Hi, when i try to stream a video i can see it lagging, when i try to capture using wire-shark. i saw a lot retransmission and duplicate ack? so my question is , if i have a lot fragment or miss match MTU where by the switch are using Long Frame Size(Bytes) : 9216 while my firewall only using MTU 1500, can this be the cause of the high retransmission? and causing the lagging? asked 02 May '13, 02:38  splibytes |
One Answer:
Every system on the same physical LAN segment MUST use the same MTU size. However, it is allowed to have multiple segments (separated by a router or L3 switch or any other routing device like a loadbalancer or firewall) with different MTU sizes, however, this will result in fragmentation at the IP layer which you will want to avoid. In short, unless there is a real need for jumbo frames in a particular part of your network (storage for instance), don't use a MTU other than 1500. (I assumed you are on an ethernet network btw :-)) answered 02 May '13, 02:48  SYN-bit ♦♦ Hi, i check in one of the switch spec and found this Maximum Frame Size 1553 bytes (10/100 Mbps) 9216 bytes (1/10 Gbps) was frame size same as mtu, what i can found is that my firewall are using mtu1500 and look like the switch are using different mtu (maximum frame size) strangely, i saw a lot retransmission when ever i on video streaming such as you tube. (02 May '13, 03:42) splibytes If it is listed in the spec as maximum frame size, it is not necessarily configured to use that maximum. I doubt the retransmissions are caused by a MTU size mismatch as I assume your client receiving the video stream is connected to the switch, which is connected to the firewall, which is connected to the Internet. So the videostream in coming in from the firewall over the switch to your client. Then every frame sent by the firewall will be small enough to fit your network segment. Have you looked at duplex mismatches? Those can be a big source of retransmissions... (02 May '13, 03:52) SYN-bit ♦♦ |
can you please post a sample capture file somewhere (google docs, dropbox, cloudshark)?