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Classful IP AddressIP Address picture book 4

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Watch animation to learn networking.• Present IP addresses in A, B, C, D classes by byte boundary with a.4-digit form (a.b.c.d) and show how routing table does lookup.• This pictured tutorial takes screenshots from Classful IP Address Animation.• OK to republish this slide. Please use hyperlink to point to its source.

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IP Address animations1. Why IP address? Shows how IP addresses are being used when computers are transmitting messages. Each packet is tagged by a sender and a receiver's IP address.2. How Internet Forwards Packets? Computers are connected to Internet via gateway routers. Routers use routing table to make packet forwarding decisions.3. Network Address. A 32-bit IP address is divided into network ID (left bits) and host ID (right bits). Router uses network addresses to forwad packets.4. Classful IP Address. Present IP addresses in A, B, C, D classes by byte boundary with a.4-digit form (a.b.c.d) and show how routing table does lookup.5. Subnettiing - Classless IP address It uses a class B address and its 5 subnets as an examples to show how routing table lookup works with different network mask.6. VLSM Show a good subnetting design case that aggregatrd routes in a routing table. Ans show a bad case that cannot aggregate routes.

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Overview: Classful IP, routing table Animation Link

Goal: Use examples to show how classful IP addresses are being used by routers to forward packets.Topology: 3 computerrs are assigned class A, B, C addresses. They are connecred to a router R1. Steps: 1) Jack ping Rose. R1 lookup network address and forwards ping to Rose 2) Rose responds by sending an Echo back to Jack. R1 forwards it to Jack. 3) Jack ping Tom in the same network as Mary. Tom is offline. Mary recevies ping and drops it.

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Classful IP

IP address contains 4 bytes. Classful IP address use the leftmost 1, 2, or 3 bytes for network addresses.- Class A: The leftmost byte is used for network address. There are 256 class A networks. Each contains 16,777,214 host addresses. E.g., 100.4.5.6/8's network address is 100.0.0.0.0 - Class B: Two leftmost bytes are used for network address. e.g., 150.1.2.3/16's network address is 150.1.0.0.0 - Class C: The left 3 bytes are network address. There are 16,777,214 class A networks. Each contains 256 host addresses. E.g., 222.111.44.33/24, network address is 222.111.44.0

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Classful IP

IP address contains 4 bytes. Classful IP address use the leftmost 1, 2, or 3 bytes for network addresses.- Class A: The leftmost byte is used for network address. There are 256 class A networks. Each contains 16,777,214 host addresses. E.g., 100.4.5.6/8's network address is 100.0.0.0.0 - Class B: Two leftmost bytes are used for network address. e.g., 150.1.2.3/16's network address is 150.1.0.0.0 - Class C: The left 3 bytes are network address. There are 16,777,214 class A networks. Each contains 256 host addresses. E.g., 222.111.44.33/24, network address is 222.111.44.0

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Classful IP

IP address contains 4 bytes. Classful IP address use the leftmost 1, 2, or 3 bytes for network addresses.- Class A: The leftmost byte is used for network address. There are 256 class A networks. Each contains 16,777,214 host addresses. E.g., 100.4.5.6/8's network address is 100.0.0.0.0 - Class B: Two leftmost bytes are used for network address. e.g., 150.1.2.3/16's network address is 150.1.0.0.0 - Class C: The left 3 bytes are network address. There are 16,777,214 class A networks. Each contains 256 host addresses. E.g., 222.111.44.33/24, network address is 222.111.44.0

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Classful IP

IP address contains 4 bytes. Classful IP address use the leftmost 1, 2, or 3 bytes for network addresses.- Class A: The leftmost byte is used for network address. There are 256 class A networks. Each contains 16,777,214 host addresses. E.g., 100.4.5.6/8's network address is 100.0.0.0.0 - Class B: Two leftmost bytes are used for network address. e.g., 150.1.2.3/16's network address is 150.1.0.0.0 - Class C: The left 3 bytes are network address. There are 16,777,214 class A networks. Each contains 256 host addresses. E.g., 222.111.44.33/24, network address is 222.111.44.0

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Jack Ping Rose

Jack ping Rose. Ping's destiination IP address is Rose's IP address 150.1.2.3/16. This is a class B address (150 is between 128~191). It's mask is /16. It means that a 32 bit IP address is divided into two parts, the left 16 bits is network ID (150.1), the network ip address is 150.1.0.0; The right 16 bits is host ID (2.3).Note: See more IP address classification details in FAQ.

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R1 forwards ping to Mary

When R1 receives ping, it reads destination IP address (150.1.2.3/16), extracts network address (150.1.0.0/16) and uses network address to lookupop its routing table. A match is found: (150.1.0.0/16, Port2). R1 forwards ping to Port2 and delivers poing to next hop.Note: See more details in FAQ for the relastionships between IP address, class, mask, network address, routing table entry.

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Rose sends Echo to Jack

When Rose receives Ping. It responds an Echo back to Jack. Echo's destination address is Jack's IP addtress 100.4.5.6. It's the sender's address of Ping. This is a class A address (100 is between 0~127). Network mask is /8: The leftmost 8 bit is used for network ID, the rightmost 24 bit is used for host ID.

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R1 forwards Echo to Jack

When R1 receives Echo, it extracts netwrok address (100.0.0.0/8) from Echo's destination address (100.4.5.6/.8) and uses network address to lookup its routing table. A mtch is found: (100.0.0.0/8, Port1). R1 forwards Echo to Port1. Ping is delviered to next hop (Jack).

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Jack ping Tom

Jack ping Tom. Tom's IP is 222.111.44.50/24, a class C address (222 is between 192~223).When R1 receives ping, it uses Ping's destination network address 222.111.44.0/24 to lookup its routing table. A match is found: (222.111.44.0/24, Port3). R1 forwards Ping to Port3 and deliviers it to network 222.111.44.0/8.Note: Router's job is to forwards packets to next hop. It does not know whether the target host exist or not.Note: Tom and Mary (222.111.44.33/24) have the same network address 222.111.44.0/8

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Jack ping Tom

Jack ping Tom. Tom's IP is 222.111.44.50/24, a class C address (222 is between 192~223).When R1 receives ping, it uses Ping's destination network address 222.111.44.0/24 to lookup its routing table. A match is found: (222.111.44.0/24, Port3). R1 forwards Ping to Port3 and deliviers it to network 222.111.44.0/8.Note: Router's job is to forwards packets to next hop. It does not know whether the target host exist or not.Note: Tom and Mary (222.111.44.33/24) have the same network address 222.111.44.0/8

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Tom is offline

Ping is forwarded to 222.111.44.0/24 network. This is an Ethernet Local Area network. All nodes will receive this ping. In this network, Ping reaches Mary and Tom.Mary receives this ping and drops it due to mis-match.Tom is offline and drops the ping.

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FAQ1. What is IP address classes?2. How to classify IP address?3. How many host IDs and network IDs for

class A, B, C addresses?4. How to determine classes when IP

addresses are presented in binary?5. How well does classful address work?（ answers in the Comments box ）

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What is Vlabvisualland.net

• VLAB: Virtual Lab– Theory: Visualize key points of network protocols to help

beginners grasp the basic ideas quickly.– Lab: Visualize network activities with packets and router

states captured from network simulators (dynamips, packet tracer, and ns2.

– Interactively control animation: packet headers, protocol state tables.

• Vlab usage– Self learning, teaching aids, lab book.