What is the value in the Identification field and the TTL field?ĩ. The value of the identification field is incremented by 1 on every new outgoing message.Ĩ. Describe the pattern you see in the values in the Identification field of the IP datagram. The fragment number, sequence number, flags, total length and checksum very from each segment so they change.ħ.
Header length and time to live stay constant because these are preset. Which fields stay constant? Which of the fields must stay constant? Which fields The checksum always changes and so does the sequence numberĦ. Within this series of ICMP messages sent by your computer? Which fields in the IP datagram always change from one datagram to the next I know this because the more fragments bit has not been set.ĥ. This IP datagram has not been fragmented. Has this IP datagram been fragmented? Explain how you determined whether or Payload = Total Length: 56 – header length:20 = 36 bytes.Ĥ. IP datagram? Explain how you determined the number of payload bytes. How many bytes are in the IP header? How many bytes are in the payload of the.Within the IP packet header, what is the value in the upper layer protocol field?.What is the IP address of your computer?.Technically, an atomic datagram is defined in RFC 6864 as: The Don't Fragment bit is set, the More Fragments bit is not set, and the Fragment Offset is 0.
They can put any value, but if they aren't going to increment to the next IP ID value, they generally put zero.Īll IPv4 hosts are required to handle IP datagrams of at least 576 bytes, so IP datagrams that are 576 bytes or less also will not be fragmented, regardless of whether the Don't Fragment bit is set or not, so some hosts will also put zero in the IP ID field if the packet is 576 bytes or less, although that case is not discussed in RFC 6864.
So, there are some IPv4 hosts that continue to increment the IP ID field in atomic datagrams, regardless of the fact that the field is meaningless in those packets, and, as you see, there are other hosts that just put zero in the IP ID field. In section 4.1 it states "In atomic datagrams, the IPv4 ID field has no meaning thus, it can be set to an arbitrary value." So, they haven't been fragmented and they won't be fragmented. RFC 6864, " Updated Specification of the IPv4 ID field," in section 4 defines "atomic datagrams" as "datagrams not yet fragmented and for which further fragmentation has been inhibited." That is, further fragmentation has been inhibited by setting the Don't Fragment bit.
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