How much overhead does the IP-IP tunnel header add to an IPv4 packet?

A

IP-IP is a tunneling protocol used to encapsulate on IP packet in another IP packet. To encapsulate an IP packet using IP-IP encapsulation, an outer IP header is inserted before the packet's existing IP header. The additional IP header adds 20 bytes of overhead to the packet.

An IP-IP tunnel is a type of encapsulation mechanism that allows one IP packet to be encapsulated within another IP packet. The outer packet is typically transmitted across a network and the inner packet is delivered to its final destination through the tunnel. When an IPv4 packet is encapsulated within an IP-IP tunnel, a new header is added to the original packet to identify the tunnel endpoints and other information needed to route the packet through the tunnel.

The IP-IP tunnel header is typically 20 bytes in length, which includes the following fields:

• Version (4 bits): Specifies the version of the IP protocol used in the outer header. This is usually set to 4 for IPv4.
• Header length (4 bits): Specifies the length of the IP-IP header in 32-bit words. For the standard 20-byte header, this field would be set to 5.
• TOS (8 bits): Specifies the type of service for the outer packet.
• Total length (16 bits): Specifies the total length of the outer packet, including the header and payload.
• Identification (16 bits): Used to identify fragments of the outer packet if it needs to be fragmented during transmission.
• Flags (3 bits): Used to control fragmentation of the outer packet if needed.
• Fragment offset (13 bits): Specifies the offset of the current fragment within the original packet if it has been fragmented.
• Time to live (8 bits): Specifies the maximum number of hops the outer packet can take before being discarded.
• Protocol (8 bits): Specifies the protocol used in the inner packet, such as TCP or UDP.
• Header checksum (16 bits): Used to verify the integrity of the IP-IP header.
• Source address (32 bits): Specifies the source IP address of the tunnel endpoint.
• Destination address (32 bits): Specifies the destination IP address of the tunnel endpoint.

In summary, the IP-IP tunnel header adds 20 bytes of overhead to the original IPv4 packet.