after ARP protocol in a frame, there are many 0 bytes. Does anyone know the reason for the existence of these 0 bytes?
Check the Ethernet II accordion, all the 0 are labelled as padding.
Ethernet requires that all packets be at least 60 bytes long (64 bytes if you include the Frame Check Sequence at the end), so if a packet is less than 60 bytes long (including the 14-byte Ethernet header), additional padding bytes have to be added to the end of the packet.
(Those padding bytes will not show up on packets sent by the machine running Wireshark; the padding is added by the Ethernet hardware, and packets being sent by the machine capturing the traffic are given to the program before being handed to the hardware, so they haven't been padded.)
Related
Currently I am capturing network packets using tcpreplay at a speed of 800 MBPS but I want to scale it over 5 GBPS.
I am running Joy on a server with 16GB Ram and 8 Cores
Tcpreplay Output:
`Actual: 2427978 packets (2098973496 bytes) sent in 20.98 seconds
Rated: 100003501.6 Bps, 800.02 Mbps, 115678.59 pps
Flows: 49979 flows, 2381.11 fps, 2426216 flow packets, 1756 non-flow
Statistics for network device: vth0
Successful packets: 2427978
Failed packets: 0
Truncated packets: 0
Retried packets (ENOBUFS): 0
Retried packets (EAGAIN): 0`
Total Packets Captured: 2412876
I am running Joy on 4 threads but even if I use 24 threads I am not able to see any drastic change in the capturing or receiving speed.
Joy is using af_packet with Zero Copy Ring Buffer and even Cisco mercury use the same mechanism to write packets but they claim that Mercury can write at 40 GBPS on a server-class hardware so anyone have any suggestion on this issue then please revert back.
I have some PCAPNG file, one UDP packet has Frame length 187 Bytes (1496 bits) and Data length 472 Bytes. All other packets fame length is greater than data length.
Please correct me if I'm wrong. My basic understanding is Frame length should be greater than data length because frame length includes data length.
1) Whether this packet is captured correctly ?
2) In which case this could happen ?
I found its related to fragmented packet. This case occurs when packet reassembled.
I'm not quite understanding expected total of packets sent and was wondering if i'm on the right path. I have 4 computers, A, B, C, D and they relay the message from A, so A->B->C->D and I don't count transmitting back from D. And they have a packet loss of 3%. UDP on ipv4 and message must arrive for the expected destination
Say if i was to send 1000mb along a 350 byte payload
= 1000mb = 1024*1024*1000 bytes =
1048576000 bytes / 350 = 2995931.4286 packets sent
If i also had a 3% packet loss for every 100 packets
2995931.42857 * .03/100 = 8987.7943 packet loss
Does that mean i'd compute,
2995931.42857 + 8987.7943 * 3 for each transmission by each computer for extra resubmitted packets?
-Thanks heaps
If a program running on a little endian processor writes the value 0xaabbccdd uncached to address 0, and the processor uses a 32-bit wide AXI4 bus, are bits 31-24 of WDATA 0xaa or 0xdd?
AXI does not expose byte addressable memory--it can only read or write a full data bus width (32 bits in this case). The question is how it maps addresses of byte values to data bus bits.
Section A3.4.3 of the AXI spec (rev E) discusses "byte invariant" endianness, but doesn't seem to explain the order of bytes on the data bus.
If a little endian processor writes the value 0xaabbccdd uncached to address 0 via a 32-bit wide AXI4 bus, are bits 31-24 of WDATA 0xaa or 0xdd?
31-24 bits of WDATA are 0xAA independent of processor endianness. But the order of bytes in memory is determined by the endianness. See this answer for explanation of byte-invariant endianness.
I want to know proper standard for transport streams,Some of my doubts are:
If size of PES packet is > 65536 then pes_packet_length filed should be zero ?
If PES packet size more than 65536 then do we require PES header for over flow packets ?
1) PES Length should always be 0 for the video stream, and always set to real values for any other stream. 2) no, only video streams are aloud to have packets larger than 65535.
It depends about the information carried by your PES packet: cf this very good poster by Tektronix for PES packet format.