VoiceCon Troubleshooting Tutorial


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Networking expert Terry Slattery of Chesapeake NetCraftsmen will present a tutorial on IP telephony troubleshooting and management at VoiceCon Orlando 2009. This excerpt shows Terry's explanation of troubleshooting DHCP-related problems in IPT.

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VoiceCon Troubleshooting Tutorial

  1. 1. VoIP Troubleshooting, Monitoring, and Metrics <ul><ul><li>Terry Slattery Principal Consultant CCIE #1026 </li></ul></ul>
  2. 2. Troubleshooting Methodology (cont) <ul><li>Isolate the origin of the problem </li></ul><ul><ul><li>Collect problem data (description, scope, etc)‏ </li></ul></ul><ul><ul><li>Narrow the list of causes </li></ul></ul><ul><ul><li>Collect additional data to validate or disprove causes </li></ul></ul><ul><ul><li>Create and test hypothesis </li></ul></ul><ul><ul><li>Repeat until problem is found and corrected </li></ul></ul><ul><li>Narrow causes based on how VoIP works </li></ul><ul><ul><li>Connectivity & Registration </li></ul></ul><ul><ul><li>Call Setup </li></ul></ul><ul><ul><li>Call Operation </li></ul></ul><ul><ul><li>Other Services </li></ul></ul>Connectivity and Registration Call Setup Call Operation Misc Operation and Services
  3. 3. Connectivity – DHCP <ul><li>IP address assignment, default gateway, addl boot info - Cisco: option 150, Avaya: option 176 </li></ul><ul><li>Local vs Central DHCP server </li></ul><ul><ul><li>Short lease vs Long lease </li></ul></ul><ul><ul><li>Administrative overhead </li></ul></ul><ul><ul><li>Tracking address utilization </li></ul></ul>Remote Branch Central Site DHCP Request DHCP DHCP
  4. 4. Connectivity – DHCP Location Tradeoffs <ul><li>Central </li></ul><ul><ul><li>Multi-day address lease – longer than typical downtime </li></ul></ul><ul><ul><li>Reduces network equipment configuration </li></ul></ul><ul><ul><li>Good if many small branches exist </li></ul></ul><ul><ul><li>Handling long connectivity downtime due to disaster </li></ul></ul><ul><li>Local </li></ul><ul><ul><li>Short address lease </li></ul></ul><ul><ul><li>Manage DHCP config at each site </li></ul></ul><ul><ul><li>More appropriate at larger remote sites. </li></ul></ul><ul><ul><li>Good if downtime is more extensive </li></ul></ul><ul><ul><li>Very remote offices with poor connection reliability </li></ul></ul>
  5. 5. Local DHCP <ul><li>Administered on each router </li></ul><ul><ul><li>A good NCCM product can help here‏ </li></ul></ul><ul><li>Problem: no DHCP server in voice VLAN </li></ul><ul><ul><ul><li>ip dhcp pool VOICE </li></ul></ul></ul><ul><ul><ul><li>network </li></ul></ul></ul><ul><ul><ul><li>option 150 ip </li></ul></ul></ul><ul><ul><ul><li>default-router </li></ul></ul></ul><ul><ul><ul><li>dns-server </li></ul></ul></ul><ul><ul><ul><li>domain-name your-domain.com </li></ul></ul></ul>Remote Branch Central Site DHCP Request TFTP DHCP
  6. 6. Central DHCP <ul><li>Central server </li></ul><ul><ul><li>Redundant servers are common </li></ul></ul><ul><ul><li>Commercial products: Bluecat and Infoblox </li></ul></ul><ul><li>Problem: phones don't get a DHCP address </li></ul><ul><ul><li>Helper address forwards DHCP requests </li></ul></ul><ul><ul><li>ip helper-address </li></ul></ul>Remote Branch Central Site DHCP Request DHCP ip helper-address
  7. 7. Connectivity - DHCP <ul><li>Design tip: Separate address space for VoIP!!! </li></ul><ul><li>Avoid ACL entries for each voice vlan </li></ul><ul><ul><li>Access lists for classification </li></ul></ul><ul><ul><li>Access lists for separation of voice & data </li></ul></ul><ul><ul><li>Design for summarization (simpler ACLs)‏ </li></ul></ul><ul><ul><ul><li>ip access-list extended Voice-to-Voice </li></ul></ul></ul><ul><ul><ul><li>permit udp range 16384 32767 range 16384 32767 </li></ul></ul></ul><ul><li>Good security practice: firewall between voice and data subnets </li></ul>
  8. 8. DHCP Summary <ul><li>Problems primarily from configuration mistakes </li></ul><ul><li>No DHCP server in voice VLAN </li></ul><ul><li>Central DHCP server reachability </li></ul><ul><ul><li>Missing or incorrect helper address “ ip helper-address <addr> ” </li></ul></ul>Remote Branch Central Site DHCP Request DHCP DHCP