Description of the problem

A private network project uses OSN3500 equipment to provide a transmission channel for the customer's data network, the data network equipment uses H3C routers, router model: H3C SR6608

After the completion of the hardware connection, the data network tuning personnel feedback router through the transmission device ping can not be, requiring the transmission to cooperate with the check the reason.

Processing

1) The network structure is as follows:

Video monitoring equipment - Access router - Transmission OSN3500 - POS155 - Aggregation router - POS155 - Core router - Video monitoring center

(2) Ping messages do not work at all, it can be determined that a device and a link does not allow more than a fixed size of the message through, which is generally related to the maximum frame length of the Ethernet settings.

3) The network OSN3500 is configured with the N1EFS0A single board, which interfaces with the data network router through the FE electrical port. The maximum frame length of the Ethernet external port is set to 1522 by default, that is, the maximum size of the IP packet that can pass through is 1522 bytes....

(4) When the user message length exceeds the set maximum frame length, the message will be discarded or intercepted as small as the set frame length. the maximum frame length needs to be set according to the actual situation in the application, and if the user does not have any special requirements, the default value of 1522 is used, which is the same as the VLAN frame length of 802.1Q.

(5) EthernetII frame structure: DMAC+SMAC+Type+Data+CRC ( 6-byte destination MAC + 6-byte source MAC + 2-byte type + 1500-byte load + 4-byte CRC = 1518 bytes, see the annex), if the Ethernet packet is labeled with Layer 1 tag, then the maximum frame length should be set to 1522, if the Ethernet packet is labeled with Layer 2 tag, then the maximum frame length should be set to 1522. If the Ethernet message is labeled with Layer 2, the maximum frame length should be set to 1526.

Root Cause

Messages exceeding the maximum frame length setting causing the ball to be dropped

Solution

1. Check that the maximum frame length of the external port of EFS0A, the EOS single board of OSN3500, is 1522 by default.

2. Communicate with H3C engineers and learn that the H3C router is configured with MPLS L3 VPN, i.e., there are two layers of labels, which means that 8 bytes are added to the 1518 bytes of the Ethernet frame, and the frame length is 1526.

3, the OSN3500 N1EFS0A single board of the corresponding external port maximum frame length parameter change to 1526 (see attached), H3C router can ping through, the problem is solved.

Suggestions and Summary

1) Ethernet frames need to be increased by 4 bytes (1522) if the IP packet is encapsulated with VLAN tagging, or by 8 bytes (1526) if it is a QinQ scenario.

2) If the IP packet is encapsulated with MPLS label, 4 bytes need to be added for each layer of label, in this case, it is MPLS L3 VPN scenario with two layers of label encapsulated, and 8 bytes need to be added to the Ethernet frame (1526).

3) If the maximum frame length is set too small and the message size is large, the message will be discarded when it is not fragmented, and if the maximum frame length is configured too large, it may result in slower transmission of the message. Therefore, the maximum frame length needs to be set according to the actual situation in the application to ensure efficient transmission of customer data.

The related technical information in this chapter and the troubleshooting process of SDH equipment are collected and organized by Shenzhen Optical Transmission Network Technology Company Limited ( www.opticaltrans.com), please retain! Our company specializes in Huawei SDH optical transmission equipment, SDH transmission equipment sales.