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In the network topology shown below, two spokes are connected to a hub using iBGP:
Spoke-1 is advertising 20.20.20.1/24 to the HUB:
SPK_1 # get router info bgp neighbors 10.10.1.1 advertised-routes
VRF 0 BGP table version is 6, local router ID is 192.168.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight RouteTag Path
*>i20.20.20.0/24 10.10.1.3 100 32768 0 i <-/->
Total number of prefixes 1
On the hub, the route is received from Spoke-1 and then advertised to Spoke-2:
HUB # get router info bgp neighbors 10.10.1.3 received-routes
VRF 0 BGP table version is 16, local router ID is 10.212.134.201
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight RouteTag Path
*>i20.20.20.0/24 10.10.1.3 100 0 0 i <-/->
Total number of prefixes 1
HUB # get router info bgp neighbors 10.10.1.2 advertised-routes
VRF 0 BGP table version is 16, local router ID is 10.212.134.201
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight RouteTag Path
*>i20.20.20.0/24 10.10.1.3 100 0 0 i <-/->
Total number of prefixes 1
On Spoke-2, the route is received from the HUB but is not being installed in the BGP Table:
SPK_2 # get router info bgp neighbors 10.10.1.1 received-routes
VRF 0 BGP table version is 5, local router ID is 192.168.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight RouteTag Path
*>i1.1.1.1/32 10.10.1.1 100 0 0 i <0/0>
*>i10.100.0.0/18 10.10.1.1 100 0 0 i <0/0>
*>i20.20.20.0/24 10.10.1.3 100 0 0 i <0/0>
Total number of prefixes 3
Note: If soft reconfiguration is not enabled, received-routes will show no results. This is expected, see this article: Technical Tip : BGP Routing process when 'Soft Reconfiguration' is enabled.
SPK_2 # get router info bgp neighbors 10.10.1.1 received-routes
% Inbound soft reconfiguration not enabled
% No prefix for neighbor 10.10.1.1
The 20.20.20.1/24 network is not present in the BGP table:
SPK_2 # get router info bgp network
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
VRF 0 BGP table version is 5, local router ID is 192.168.1.1
Network Next Hop Metric LocPrf Weight RouteTag Path
*>i1.1.1.1/32 10.10.1.1 0 100 0 0 i <0/1>
*>i10.100.0.0/18 10.10.1.1 0 100 0 0 i <0/1>
*> 10.176.0.0/18 0.0.0.0 100 32768 0 i <0/1>
Total number of prefixes 3
Diagnostics:
Enable BGP debug messages on Spoke-2:
diagnose ip router bgp all enable
diagnose ip router bgp level info
diagnose debug enable
Trigger a route refresh of inbound routes on Spoke-2:
execute router clear bgp ip 10.10.1.1 soft in
Debug output:
[root] BGP: [RIB] Scanning BGP Network Routes for VRF 0...
[root] BGP: 10.10.1.1-Outgoing [DECODE] Msg-Hdr: type 2, length 53
[root] BGP: 10.10.1.1-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (34), msg_size (34)
[root] BGP: 10.10.1.1-Outgoing [DECODE] Update: NLRI Len(9)
[root] BGP: 10.10.1.1-Outgoing [FSM] State: Established Event: 27
[root] BGP: 10.10.1.1-Outgoing [RIB] Update: Received Prefix 1.1.1.1/32 path_id 0
[root] BGP: [DAMP] bgp_rfd_rt_update(): Route State: NONE, ret=0
[root] BGP: 10.10.1.1-Outgoing [RIB] Update: ...duplicate route ignored
[root] BGP: 10.10.1.1-Outgoing [RIB] Update: Received Prefix 10.100.0.0/18 path_id 0
[root] BGP: [DAMP] bgp_rfd_rt_update(): Route State: NONE, ret=0
[root] BGP: 10.10.1.1-Outgoing [RIB] Update: ...duplicate route ignored
[root] BGP: 10.10.1.1-Outgoing [DECODE] Msg-Hdr: type 2, length 62
[root] BGP: 10.10.1.1-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (43), msg_size (43)
[root] BGP: 10.10.1.1-Outgoing [DECODE] Update: NLRI Len(4)
[root] BGP: 10.10.1.1-Outgoing [FSM] State: Established Event: 27
[root] BGP: 10.10.1.1-Outgoing [RIB] Update: Prefix 20.20.20.0/24 path_id 0 denied due to originator is us
[root] BGP: bgp_ipc_server_accept:670 create ipc_handler=0x7fb004efb0c0 for sock=29
To disable BGP debug messages:
diagnose ip router bgp all disable
diagnose ip router bgp level none
diagnose debug reset
The issue occurs because Spoke-1 and Spoke-2 are configured with the same router ID. To resolve the issue, change the router ID on either spoke to a unique value. Note that if no router-id is configured, FortiOS will use the assigned IP address of an existing interface. If spoke devices use the same IP addresses for local interfaces, this issue will be encountered with higher frequency.
Warning: Changing router-id restarts all BGP neighborships on the affected spoke and may cause network disruption for affected BGP networks while the peers re-establish.
config router bgp
set router-id x.x.x.x <----- Replace x.x.x.x with the IP address that will be used as the router ID.
end
Related articles:
Troubleshooting Tip: Troubleshooting BGP over IPsec
Technical Tip: FortiOS BGP Resource List
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