, configure Route-Map to refer to the prefix-list and configure a local-preference of 200 (which is higher than the default value of 100). Finally, use this route-map in route-map-out in the BGP configs for the peer 10.9.26.94.
config router prefix-list <- Configuring prefix-list. edit "prefix-list" config rule edit 1 set prefix 10.10.10.0 255.255.255.0 unset ge unset le next end next end
config router route-map <- Configuring route-map. edit "route-map-pref-200" config rule edit 1 set match-ip-address "prefix-list" <- Referring to prefix-list to match the IP(s). set set-local-preference 200 <- Allocating the preference. next end next end
config router bgp set as 65005 set router-id 10.9.26.163 config neighbor edit "10.9.26.94" set capability-graceful-restart enable set soft-reconfiguration enable set remote-as 65005 set route-map-out "route-map-pref-200" <- Referred route-map-out for advertised networks (10.10.10.0/24). next end
Now, upon resetting or soft resetting the BGP on the local peer (10.9.26.94).
execute router clear bgp ip 10.9.26.94 soft out
The newly installed BGP routes will have 10.9.26.163 as the best route because of the higher local-preference.
get router info bgp network VRF 0 BGP table version is 1, local router ID is 10.9.26.94 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 * i10.10.10.0/24 10.9.17.42 0 100 0 0 i <-/-> *>i 10.9.26.163 0 200 0 0 i <-/1>
Total number of prefixes 1 |
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