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Does Nat modify TCP header?
Yes. NATs modify both, and routers only modify the IP header checksum.
What fields does NAT change?
NAT changes the source or destination IP addresses and/or port numbers, depending on how you have NAT configured. There are various ways of using NAT, and what gets changed depends on the NAT method. Changing anything in the packet header requires the Header Checksum field to be recalculated.
Do TCP packets have IP headers?
Figure 6.1 is a graphical representation of TCP and IP headers. Both header types are at least 20 bytes long and are usually shown in 32-bit (4-byte) sections with the addresses, options, and other settings for the session.
What information does a TCP IP packet header contains?
Each IP packet contains both a header (20 or 24 bytes long) and data (variable length). The header includes the IP addresses of the source and destination, plus other fields that help to route the packet. The data is the actual content, such as a string of letters or part of a webpage.
What is the protocol field in the IP header?
The protocol field in the IP header indicates that the ICMP header will follow the IP header. The assigned value for ICMP in this field is 1 (decimal). (Novell’s LANalyzer for Windows automatically translates this value of 1 to ICMP.) The structure of the ICMP packet depends on the type of information being exchanged and the function of the packet.
How does the ICMP header work in IPv4?
An ICMP header follows the IPv4 datagram header. The value “1” in 8-bit “Protocol” field in an IPv4 datagram header indicates that the ICMP header follows the IPv4 datagram header. ICMP header has two parts. The first four bytes are available for all types of ICMP messages.
What kind of packet header does a TCP / IP use?
TCP/IP Packet Headers. Most networks uses IP version 4 (IPv4), but a newer 128-bit IP system called IP version 6 (IPv6) has been circulating for several years and has been gradually gaining acceptance. IPv6 is supposed to solve the IP address space problem by allowing up to 128 bits for the address portion.
Which is part of the ICMP packet depends on the message type?
The contents of the remaining part of ICMP packet depends on the ICMP message type. For example; ID (identifier) and SEQUENCE (sequence number) fields are the next four bytes (32 bits) after Type, Code and Checksum fields in an Echo Request and Echo reply ICMP message.