Fragmentation needed

Forum|Forum|8 years ago
February 1, 2018
6 replies
10264 views

I have setup a new phone system in my work place and configure it to work over the VPN tunnel. everything working fine except video call.I have checked the port matrix for the phone system and all are allowed. when I tried to sniff the packets using the wire shark I received a message from the fortigate 1240B "destination unreachable (fragmentation needed)". Phone system MTU

## VIDEO_PAYLOAD_LENGTH specifies the video packets payload length (bytes)

## Valid values are 0, 1200 through 1460; where 0 means that the video packets payload length is calculated

## according to MTU_SIZE parameter. If MTU_SIZE is 1500 bytes then video payload length will be:

## 1460 == 1500 Bytes (Ethernet) - 20 (IP) - 8 (UDP) - 12 (RTP). In similar way if MTU_SIZE is 1496 bytes

## then video payload length will be: 1456.

## The default value is 0.

## This parameter is supported by:

## H1xx SIP R1.0 and later

## SET VIDEO_PAYLOAD_LENGTH 1460

even when i tried "set honor-df disable" the system does not recognize it as built-in command. Please advise me to resolve this issue.

Toshi_Esumi

SuperUser

Looks like your phone system has capability to adjust payload length manually. Have you tried the payload length like 1360, which should be well shorter than the MTU over the tunnel?

mtalaqAuthor

New Member

toshiesumi wrote:
Looks like your phone system has capability to adjust payload length manually. Have you tried the payload length like 1360, which should be well shorter than the MTU over the tunnel?

thanks for your replay.

there is no option to change the MTU size in the phone system