I have two laptops [Windows 7] each connected on end of 20Mbps pipe. The MTU of the NICs is 1500bytes. Maximum pingable data size end-to-end is only 1472 bytes with DF-bit set. When I initiate a normal windows based file transfer end-to-end the throughput is 20Mbps in a single session which is really good.
However when I took some wireshark logs at the server end I noticed something interesting.
The maximum segment size [MSS] observed for each PDU is 2920 bytes [2*1460]. In fact when I remove the bandwidth capping on the last mile the single session speed increases to very good speeds of 70Mbps.
Observation - 1) DF bit is set in the packets 2) The PC-to-PC maximum pingable datagram size is 1472 with DF bit set 3) The message "TCP segment of a reassembled PDU" is being observed for each & every segment 4) Normal windows file sharing is used 5) Application is "microsoft-ds" port number 445
My question is: How can the MSS segment size be 2*1460 bytes? I feel it should be 1460bytes only. Do share your observations on the same. Attached is a snapshot of the a single packet capture, single the whole file is too big
from the fact that MTU is only 1472 bytes I guess a form of tunneling may point-to-point GRE tunneling is in use of MTU would be 1500 bytes.
the WAN device may override the DF fragment in order to be able to fragment the GRE packet that carries the user packet inside, on the other end of the link the original packet is re-assembled including the DF bit set.
As a result of the scenario described above TCP MSS can be as high as the observed value as TCP is not aware of fragmentation that happens on the external GRE packet.
the DF bit can be cleared on the external GRE packet by using policy based routing with action
With XR 4.2.0 the ASR9000 is releasing a new line of hardware models. This amongst others is the RSP440, the next generation RSP with faster switch fabric along with Typhoon based Linecards, the next generation network processor.
The Cisco EPN system incorporates a network architecture designed to consolidate multiples services on a single Multiprotocol Label Switching (MPLS) transport network. This network is designed primarily based on...
Internet security is important with the increasing attacks that are happening every day. Many internet and browsing security solutions exist, but some are not very easy to use or maybe the question is how can I enable them?