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Cisco Bug: CSCut06312 - ePDG sends ICMP Fragmentation needed packet to its own Loopback.

Last Modified

May 21, 2018

Products (1)

  • Cisco ASR 5000 Series

Known Affected Releases


Description (partial)

When a UE attempts to retrieve a Visual Voicemail from the Visual Voicemail Server, a TCP socket is setup with a TCP MSS size of 1388.  When the Visual Voicemail Server sends the Visual Voicemail to the UE by the time the packet hits the SWU interface and the IP SEC headers are added the packet is over 1500 bytes which is the MTU of the SWU interface.  This causes the ePDG to send an ICMP Fragmentation Needed packet but it uses the SWU Loopback interface IP as the Source and Destination IP address.  This means the ICMP packet will never be returned to the Visual Voicemail Server to then resend the packet with a lower packet size.

IP Sec Tunnel between the UE and ePDG with an MTU size of 1500 bytes.  UE using a TCP MSS size of 1388 or higher when establishing a TCP socket.
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