The document outlines a troubleshooting methodology for VoIP issues, focusing on isolating problems and verifying causes related to connectivity and registration. It emphasizes the importance of DHCP server configuration, including options for central and local servers, and offers design tips to avoid common configuration mistakes. Key issues such as missing DHCP servers in voice VLANs and helper address configurations are highlighted as critical areas for resolution.

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