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Advanced TCP/IP Planning and Design

Advanced TCP/IP Planning and Design. Variable Length Subnet Mask (VLSM) Supernetting Classless Enter Domain Routing (CIDR). Variable-Length Subnet Mask. Variable-length subnet mask (VLSM) provide the capability to use different masks in a network for different segments.

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Advanced TCP/IP Planning and Design

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  1. Advanced TCP/IP Planning and Design Variable Length Subnet Mask (VLSM) Supernetting Classless Enter Domain Routing (CIDR)

  2. Variable-Length Subnet Mask • Variable-length subnet mask (VLSM) provide the capability to use different masks in a network for different segments. • Large LANs could use a high bit-mask, while a serial link could use a smaller bit-mask ( /30) for two hosts (routers). • Not all routing protocols support VLSM

  3. VLSM Case How Many IPs will be lost if one of the usable subnets was used in a Point-to-point serial connection??? 172.17.0.0/20

  4. VLSM Case 172.17.48.0/20 • How would VLSM be used to break one of the big subnets into 8 smaller subnets where each subnet would have only 512 hosts?? • How would VLSM be used to break one of the 512-host subnet into several smaller subnets that would be used exclusively for serial links??? 172.17.62.0/23

  5. VLSM Case 172.17.48.0/23 172.17.62.0/30 Subnet bits = ??? Host bits = ??? Subnet bits = ??? Host bits = ??? 172.17.0.0/20

  6. Supernetting • Supernetting groups networks into larger supernets • How: by borrowing bits from the network portion of the address. • Why: Say that you want a LAN network to have more than 254 hosts; a class C network is not sufficient. You can group two Class C networks using supernets. • Benefits: Provide more IP addresses to the LAN segment without using secondary IP addresses on the router interface. (How would this effect the ISP???) • Grouping classfull networks into supernets is considered classless routing.

  7. Supernetting Case • Networks 192.168.4.0/24 and 192.168.5.0/24 are Class C networks with a default mask of 255.255.255.0. • These two networks are the same up to 23 bits. • They are combined or supernetted, into one network—192.168.4.0/23. • The mask for the new network is 255.255.254.0 • The first host address is 192.168.4.1. • The last host address is 192.168.5.254. • The broadcast address is 192.168.5.255.

  8. Address Aggregation • A set of classfull networks can also be summarized in routing entries by creating aggregate addresses at the supernet level. The depicted figure shows how address aggregation summarizes routes • in which Router A sends only one route, 208.10.8.0/22, to its upstream router.

  9. Case • Assume, for example, that network 172.17.0.0/16 will be used in a medium- to large-sized company with nine areas. • Each area could have several sites. • How can the network be divided allowing at least 2000 nodes per area? • Each area have the following: • Two large LANs with around 1000 hosts each • Four medium LANs with 200 hosts, • Five small LANs with 20 hosts, • Reserved addresses for serial links • Available room for future medium and small LANs.

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