Sem1 - Module 10 Routing Fundamentals and Subnets Review

1
Sem1 - Module 10 Routing Fundamentals and
Subnets Review
2
Routable and routed protocols

• A protocol is a set of rules that determines how
  computers communicate with each other across
  networks.
• A protocol describes the following
• The format that a message must conform to
• The way in which computers must exchange a
  message within the context of a particular
  activity
• A routed protocol allows the router to forward
  data between nodes on different networks.
• Routed Protocols
• IP (Internet Protocol)
• IPX/SPX
• AppleTalk
• DECnet
• AppleTalk
• Banyan VINES
• Xerox Network Systems (XNS)

3
IP as a routed protocol
encapsulation
4
Routable and routed protocols
As a packet travels through an internetwork to
its final destination, the Layer 2 frame headers
and trailers are removed and replaced at every
Layer 3 device. This is because Layer 2 data
units, frames, are for local addressing. Layer 3
data units, packets, are for end-to-end
addressing.
encapsulation
de-encapsulation
5
Routable and routed protocols

• As a frame is received at a router interface, the
  destination MAC address is extracted.
• The address is checked to see if the frame is
  directly addressed to the router interface, or if
  it is a broadcast.
• In either of these two cases, the frame is
  accepted. Otherwise, the frame is discarded since
  it is destined for another device on the
  collision domain.
• The accepted frame has the Cyclic Redundancy
  Check (CRC) information extracted from the frame
  trailer, and calculated to verify that the frame
  data is without error.
• If the check fails, the frame is discarded. If
  the check is valid, the frame header and trailer
  are removed and the packet is passed up to Layer
  3.
• The packet is then checked to see if it is
  actually destined for the router, or if it is to
  be routed to another device in the internetwork.
• If the destination IP address matches one of the
  router ports, the Layer 3 header is removed and
  the data is passed up to the Layer 4.

6
Routable and routed protocols

• Some protocols, such as IPX, require only a
  network number because these protocols use the
  host's MAC address for the host number.
• Other protocols, such as IP, require a complete
  address consisting of a network portion and a
  host portion.
• These protocols also require a network mask in
  order to differentiate the two numbers.
• The network address is obtained by ANDing the
  address with the network mask.
• Consider following address SNM

192.168.25.79/27 192.168.25.79
255.255.255.224 IP 11000000.
10101000.00011001.01001111 SNM 11111111.11111111
.11111111.11100000 SubNet Addr 11000000.
10101000.00011001.01000000 192.168.25.64 (Subnet
for the IP 192.168.25.79/27)
7
Anatomy of an IP packet
The IP header consists of the following Version
Indicates the version of IP currently used
four bits. If the version field is different than
the IP version of the receiving device, that
device will reject the packets. IP header length
(HLEN) Indicates the datagram header length in
32-bit words. This is the total length of all
header information, accounting for the two
variable-length header fields. Total length
Specifies the length of the entire packet in
bytes, including data and header, 16 bits. To get
the length of the data payload subtract the HLEN
from the total length.
8
Anatomy of an IP packet
The IP header consists of the following Flags
A three-bit field in which the two low-order bits
control fragmentation. One bit specifies whether
the packet can be fragmented, and the other
specifies whether the packet is the last fragment
in a series of fragmented packets. Time-to-live
(TTL) A field that specifies the number of hops
a packet may travel. This number is decreased by
one as the packet travels through a router. When
the counter reaches zero the packet is discarded.
This prevents packets from looping endlessly.
Protocol indicates which upper-layer protocol,
such as TCP or UDP, receives incoming packets
after IP processing has been completed, eight
bits. Header checksum helps ensure IP header
integrity, 16 bits.
9
Anatomy of an IP packet
The IP header consists of the following Source
address specifies the sending node IP address,
32 bits. Destination address specifies the
receiving node IP address, 32 bits. Padding
extra zeros are added to this field to ensure
that the IP header is always a multiple of 32
bits. Data contains upper-layer information,
variable length up to 64 Kb.
10
Routing

• Routing is an OSI Layer 3 function.
• The following are the two key functions of a
  router
• Routers must maintain routing tables and make
  sure other routers know of changes in the network
  topology. This function is performed using a
  routing protocol to communicate network
  information with other routers.
• When packets arrive at an interface, the router
  must use the routing table to determine where to
  send them. The router switches the packets to the
  appropriate interface, adds the necessary framing
  information for the interface, and then transmits
  the frame.
• A router is a network layer device that uses one
  or more routing metrics to determine the optimal
  path along which network traffic should be
  forwarded.

11
Routing

• Routing metrics are values used in determining
  the advantage of one route over another.
• Routing protocols use various combinations of
  metrics for determining the best path for data.
• Routed protocols transport data across a network.
• Routing protocols allow routers to choose the
  best path for data from source to destination.
• A routing protocol functions includes the
  following
• Provides processes for sharing route information
• Allows routers to communicate with other routers
  to update and maintain the routing tables

12
Routing algorithms and metrics

• Metrics can be based on a single characteristic
  of a path, or can be calculated based on several
  characteristics. The following are the metrics
  that are most commonly used by routing protocols
  
• Hop count
• The number of routers that a packet must travel
  through before reaching its destination. Each
  router the data must pass through is equal to one
  hop. A path that has a hop count of four
  indicates that data traveling along that path
  would have to pass through four routers before
  reaching its final destination. If multiple paths
  are available to a destination, the path with the
  least number of hops is preferred.

13
Routing algorithms and metrics

• Bandwidth
• The data capacity of a link. Normally, a 10-Mbps
  Ethernet link is preferable to a 64-kbps leased
  line.
• Delay
• The length of time required to move a packet
  along each link from source to destination. Delay
  depends on the bandwidth of intermediate links,
  the amount of data that can be temporarily stored
  at each router, network congestion, and physical
  distance.
• Load
• The amount of activity on a network resource such
  as a router or a link.
• Reliability
• Usually a reference to the error rate of each
  network link.

14
Routing Protocols

• Two families of routing protocols are Interior
  Gateway Protocols (IGPs) and Exterior Gateway
  Protocols (EGPs).
• IGPs can be further categorized as either
  distance-vector or link-state protocols.
• Examples of distance-vector protocols include the
  following
• Routing Information Protocol (RIP) The most
  common IGP in the Internet, RIP uses hop count as
  its only routing metric.
• Interior Gateway Routing Protocol (IGRP) This
  IGP was developed by Cisco to address issues
  associated with routing in large networks.
• Enhanced IGRP (EIGRP) This Cisco-proprietary
  IGP includes many of the features of a link-state
  routing protocol. Because of this, it has been
  called a balanced-hybrid protocol, but it is
  really an advanced distance-vector routing
  protocol.

15
Link-state Routing Protocols

• Link-state routing protocols were designed to
  overcome limitations of distance vector routing
  protocols.
• Link-state routing protocols respond quickly to
  network changes sending trigger updates only when
  a network change has occurred.
• Link-state routing protocols send periodic
  updates, known as link-state refreshes, at longer
  time intervals, such as every 30 minutes.
• Link-State Routing Protocols
• IS-IS (Intermediate System-to-Intermediate System
  )
• OSPF (Open Shortest Path First)

16
Routing versus switching

• Routing and switching might seem to perform the
  same function to the inexperienced observer.
• The primary difference is that switching occurs
  at Layer 2, the data link layer, of the OSI model
  and routing occurs at Layer 3.
• This distinction means routing and switching use
  different information in the process of moving
  data from source to destination.

17
Router vs Switches

• Another difference between switched and routed
  networks is switched networks do not block
  broadcasts.
• As a result, switches can be overwhelmed by
  broadcast storms.
• Routers block LAN broadcasts, so a broadcast
  storm only affects the broadcast domain from
  which it originated.
• Because routers block broadcasts, routers also
  provide a higher level of security and bandwidth
  control than switches.

18
Benefits of Subnetting

• More efficient use of IPs
• Increased address flexibility
• Segments Broadcast domains (smaller)
• Small amount of security

19
IPs Subnetting

• For each of the following IPs
• 172.17.2.175/26
• 101.100.10.89/25
• 219.199.101.140/28
• Identify the following
• Class
• Subnet Mask
• SN bits and useable Subnets
• Host Bits and useable IPs
• Subnet address for the IP
• Subnet Broadcast address
• Useable IPs (range)
• Major Network Address
• Major Broadcast address

20
IPs Subnetting - 219.199.101.140/28 Identify
the following
Subnet Broadcast address (Host Bits
1) 219.199.101.143 Useable IPs
(range) 219.199.101.129 ? 172.17.2.142 Major
Network Address 219.199.101.0 Major Broadcast
address 219.199.101.255

• Class
• Class C
• Subnet Mask (Host Bits 0)
• 255.255.255.240
• SN bits and useable Subnets
• 4 Subnet bits
• 24 2 14
• Host Bits and useable IPs
• 4 Host Bits
• 24 2 14
• Subnet address for the IP
• 219.199 .101.10001100
• 255.255.255 .11110000
• ---------------------------------
• 219.199.101.10000000
• 219.199.101.128

21
IPs Subnetting -172.17.2.175/26 Identify the
following

• Class
• Class B
• Subnet Mask
• 255.255.255.192
• SN bits and useable Subnets
• 10 Subnet bits
• 210 2 1022
• Host Bits and useable IPs
• 6 Host Bits
• 26 2 62
• Subnet address for the IP
• 172. 17 . 2 . 10101111
• 255.255.255 . 11000000
• ---------------------------------
• 127.17.2.10000000
• 172.17.2.128

Subnet Broadcast address 172.17.2.191 Useable
IPs (range) 172.17.2.129 ? 172.17.2.190 Major
Network Address 172.17.0.0 Major Broadcast
address 172.17.255.255
22
IPs Subnetting -101.100.10.89/25 Identify the
following

• Class
• Class A
• Subnet Mask
• 255.255.255.128
• SN bits and useable Subnets
• 17 Subnet bits
• 217 2 131070
• Host Bits and useable IPs
• 7 Host Bits
• 27 2 126
• Subnet address for the IP
• 101. 100. 10 . 01011001
• 255.255.255 . 10000000
• ---------------------------------
• 101.100.10.00000000
• 101.100.10.0

Subnet Broadcast address 101.100.10.127 Useable
IPs (range) 101.100.10.1 ? 172.17.2.126 Major
Network Address 101.0.0.0 Major Broadcast
address 101.255.255.255
23
IPs Subnetting - 219.199.101.140/28 Identify
the following

• Class
• Class C
• Subnet Mask
• 255.255.255.240
• SN bits and useable Subnets
• 4 Subnet bits
• 24 2 14
• Host Bits and useable IPs
• 4 Host Bits
• 24 2 14
• Subnet address for the IP
• 219.199 .101.10001100
• 255.255.255 .11110000
• ---------------------------------
• 219.199.101.10000000
• 219.199.101.128

Subnet Broadcast address 219.199.101.143 Useable
IPs (range) 219.199.101.129 ?
172.17.2.142 Major Network Address 219.199.101.0
Major Broadcast address 219.199.101.255
24
Host Subnet Schemes
The number of lost IP addresses with a Class C
network depends on the number of bits borrowed
for subnetting.
25
Chapter 10Test