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VoiceCon Troubleshooting Tutorial
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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 …

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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Transcript

  • 1. VoIP Troubleshooting, Monitoring, and Metrics
      • Terry Slattery Principal Consultant CCIE #1026
  • 2. Troubleshooting Methodology (cont)
    • Isolate the origin of the problem
      • Collect problem data (description, scope, etc)‏
      • Narrow the list of causes
      • Collect additional data to validate or disprove causes
      • Create and test hypothesis
      • Repeat until problem is found and corrected
    • Narrow causes based on how VoIP works
      • Connectivity & Registration
      • Call Setup
      • Call Operation
      • Other Services
    Connectivity and Registration Call Setup Call Operation Misc Operation and Services
  • 3. Connectivity – DHCP
    • IP address assignment, default gateway, addl boot info - Cisco: option 150, Avaya: option 176
    • Local vs Central DHCP server
      • Short lease vs Long lease
      • Administrative overhead
      • Tracking address utilization
    Remote Branch Central Site DHCP Request DHCP DHCP
  • 4. Connectivity – DHCP Location Tradeoffs
    • Central
      • Multi-day address lease – longer than typical downtime
      • Reduces network equipment configuration
      • Good if many small branches exist
      • Handling long connectivity downtime due to disaster
    • Local
      • Short address lease
      • Manage DHCP config at each site
      • More appropriate at larger remote sites.
      • Good if downtime is more extensive
      • Very remote offices with poor connection reliability
  • 5. Local DHCP
    • Administered on each router
      • A good NCCM product can help here‏
    • Problem: no DHCP server in voice VLAN
        • ip dhcp pool VOICE
        • network 10.9.28.0 255.255.255.0
        • option 150 ip 10.9.14.4 10.9.20.2
        • default-router 10.9.28.1
        • dns-server 10.9.12.4 10.9.20.11
        • domain-name your-domain.com
    Remote Branch Central Site DHCP Request TFTP DHCP 10.9.14.4 10.9.28.1
  • 6. Central DHCP
    • Central server
      • Redundant servers are common
      • Commercial products: Bluecat and Infoblox
    • Problem: phones don't get a DHCP address
      • Helper address forwards DHCP requests
      • ip helper-address 10.9.14.4
    Remote Branch Central Site DHCP Request DHCP ip helper-address 10.9.14.4
  • 7. Connectivity - DHCP
    • Design tip: Separate address space for VoIP!!!
    • Avoid ACL entries for each voice vlan
      • Access lists for classification
      • Access lists for separation of voice & data
      • Design for summarization (simpler ACLs)‏
        • ip access-list extended Voice-to-Voice
        • permit udp 10.9.0.0 0.0.255.255 range 16384 32767 10.9.0.0 0.0.255.255 range 16384 32767
    • Good security practice: firewall between voice and data subnets
  • 8. DHCP Summary
    • Problems primarily from configuration mistakes
    • No DHCP server in voice VLAN
    • Central DHCP server reachability
      • Missing or incorrect helper address “ ip helper-address <addr> ”
    Remote Branch Central Site DHCP Request DHCP DHCP