One day customer report that they can not set MTU on Ethernet boards EFT4, EFT8, EFT8A more than 1535
NE SCC version 188.8.131.52
MTU parameter is invalid, Error code:39680
Customer need set MTU on this boards more than 1535 byte
MTU is the maximum packet length Ethernet interface can support pass through (including 4 Bytes CRC section).
Jumbo frame is the frame whose MTU is over 1535 Bytes, and the maximum is 9600 Bytes. Jumbo frame MTU is between 1536 ~ 9600 Bytes.
3.Jumbo Frame Type Field
Jumbo Frame type field is the 2 Bytes behind and closed to.SA (source MAC address). The default value is 0x8870.
4.EFT4 Working Principle for Jumbo frame
For EFT4, Jumbo frame has no relationship with MTU, just according to the Jumbo frame type field (see topic 3). If the frame length is less than 1536 Bytes, no need to verify Jumbo frame type field; if the frame length is over than 1535
Bytes, need to verify whether the Jumbo frame type value is consistent with the value set on this board. Only when they are consistent, the Jumbo frame can be passed through, otherwise it will be discarded.
If EFT4 wants to pass the Jumbo frame, the precondition is the Jumbo frame should have Jumbo frame type field. On EFT4, we can set the type value from 0x0000 to 0xFFFF (0x8870 by default). Because the 2 Bytes of Jumbo frame type
field is behind and closed to SA, if the Jumbo frame is with VLAN info, we need to set EFT4 Jumbo type to 0x8100.
Reason of this problem can be:
1.Not correct configuration
2.Ethernet board problem
4.SCC soft problem
Jumbo Setting of EFT4
EFT4 can't support Jumbo frame setting by changing MTU. We can configure it by changing Jumbo frame type field (0x8870 by default). The commands are
:ethn-cfg-get-jumbotype //check the current value//
:ethn-cfg-set-jumbotype: bid, 0xXXXX //set the exact value(0x00000xFFFF)//
After setting, only the setting value and the value of incoming frame are consistent, the Jumbo frame can be passed, otherwise it will be discarded.
If incoming frame is with VLAN, need to set the Jumbo frame type field to 0x8870.