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Wrapping up subnetting , mapping IPs to physical ports

Wrapping up subnetting , mapping IPs to physical ports. BSAD 141 Dave Novak Sources : Network + Guide to Networks, Dean 2013. Outline. Subnet review Assigning logical IPs to physical ports An example. Subnets. Class C example (4 bits prefix, 4 bits suffix)

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Wrapping up subnetting , mapping IPs to physical ports

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  1. Wrapping up subnetting, mapping IPs to physical ports BSAD 141 Dave Novak Sources: Network+ Guide to Networks, Dean 2013

  2. Outline • Subnet review • Assigning logical IPs to physical ports • An example

  3. Subnets • Class C example (4 bits prefix, 4 bits suffix) • There are 14, valid 4-bit network IDs for the subnetted class C address • CANNOT use 0000 or 1111 • The same 14, 4-bit host IDs are used on each of the 14 255.255.255.240 subnets

  4. Subnets • 255.255.255.240 = subnet mask Each 4 bit group represents a subnet and a host number on each subnet 0001 1000 0010 1001 0011 1010 0100 1011 0101 1100 0110 1101 0111 1110 Subnet 0011 has 14 hosts Subnet 1100 has 14 hosts

  5. Subnets • Host numbering on subnet not sequential from one subnet to another • Subnet #1 = 0001 • This is the NETWORK reference for Subnet #1 • host #1 on subnet #1 = 00010001 = 17 • host #2 on subnet #1 = 00010010 = 18 • host #3 on subnet #1 = 00010011 = 19 • …… • host #14 on subnet #1 = 00011110 = 30

  6. Subnets • Move on to subnet #2 • Subnet #2 = 0010 • host #1 on subnet #2 = 00100001 = 33 • host #2 on subnet #2 = 00100010 = 34 • host #3 on subnet #2 = 00100011 = 35 • ….. • host #14 on subnet #2 = 00101110 = 46

  7. Subnets • We can determine host address for each of the 14 subnets this way… • Subnet #14 = 1110 • host #1 on subnet #14 = 11100001 = 225 • host #2 on subnet #14 = 11100010 = 226 • And so on… • host #14 on subnet #14 = 11101110 = 238

  8. Subnets • IP ranges for class C network address 197.70.115.0 with mask 255.255.255.240 (supporting 14 subnets with 14 hosts each): • 1) 197.70.115.16 - .31  host ranges (.17 - .30) • 2) 197.70.115.32 - .47  host ranges (.33 - .46) • 3) 197.70.115.48 - .63  host ranges (.49 - .62) • 4) 197.70.115.64 - .79  host ranges (.65 - .78) • 5) 197.70.115.80 - .95 …

  9. Subnets • Single class C supports 254 hosts • Can’t use 00000000 or 11111111 as host addresses • But, 255.255.255.240 subnet only supports 14 subnets * 14 hosts/per subnet = 196 hosts • What happened to the rest of the IP addresses  explained by these slides • Can’t use any combinations of 0000 or 1111 for EITHER the network ID OR host ID

  10. Subnets • Subnetting is not a perfect solution (with CIDR available, subnetting may not even be considered “good”) • “Lose” potentially valid host IP addresses in the process of creating more logical networks • Can allocate addresses more effectively by subdividing the static, class-based IPv4 address space, but lose valid addresses in process

  11. IP assignment • High-level overview of concepts and technologies • Generally, not discussing specific hardware, software, or vendors • high level and generic –may be exceptions to some of the general points when specific technologies are studied in detail • Logical versus physical operations / functions • Logical functions in software are not always easily mapped to something physical

  12. IP assignment • The IP is software • IP addresses are software • Addresses are mapped to logical interface on physical device

  13. Interface Configuration • In case where network protocol stack only works with specific physical network (IPX/SPX, AppleTalk, SNA), the network interface does not need to be identified to software • Software knows what interface type is because there are no other choices • Legacy Novell network  Novell software / hardware  IPX / SPX • May not require much configuration by admin

  14. Interface Configuration • MAC address is physically associated with hardware (the NIC) • Physical interface on the NIC (the RJ45 connection on card) associated with physical address (the MAC) • Can’t be changed (short of replacing NIC) • Can’t be configured Physical interface 1 maps to Physical Address 00-E3-B9-6F-5A-EA Physical interface 2 maps to Physical Address 00-A1-B9-3D-8B-EC So on… 4-port Switch 1 2 3 4 4 interfaces  4 MAC addresses

  15. InterfaceConfiguration • TCP/IP (the network protocols stack) independent of physical network (LAN technology and topology) • IP addresses are implemented in software, not hardware (create mappings to interfaces via software) • Logical IP to physical interfaces (connection) • Admin assigns IP addresses to various interfaces

  16. Routing Interface Consider a very basic hypothetical router: one physical interface out, one physical interface in Router 1 2 Some type of outside link to Internet Switch on LAN Uplink port to router 1 2 3 4 PC 2 PC 3 PC 1

  17. Routing Interface Two router physical interfaces (#1 and #2) – LAN only “knows” about #2 Any IP address not local to LAN, goes first to router physical interface #2 and then out physical interface #1 to some other router somewhere on the Internet (ANY IP address not on LAN) In this case, 2 physical interfaces handle many different logical IP addresses Router 1 2 Some type of outside link to Internet Switch on LAN 1 2 3 4 Uplink port to router PC 2 PC 3 PC 1 Switch physical interfaces #1 - #4 map to 4 physicalMAC addresses on PCs and the router (4 physical interfaces  4 MAC addresses - 3 on PCs, 1 on router). PCs maintain ARP lookup table to map logical IP addresses to physical MAC address

  18. RoutingInterface Assume our LAN has other switches and PCs and has ownership of an unsubnetted class C address block 195.70.115.0 Anything coming in from outside going to any address in the class C block 195.70.115.0 (the network reference is 195.70.115)  comes to the LAN via physical interface #1 on the router Router Each physical interface on router also has a MAC address Each physical interface on router is mapped to a logical IP address within the 195.70.115.0 address space Router interface #1 = 195.70.115.1 mapped to 00-A5-B5-3D-2B-AA Router interface #2 = 195.70.115.2 mapped to 00-A5-B5-3A-5C-BC 1 2 Some type of outside link to Internet Switch on LAN 1 2 3 4 PC 2 PC 3 PC 1

  19. RoutingInterface Incoming packet for IP address 195.70.115.4 1st – router physical interface #1 gets packet from remote sender because some outside core routers know IP interface 195.70.115.1 handles all traffic destined for the entire 195.70.115.0 network 2nd – router examines IP address of packet, consults routing table, determines it is local and then resolves MAC address to decide where to send the packet on the LAN 195.70.115.4 = 00-A1-B9-3D-8B-EC and Forwards packet out router physical interface #2, which is mapped to IP address 195.70.115.2 3rd – in this case, everything local is forwarded out router physical interface #2 mapped to IP 195.70.115.2 to switch physical interface #4 Switch knows 00-A1-B9-3D-8B-EC goes out switch physical port #2. Destination PC 2 gets packet, reads MAC address and processes Router 1 2 Some type of outside link to Internet Switch on LAN 1 2 3 4 PC 2 PC 3 PC 1

  20. Routing Interface • Class C IP address block 195.70.115.0 • 195.70.115.0 • 195.70.115.255 • In our example, router handles many logical IP addresses on single physical interface (that is associated with one MAC address)

  21. Routing Interface • Assume we subnet using mask 255.255.255.192 • (2 bits in prefix, 6 in suffix) • Binary representation of subnet mask is 11111111.11111111.11111111.11000000

  22. Application Application Transport Transport Destination Destination Gateway Gateway 195.70.115.128 195.70.115.128 195.70.115.140 195.70.115.67 195.70.115.64 195.70.115.64 195.70.115.69 195.70.115.129 Default Default 195.70.115.129 195.70.115.65 Network Address Network Address 195.70.115.69 195.70.115.140 Based on a Class B example in TCP/IP Network Administration [online] http://www.unix.org.ua/orelly/networking/tcpip/ch02_05.htm By subnetting scheme, we know default gateway is connected to network 195.70.115.64 Source Host Destination Host Gateway or Router Destination Gateway 195.70.115.128 195.70.115.129 195.70.115.64 195.70.115.67 Default 195.70.115.65 Network Address 195.70.115.67 195.70.115.129 195.70.115.128 195.70.115.64 Default = address 195.70.115.65

  23. Summary • Subnet review • Assigning logical IPs to physical ports • An example

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