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Troubleshooting the BFD invalid TTL value log message

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TitleTroubleshooting the BFD invalid TTL value log message
Objective
This article explains how to find the source of the BFD packets which trigger the BFD invalid TTL value log or any other BFD related errors.
07/19/2004 18:56:24.25 <Warn:BFD.RxPktInv> Received BFD an invalid packet on VLAN <> Error:Invalid ttl value for single Hop session

 
Environment
Summit and Blackdiamond
Exos All
Procedure
Match the BFD packets using the following ACL and apply the ACL to the ingress VLAN or the port.
entry test {
if match all {
protocol udp;
destination-port 3784;
}
then {
mirror-cpu;
log;
}
} 

Configure access-list <policy name> vlan <vlan name> ingress or 

Configure access-list <policy name> port <port number> ingress
Add the kernel event so that the actual packet is logged in the memory-buffer.
For summit stand-alone: 
Configure log filter defaultfilter add events kern.info  or 

For Blackdiamond or summit stack:

Configure log filter defaultfilter add events kern.card.info  

Sample log: 

# show log
07/19/2004 18:33:08.48 <Info:Kern.Info> 10.125.242.125:49152 -> 10.125.242.126:3784 UDP v4 hLen: 20 ttl: 254 tos: 0xc0 tLen: 52
07/19/2004 18:33:08.48 <Info:Kern.Info> 00:04:96:98:ae:af -> 00:04:96:98:88:1b IP
07/19/2004 18:33:08.48 <Info:Kern.Info> 70-byte packet from 1:3 (vlanId=121) matches rule test
07/19/2004 18:33:08.44 <Warn:BFD.RxPktInv> Received BFD an invalid packet on VLAN DIR-0121 Error:Invalid ttl value for single Hop session
07/19/2004 18:33:07.48 <Info:Kern.Info> 10.125.242.125:49152 -> 10.125.242.126:3784 UDP v4 hLen: 20 ttl: 254 tos: 0xc0 tLen: 52
07/19/2004 18:33:07.48 <Info:Kern.Info> 00:04:96:98:ae:af -> 00:04:96:98:88:1b IP
07/19/2004 18:33:07.48 <Info:Kern.Info> 70-byte packet from 1:3 (vlanId=121) matches rule test

From the sample log above, you could identify the source of the BFD packet as 10.125.242.125.
 

Additional notes
Please be aware that this will mirror the matched traffic to the CPU for logging purposes and will log each iteration of the packets. So, use the above ACL and the configuration only for troubleshooting purposes. Refer the article below for more information about logging the packets in EXOS.
How to Capture received packets using an ACL and log the packet header to the "show log" output

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