#Wireshark ip id windows

When a client is initialized for the first time after it is configured to receive DHCP information, it initiates a conversation with the server.īelow is a summary table of the conversation between client and server, which is followed by a packet-level description of the process: Source Dest Source Dest Packet The following Microsoft server operating systems provide DHCP server functionality:

#Wireshark ip id windows

Microsoft TCP/IP-32 for Windows for Workgroups versions 3.11, 3.11a, and 3.11bĭifferent DHCP clients support different options that they can receive from the DHCP server. Microsoft LAN Manager Client version 2.2c for MS-DOS Microsoft Network Client version 3.0 for MS-DOS Windows NT Workstation versions 3.5, 3.51, and 4.0 Windows NT Server versions 3.5, 3.51, and 4.0 The following Microsoft products provide DHCP client functionality: The system administrator configures the DHCP server with the options that are parsed out to the client. Normally the DHCP server provides the client with at least this basic information:ĭefault GatewayOther information can be provided as well, such as Domain Name Service (DNS) server addresses and Windows Internet Name Service (WINS) server addresses. The TCP/IP stack would also have more complexity as it would have to keep track of not only the current sequence number, but also which ones had been used for fragmentation to ensure the uniqueness requirement.Dynamic Host Configuration Protocol (DHCP) is a standard protocol defined by RFC 1541 (which is superseded by RFC 2131) that allows a server to dynamically distribute IP addressing and configuration information to clients. Your proposed use of it (as a defacto Sequence ID) violates RFC 6864 as you are using the field for a purpose other than fragmentation. So, given that the IP stack on your hosts MUST NOT use the field for any purpose other than fragmentation, why should a properly optimised IP stack set this field for unfragmented packets when it is not used? The caveat that a sender MAY set any value is to accomodate older implementations that did not follow the earlier standards properly where the ID had to be unique for each SRC-DST-Protocol tuple, which would have limited throughput to about 6.4 Mbps with standard packet lifetimes. You have hit the nail on the head with your reference to RFC 6864 – the identification field MUST NOT be used for any purpose other than fragmentation (and reassembly). Wouldn’t it be nice temporarily copy ip identification field value to the outside header of an ESP packet or a way to let the troubleshooter match the clear text packet and encrypted one.

In my humble opinion, this field should never have zero value at least not for me:) and Linux should have a sysctl switch to disable this behaviour.Įspecially if you have an IPSEC VPN connection and you need to take a packet capture, you have almost no way to make a comparison between packet captures. RFC also touches on the performance impact of uniqueness of ID field for a given source/destination. RFC doesn’t enforce anything on the value and also states that originating source MAY set the field of atomic datagrams to any value. > The IPv4 ID field MUST NOT be used for purposes other than Here is the text that I really didn’t like on this RFC When I was searching some documentation to find the reason for this zero ID, I have found a very recent RFC Updated Specification of the IPv4 ID Field. I have searched for a way to disable this zero ID feature to make it unique in Linux but there doesn’t seem to exist any way. If you have multiple SYN-ACKs from the same source your Seq,Ack numbers will also be the same which means you have literally no way to distinguish two packets apart from timing. Following captured packet is a SYN-ACK segment from a Linux box.Īnd Identification field is 0. I didn’t know that this field can be zero till I notice it in a flow trace. Also it is a crucial field for me to find the right packet in the flow trace. IP ID is a field I use to compare captures taken at different segments most of the time. Especially if you need to analyze thousands of packets in packet captures or lines of flow traces.

I must say that network troubleshooting is not an easy task.