- Auto Anchor SSID between Wireless LAN Controllers acting as MC
- Enabling Central Web Authentication on ISE
- Configuring Auto Anchor and Mobility Groups on Wireless Services
- Configuring Wireless Multicast on Wireless LAN Controllers
- Converged Access Consolidated Quick Reference Templates for Wireless LAN
- Converged Access Controller AP Join Issue Troubleshoot with Traces
- Converged Access Controllers MAC Address Entry for Network Mobility Service Protocol
- Configuration Example: Converged Access Management through Prime Infrastructure with SNMP v2 and v3
- Converged Access Path Maximum Transmission Unit Discovery
- Third-Party Certificate Installation on Converged Access Wireless LAN Controllers
- Configuration Example: Converged Access for WLC EAP-FAST with Internal RADIUS Server
- Converged Access and WLC Local EAP Authentication Configuration Example
- Configuration Example: Custom Web Authentication with Local Authentication
- Dynamic VLAN Assignment with Converged Access and ACS 5.2 Configuration Example
- Configuration Example: External RADIUS Server EAP Authentication
- External Web Authentication on Converged Access
- Installing Wireless Services
- Local Web Authentication with External RADIUS Authentication
- Local Web Authentication on Converged Access
- PEAP Authentication with Microsoft NPS Configuration
- QoS on Converged Access Controllers and Lightweight Access Points
- Configuration Example: TACACS Administrator Access to Converged Access Wireless LAN Controllers
- Configuration Example: Unified Access WLC Guest Anchor with Converged Access
- VideoStream Troubleshooting
- Custom Web Authentication Locally Hosted on WLC or an External Server
- Wireless Converged Access Chromecast Configuration Example
- Web Passthrough Configuration Example
- Configuration Examples: WPA2-PSK and Open Authentication
Converged Access Path Maximum Transmission Unit Discovery
This document describes the Path Maximum Transmission Unit (MTU) Discovery algorithm for Wireless LAN Controller (WLC) (version 6.0 and above) and Converged Access.
- Supported Platforms and Releases
- Network Diagram
- Setting Maximum Transmission Unit
- Verifying Dynamic Path Maximum Transmission
- Troubleshooting Dynamic Path Maximum Transmission Unit
Supported Platforms and Releases
The information in this document is based on Cisco 5700 Series Wireless LAN Controller.
Network Diagram
Sender (Access Point) > (Multiprotocol Label Switching [MPLS] or Router) > Receiver (WLC or Converged Access)
Setting Maximum Transmission Unit
The sender detects the default MTU and sends a discovery request (Access Point [AP] to WLC). The request is for 1500 bytes with a Don't Fragment (DF) bit set. If the receiver receives the request, then it replies with a 1500 bytes packet. When the sender receives the reply from the receiver, the MTU path is set at 1500 MTU.
In cases, where the receiver does not receive the discovery request (or the sender does not receive the response from the receiver), the MTU is set to 576 and the dynamic discovery process starts.
Dynamic Path Maximum Transmission Unit Discovery
The sender or receiver if allowed, sets the MTU information available in the Internet Control Message Protocol (ICMP) as the next value for MTU.
If no information available, the sender or receiver receives an ICMP error. The initial MTU size is then set at 576 and dynamic discovery is in progress. Every 30 seconds, the sender attempts to increase the MTU to check for improvements in the path.
The sender can set the MTU values as 576, 1006, 1492, and 1500. Based on the router configuration, the customer can see the ICMP errors every 30 seconds for every AP.
ICMP Error over MPLS Example
MPLS: ICMP: dst (10.10.10.10) frag. needed and DF set unreachable sent to 192.0.2.5
Verifying Dynamic Path Maximum Transmission
To verify the Dynamic Path Maximum Transmission (PMTU), use the show ap config general command in EXEC mode.
Device(config)# show ap config general | b <APname> . CAPWAP Path MTU : 1500 Device> show ap config general <APname> . . CAPWAP Path MTU.................................. 1500
Troubleshooting Dynamic Path Maximum Transmission Unit
To troubleshoot Dynamic PMTU issues, perform a packet capture on the AP switch port.
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