1. Cisco – Chapter 10 - Routers IP Addressing Subnetmasking

2. American Registry for Internet Numbers Some are set aside, not to be used Class A1-126 Class B128 – 191 Class C192 – 224 Class D Class E

3. Hierarchical Addressing Telephone System –Hop 1Area Code –Hop 2Local Exchange –Hop 3Local Number IP –Network Address –Subnetwork Address –Host Address

4. Routers Layer 3 Devices –Use IP address –Make best path determination –Switch packet from incoming to outgoing port –Connect separate networks Routing sometimes referred to as Layer 3 switching

5. Router Decisions Use Routing Tables –Process is called routing the packet Decisions based on –Available paths –Traffic density –Speed of segment (bandwidth)

6. Two-tier addressing MAC address –Unique identifier for each host – Layer 2 Like your name – does not change IP address –Net.subnet.host – Layer 3 –Like your address – changes when you move Dynamicassigned as needed & temporary –Allows fewer addresses to serve large number of hosts Staticassigned by network administrator ties activity to a particular host

7. Addressing Schemes Flat (physical) –NIC card address – burned in Hierarchical (logical) –Network address assigned Subnet address determined by network administrator Host address determined by network administrator Example: Postal with zip + 4

8. Network Packet Fields Type of serviceHeader checksum Total LengthSource Address Identification Destination Address FlagsIP Options OffsetData Time to LivePadding Header Protocol

9. IP Addresses Header field – source and destination are each 32 bits –4 octets Each octet has 8 binary digits Each octet expressed as decimal equivalent of binary Usually expressed in dotted decimal form –123.0.0.0

10. Examples Class A 01111110.00000000.00000000.00000000 126.0.0.0 Class B 10111110.11110000.00000000.00000000 190.240.0.0 Class C 11000001.11111000.10000000.0 193.248.128.0

11. Network Addresses Network Portion –Network address and Subnet Address Host Portion Example: 152.128.0.0 is assigned network # 152.128.200.0 is subnet # 152.128.200.2 is subnet with host nnnnnnnn.nnnnnnnn.nnnnhhhh.hhhhhhhh

12. Broadcast Addresses Class C 194.45.45.255 Class B 134.44.255.255 Class A 123.255.255.255

13. Number of Hosts Class C –2**8 – 2 = 254 Class B –2**15 – 2 = 65,534 Class C –2**24 – 2 = 16,777,214 First address is actual network address Final address is reserved for broadcasts

14. Subnet Masks Borrow bits from HOST section of address to form subnets –Maximum bits to borrow is 2 less than total bits in Host portion of address –Minimum bits to borrow is 2 Subnets reduce size of broadcast domain A subnet mask is 32 bits long –4 octets –All 1s in network and subnet portion of address

15. Subnetting Always plan for scalability –If you need four subnets, plan 8-12 Borrow bits from the hosts portion of address –Borrow bits on the right –Assign decimal equivalent as if you used all 8 bits

16. Subnetting Outside world looks only at IP portion of address Local router resolves Subnet address using subnet mask and routes to correct subnet Number of subnets = n**2 –2 where n is the number of bits borrowed from host

17. Boolean AND – No big deal !+1 = 1 1+0 = 0 That’s all there is to it

18. Subnetting Results Lose potential hosts Maximum number is when host bits = subnet bits –Work out an example