Last year the replication configuration was updated, with UDP 8400, this was the original values for packet size.
After this, the customer states that the replication times are longer, before the backup process ended on 9AM, and now ends around 2PM. The backups are the same size, and customer confirms that VIS is the only device using the 50MB link.
Fault rectification was performed by changing the UDP packet size to 1440.
Attached is the flow performance with UDP8440 and UDP1440
According to analyzed, the optimal packet size configuration is 1440, because the length of a IP socket in Ethernet we called MTU is 1500bytes. So the data packet should be less than this value. If the data packet is longer than 1500, it will be divided up several MTU slices, and then be transmitted to the peer, and in order to read the intact data, the peer will assemble those data slices. So the performance will be reduced.
1. Size of data packet per time = VIS replication data + VIS header of replication data + UDP/IP header of Ethernet data.
2. VIS header of replication data + UDP/IP header of Ethernet data = 60
3. Every VIS replication data size = MTU – header of VIS/UDP, so 1500-60=1440.