Summary
This chapter introduced a basic systematic troubleshooting methodology. VPNs are particularly suited to end-to-end, bottom-up, or top-down troubleshooting.
For some VPN technologies, such as L2F, L2TP version 2, and PPTP, end-to-end troubleshooting is asymmetric, whereas for others, such as MPLS layer-3 VPNs and L2TP version 3, end-to-end troubleshooting is symmetric.
Preparatory steps, such as drawing network diagrams, recording software versions, and backing up device configurations, are recommended.
Finally, VPN troubleshooting tools, such as the show, ping, traceroute, and debug commands, were introduced. Usage guidelines for the debug command were also discussed.
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