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The IP header starts with version (4 bits) and IHL (4 bits). The following IP packet shows the hex "c2 c2 0c 0c" at the beginning of the packet. That means "C" represents IPv4. But how does a hex "C" get translated into IPv4? What would the hex number be if the packet is IPv6? Then we see "2" for IHL. What IP header length does "2" translate to?
This field identifies the IP version of the packet. This is the 4th bit value set to be binary 0100 (0+4+0+0) for IPv4 packet or 0110 (0+4+2+0) for IPv6 packet. This is the 4th bit field specifying the length of the IP header. Here in our example, it is the minimum value of 20 Bytes since we are not using any option field.
The IP packet is carrying (encapsulating) some data in its payload. It could be a TCP segment, a UDP packet, an ICMP message, an EIGRP update, etc. When IP receives the packet from the link layer it will process it and when it's finished it needs to remove the IP header and pass the payload to the next process that the payload is meant for.
Hi! Internet Header Length – Indicates the number of 4-byte blocks in the IPv4 header. The size of this field is 4 bits. Because an IPv4 header is a minimum of 20 bytes in size, the smallest value of the Internet Header Length (IHL) field is 5. IPv4 options can extend the minimum IPv4 header size in increments of 4 bytes.
Generally, Padding is basically used to make sure that the IP packet header has a length that is a multiple of 32 bits. It is needed because of the varying length of the options field in the IP header. The internet header padding is used to ensure that the internet header ends on a 32 bit. In the IPv4 Packet Header, there is an options field.
An IP header is limited to maximum of 15, 32 bit words (15 *4 = 60 bytes) and minimum of 5 ( 5 * 4 = 20 bytes) 32 bit words. What you see above are 5, 32 bit words, which is the minimum. The remaining 40 bytes (15 - 5 = 10 * 4 = 40 bytes) in the IP header are used if options are present. Expand Post.
Yeah after you said I checked about that. And found out for TCP checksum only a part of IP header (pseudo header) is used which contains values that don't change across the path from source to destination. So, does that mean, destination hosts don't drop IP packets even if something has been changed other than those fixed values.
IP Header Checksum Calculation Issue. IP header checksum is 16 bit one’s complement of the one’s complement sum of all 16 bit words in the header. To calculate IP header checksum, we should divide IP header into portions of 16 bits (or 4 hex), and sum each of them up (excluding Header checksum field - 3a42) 4500 -> 0100 0101 0000 0000.
Hence, maximum number of 4-byte words is 16. 16x4 = 64 bytes or 512 bits. deduct minimum IP header without options which is 20 bytes and you end up with 44 bytes or 352 bits available for options. I think you confused the IHL field length with its default value of 5. 5 4-byte words makes up to 20 bytes, which is the default IP header length ...
The IP MTU command on the tunnel interface can be used to change the size of the IP packet. By default the router automatically calculates the IP MTU size based on the outgoing physical interface. For eg. the physical interface has an MTU of 1000 bytes: R2#show int e0/0 | in MTU.