Check the logs and adjust their settings if required

During normal operation, the log settings will show any problems on the network but may not provide the level of details required to fully troubleshoot the problem. The reason for this is that the level of detail required for troubleshooting would quickly overwhelm the daily logs without any real benefit.

GTP related events in the event log will have message IDs in the range 41216 to 41222. For more information on GTP log messages, see the Log Message Reference. For more information on logging in general, see the Logging and Reporting guide.

Once there is a problem to troubleshoot, check the logs to trace the traffic patterns and narrow down the possible sources of the problem. There may be enough detail for you to locate and fix the problem without changing the log settings.

Remember to set any changes you made to the log settings back to their original values when you are done troubleshooting. Otherwise, the amount of detail will overwhelm your logging.

However, if more detail is required you can change settings such as:

• Lower the Log Frequency number in GTP Profiles so fewer or no log messages are dropped. This will allow a more accurate picture of everything happening on the network, where you may have had only a partial picture before.
• Ensure all the GTP log events are enabled to provide you with a complete picture. l Ensure that all relevant event types are enabled under Log & Report > Log Config > Log Settings.

For more information on GTP related logging, see Logging events on the Carrier-enabled FortiGate unit.

General information to look for in the logs includes:

• Are all packets having problems or just certain types? l Are all devices on the network having problem, or just certain devices? l Is it just GTP traffic that is having problems or are all types of traffic having the same problem?

Check the routing table

On any network, the routing table determines how packets reach their destination. This is also true on a carrier network.

If the Carrier-enabled FortiGate unit is running in NAT mode, verify that all desired routes are in the routing table — local subnets, default routes, specific static routes, and dynamic routing protocols. For complete information, it is best to check the routing table in the CLI. This method provides more complete information.

To check the routing table using the CLI

# get router info routing-table all

Codes: K – kernel, C – connected, S – static, R – RIP, B – BGP

O – OSPF, IA – OSPF inter area

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2 E1 – OSPF external type 1, E2 – OSPF external type 2

i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, ia – IS-IS inter area * – candidate default

S* 0.0.0.0/0 [10/0] via 192.168.183.254, port2

S 1.0.0.0/8 [10/0] via 192.168.183.254, port2

S 2.0.0.0/8 [10/0] via 192.168.183.254, port2

C 10.142.0.0/23 is directly connected, port3

B 10.160.0.0/23 [20/0] via 10.142.0.74, port3, 2d18h02m C 192.168.182.0/23 is directly connected, port2

Examining an entry from the routing table above:

B 10.160.0.0/23 [20/0] via 10.142.0.74, port3, 2d18h02m

B	BGP. The routing protocol used.
10.160.0.0/23	The destination of this route including netmask.
[20/0]	20 indicates and administrative distance of 20 out of a range of 0 to 255. 0 is an additional metric associated with this route, such as in OSPF
10.142.0.74	The gateway, or next hop.
port3	The interface used by this route.
2d18h02m	How old this route is, in this case almost three days old.