Cisco – Chapter 10 - Routers IP Addressing Subnetmasking

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

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

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

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

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

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

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

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 –

Examples Class A Class B Class C

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

Broadcast Addresses Class C Class B Class A

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

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

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

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

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

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