Description | This article describes the workaround for the issue on ForitGate when seeing 'Incorrect leftmost AS number' in BGP debugs |
Scope | FortiGate, FortiOS. |
Solution |
This issue will normally be seen when the BGP peering is not establishing.
Enable BGP debugs:
# diagnose ip router bgp all enable diagnose ip router bgp level info diagnose debug enable
The following would show up in debugs:
BGP: 10.10.10.2-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (4005), msg_size (86)
Check on the BGP peer as to why FortiGate is receiving 'incorrect AS number' error.
On FortiGate, a workaround would be to disable the command:
When this setting is enabled, BGP does a comparison between remote AS number of BGP peer configured locally with first AS in the path of received routes. Simply disabling this would resolve the issue. |
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