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Figure 20.1 |
The general form of an IP datagram with a header followed by data. The header contains information that controls where and how the datagram is to be sent. |
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Figure 20.2 |
(a) An example internet with three routers connecting four physical networks, and (b) the conceptual routing table found in router R2. Each entry in the table lists a destination network and the next hop along a route to that network. |
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Figure 20.3 |
(a) An internet of four networks and three routers with an IP address assigned to each router interface, and (b) the routing table found in the center router. Each entry in the table lists a destination, a mask, and the next hop used to reach the destination. |
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Figure 20.4 |
Fields in the IP datagram header. Both the source and destination addresses are Internet addresses. |
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Animation 09_3 |
Routers interconnect Ethernet segments by receiving and retransmitting IP datagrams carried in hardware frames; routers can limit the scope of hardware broadcasts and can interconnect network segments that use dissimilar hardware technologies. |
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Animation 15_1 |
A host uses ARP to determine the hardware address of the destination of an IP datagram. The sender broadcasts an ARP request, the destination responds with an ARP reply and the sender sends the IP datagram directly to the destination. |
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Animation 16_1 |
Hosts and routers consult routing tables to forward IP datagrams. Each host or router looks in its routing table to determine the next hop to the destination. If the routing tables are changed, IP datagrams will follow different paths to the destination. |
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Animation 16_2 |
This animation converts between 32-bit hexadecimal numbers and the fields in an IP datagram header. |
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Animation 17_1 |
In an internet, the protocol software on the source computer constructs an IP datagram and transmits it to a router by encapsulating the datagram in a hardware frame. The router extracts the datagram and retransmits it in a new hardware frame to the next router on the path to the destination; the destination extracts the original datagram from the last hardware frame and delivers the data to the application. |
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Figure 21.1 |
An IP datagram encapsulated in a hardware frame. The entire datagram resides in the frame data area. In practice, the frame format used with some technologies includes a frame trailer as well as a frame header. |
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Figure 21.2 |
An IP datagram as it appears at each step during a trip across an internet. Whenever it travels across a physical network, the datagram is encapsulated in a frame appropriate to the network. |
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Figure 21.4 |
An IP datagram divided into three fragments. Each fragment carries some data from the original datagram, and has an IP header similar to the original datagram. |
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Figure 21.5 |
An example internet in which hosts can generate datagrams that require fragmentation. Once a datagram has been fragmented, the fragments are forwarded to the final destination, which reassembles them. |
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Figure 22.1 |
The general form of an IPv6 datagram. Extension headers are optional -- the minimum datagram has a base header followed by data. |
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Figure 22.2 |
The format of an IPv6 base header. The header contains fewer fields than the IPv4 datagram header. |
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Figure 22.3 |
Two IPv6 datagrams in which (a) contains a base header plus data, and (b) contains a base header, route header, and data. The NEXT HEADER field in each header specifies the type of the item that follows. |
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Figure 22.4 |
The IPv6 options extension header. Because the size of the options header can vary from one datagram to another, the HEADER LEN field specifies the exact length. |
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Figure 22.5 |
Illustration of fragmentation in IPv6. The fragmentable part of the original datagram (a), is placed in the payload area of fragments (b, c, and d). Each fragment begins with a copy of the unfragmentable part and a fragment extension header. |
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Figure 23.2 |
Two levels of encapsulation that occur when an ICMP message is sent. The ICMP message is encapsulated in a datagram, which is encapsulated in a frame for transmission across a physical network. |
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Figure 24.1 |
The format of a UDP user datagram. Each user datagram begins with an eight octet header followed by the data being sent. |
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Figure 24.2 |
The encapsulation of a UDP message in an IP datagram. The entire UDP message, including the header and data areas resides in the data area of the IP datagram. |
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Figure 26.2 |
Illustration of basic NAT translation. NAT rewrites the source address in outgoing datagrams and the destination address in incoming datagrams. |
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Figure 40.5 |
IP-in-IP encapsulation used over a VPN. (a) A datagram, (b) the encrypted version of the datagram, and (c) the encrypted version encapsulated in another datagram for transmission across the Internet. |
