Week Nine Attendance Announcements Happy with the midterm exam
scores Review question(s) on midterm exam Final exam more questions
and questions specific Review Week Eight Information Current Week
Information Upcoming Assignments
Slide 3
Midterm Exam Question Question 134 The first step in the design
process should be predocumenting the design requirements and
reviewing them with the customer for verification and approval,
obtaining direct customer input, in either oral or written form.
Identify the predocumenting procedures. Answer: Sifting,
translating, processing, and reordering
Slide 4
Week Eight Topics 1.NAT Overload 2.CIDR 3.Classful and classful
4.IPv6 Standard 5.IPv6 Transition 6.Routing Protocols
Slide 5
IP Address Historical classful network architecture Class
Leading address bits Range of first octet Format Network ID Format
Host ID Format Number of networks Number of addresses Class A 0 0 -
127 a b.c.d 2 7 = 128 2 24 = 16777216 Class B 10 128 - 191 a.b c.d
2 14 = 16384 2 16 = 65536 Class C 110 192 223 a.b.c d 2 21 =
2097152 2 8 = 256 Fields defined below. 1.Leading address bits
2.Range of first octet 3.Network ID format 4.Host ID format
5.Number of networks 6.Number of addresses
Slide 6
IP Addresses Public and Private
Slide 7
IP Addresses Public Fixed length: 32 bits Initial classful
structure (1981) Total IP address size: 4 billion Class A: 128
networks, 16M hosts Class B: 16K networks, 64K hosts Class C: 2M
networks, 256 hosts
Slide 8
Network Address Translation (NAT) What is NAT Overload? NAT
overloading (sometimes called Port Address Translation or PAT) maps
multiple private IP addresses to a single public IP address or a
few addresses. This is what most home routers do. With NAT
overloading, multiple addresses can be mapped to one or to a few
addresses because each private address is also tracked by a port
number. When a client opens a TCP/IP session, the NAT router
assigns a port number to its source address. NAT overload ensures
that clients use a different TCP port number for each client
session with a server on the Interne
Slide 9
NAT Terminology
Slide 10
Slide 11
Classless Interdomain Routing (CIDR) What is CIDR? CIDR is a
new addressing scheme for the Internet which allows for more
efficient allocation of IP addresses than the old Class A, B, and C
address scheme. Why Do We Need CIDR? With a new network being
connected to the Internet every 30 minutes the Internet was faced
with two critical problems: Running out of IP addresses Running out
of capacity in the global routing tables
Slide 12
Classless Inter-Domain Routing (CIDR) CIDR is pronounced cider
With CIDR, addresses use bit identifiers, or bit masks, instead of
an address class to determine the network portion of an address
CIDR uses the /N notation instead of subnet masks CIDR allows for
the more efficient allocation of IP addresses
Slide 13
Classless Inter-Domain Routing (CIDR) 172.16.0.0 255.255.0.0=
172.16.0.0 /16 198.30.1.0 255.255.255.0= 198.30.1.0 /24 Note that
192.168.24.0 /22 is not a Class C network, it has a subnet mask of
255.255.252.0
Slide 14
CIDR and Route Aggregation CIDR allows routers to summarize, or
aggregate, routing information One address with a mask can
represent multiple networks This reduces the size of routing tables
Supernetting is another term for route aggregation
Slide 15
CIDR and Route Aggregation Given four Class C Networks (/24):
192.168.16.0 11000000 1010100000010000 00000000 192.168.17.0
11000000 1010100000010001 00000000 192.168.18.0 11000000
1010100000010010 00000000 192.168.19.0 11000000 1010100000010011
00000000 Identify which bits all these networks have in common.
192.168.16.0 /22 can represent all these networks. The router will
look at the first 22 bits of the address to make a routing
decision. Note that 192.168.16.0 /22 is not a Class C network, it
has a subnet mask of 255.255.252.0
Slide 16
IPv4 Address Utilization
Slide 17
Subnet Masks A major network is a Class A, B, or C network
Fixed-Length Subnet Masking (FLSM) is when all subnet masks in a
major network must be the same Variable-Length Subnet Masking
(VLSM) is when subnet masks within a major network can be
different. Some routing protocols require FLSM; others allow
VLSM
Slide 18
VLSM VLSM makes it possible to subnet with different subnet
masks and therefore results in more efficient address space
allocation. VLSM also provides a greater capability to perform
route summarization, because it allows more hierarchical levels
within an addressing plan. VLSM requires prefix length information
to be explicitly sent with each address advertised in a routing
update
Slide 19
VLSM
Slide 20
Subnet Calculator The IP Subnet Mask Calculator enables subnet
network calculations using network class, IP address, subnet mask,
subnet bits, mask bits, maximum required IP subnets and maximum
required hosts per subnet. Results of the subnet calculation
provide the hexadecimal IP address, the wildcard mask, for use with
ACL (Access Control Lists), subnet ID, broadcast address, the
subnet address range for the resulting subnet network and a subnet
bitmap. For classless supernetting, please use the CIDR Calculator.
For classful supernetting, please use the IP Supernet Calculator.
For simple ACL (Access Control List) wildcard mask calculations,
please use the ACL Wildcard Mask Calculator.CIDR CalculatorIP
Supernet CalculatorACL Wildcard Mask Calculator Note: These online
network calculators may be used totally free of charge provided
their use is from this url (www.subnet- calculator.com).
Slide 21
IP Address with Port Number Notation The : (colon) indicates
the number following is a Port Number - in the above case 369. This
format is typically only used where a service is available on a
non-standard port number, for instance, many web configuration
systems, such as Samba swat, will use a non-standard port to avoid
clashing with the standard web (HTTP) port number of 80. A port
number is 16 bits giving a decimal range of 0 to 65535. In most
systems privileged or well-known ports lie in the range 0 - 1023
and require special access rights, normal user ports lie in the
range 1024 to 65535. TCP and UDP use protocol port numbers to
distinguish among multiple applications that are running on a
single device. Example: 192.168.1.2:369
Slide 22
Classful and Classless Routing Protocols Classful routing
protocols DO NOT send subnet mask information in their routing
updates When a router receives a routing update, it simply assumes
the default subnet mask (Class A, B, or C) VLSM cannot be used in
networks that use Classful routing protocols Classless routing
protocols send the subnet mask (prefix length) in their updates
VLSM can be used with Classless routing protocols
Slide 23
IPv6 Standard Larger address space: IPv6 addresses are 128
bits, compared to IPv4s 32 bits. This larger addressing space
allows more support for addressing hierarchy levels, a much greater
number of addressable nodes, and simpler auto configuration of
addresses. Globally unique IP addresses: Every node can have a
unique global IPv6 address, which eliminates the need for NAT. Site
multi-homing: IPv6 allows hosts to have multiple IPv6 addresses and
allows networks to have multiple IPv6 prefixes. Consequently, sites
can have connections to multiple ISPs without breaking the global
routing table. Header format efficiency: A simplified header with a
fixed header size makes processing more efficient.
Slide 24
IPv6 Standard Improved privacy and security: IPsec is the IETF
standard for IP network security, available for both IPv4 and IPv6.
Although the functions are essentially identical in both
environments, IPsec is mandatory in IPv6. IPv6 also has optional
security headers. Flow labeling capability: A new capability
enables the labeling of packets belonging to particular traffic
flows for which the sender requests special handling, such as non
default quality of service (QoS) or real- time service.
Slide 25
IPv6 Standard Increased mobility and multicast capabilities:
Mobile IPv6 allows an IPv6 node to change its location on an IPv6
network and still maintain its existing connections. With Mobile
IPv6, the mobile node is always reachable through one permanent
address. A connection is established with a specific permanent
address assigned to the mobile node, and the node remains connected
no matter how many times it changes locations and addresses.
Improved global reach ability and flexibility. Better aggregation
of IP prefixes announced in routing tables.
Slide 26
IPv6 Standard Multi-homed hosts. Multi-homing is a technique to
increase the reliability of the Internet connection of an IP
network. With IPv6, a host can have multiple IP addresses over one
physical upstream link. For example, a host can connect to several
ISPs. Auto-configuration that can include Data Link layer addresses
in the address space. More plug-and-play options for more devices.
Public-to-private, end-to-end readdressing without address
translation. This makes peer-to-peer (P2P) networking more
functional and easier to deploy. Simplified mechanisms for address
renumbering and modification.
Slide 27
IPv6 Standard Better routing efficiency for performance and
forwarding-rate scalability No broadcasts and thus no potential
threat of broadcast storms No requirement for processing checksums
Simplified and more efficient extension header mechanisms Flow
labels for per-flow processing with no need to open the transport
inner packet to identify the various traffic flows
Slide 28
IPv6 Standard Movement to change from IPv4 to IPv6 has already
begun, particularly in Europe, Japan, and the Asia- Pacific region.
These areas are exhausting their allotted IPv4 addresses, which
makes IPv6 all the more attractive and necessary. In 2002, the
European Community IPv6 Task Force forged a strategic alliance to
foster IPv6 adoption worldwide. The North American IPv6 Task Force
has set out to engage the North American markets to adopt IPv6. The
first significant North American advances are coming from the U.S.
Department of Defense (DoD).
Slide 29
IPv6 Standard Using the "::" notation greatly reduces the size
of most addresses as shown. An address parser identifies the number
of missing zeros by separating any two parts of an address and
entering 0s until the 128 bits are complete
Slide 30
IPv6 Larger address Space IPv4 32 bits or 4 bytes long
4,200,000,000 possible addressable nodes IPv6 128 bits or 16 bytes:
four times the bits of IPv4 3.4 * 1038possible addressable nodes
340,282,366,920,938,463,374,607,432,768,211,456 5 * 1028addresses
per person
Slide 31
IPv6 Larger Address Space
Slide 32
IPv6 Representation x:x:x:x:x:x:x:x,where x is a 16-bit
hexadecimal field Leading zeros in a field are optional:
2031:0:130F:0:0:9C0:876A:130B Successive fields of 0 can be
represented as ::, but only once per address. Examples:
2031:0000:130F:0000:0000:09C0:876A:130B 2031:0:130f::9c0:876a:130b
FF01:0:0:0:0:0:0:1 >>> FF01::1 0:0:0:0:0:0:0:1
>>> ::1 0:0:0:0:0:0:0:0 >>> ::
Slide 33
IPv6 Addressing Model Addresses are assigned to interfaces
Change from IPv4 mode: Interface expected to have multiple
addresses Addresses have scope Link Local Unique Local Global
Addresses have lifetime Valid and preferred lifetime
Slide 34
IPv6 Address Types Unicast Address is for a single interface.
IPv6 has several types (for example, global and IPv4 mapped).
Multicast One-to-many Enables more efficient use of the network
Uses a larger address range Anycast One-to-nearest(allocated from
unicast address space). Multiple devices share the same address.
All anycast nodes should provide uniform service. Source devices
send packets to anycast address. Routers decide on closest device
to reach that destination. Suitable for load balancing and content
delivery services.
Slide 35
IPv6 Global Unicast Addresses The global unicast and the
anycast share the same address format. Uses a global routing
prefixa structure that enables aggregation upward, eventually to
the ISP. A single interface may be assigned multiple addresses of
any type (unicast, anycast, multicast). Every IPv6-enabled
interface must contain at least one loopback (::1/128)and one
link-local address. Optionally, every interface can have multiple
unique local and global addresses. Anycast address is a global
unicast address assigned to a set of interfaces (typically on
different nodes). IPv6 anycast is used for a network multihomed to
several ISPs that have multiple connections to each other.
Slide 36
IPv6 Transition Strategies The transition from IPv4 does not
require upgrades on all nodes at the same time. Many transition
mechanisms enable smooth integration of IPv4 and IPv6. Other
mechanisms that allow IPv4 nodes to communicate with IPv6 nodes are
available. Different situations demand different strategies. The
figure illustrates the richness of available transition strategies.
Recall the advice: "Dual stack where you can, tunnel where you
must." These two methods are the most common techniques to
transition from IPv4 to IPv6.
Slide 37
IPv6 Transition Strategies Dual stacking is an integration
method in which a node has implementation and connectivity to both
an IPv4 and IPv6 network. This is the recommended option and
involves running IPv4 and IPv6 at the same time. Router and
switches are configured to support both protocols, with IPv6 being
the preferred protocol.
Slide 38
IPv6 Transition Strategies Tunneling The second major
transition technique is tunneling. There are several tunneling
techniques available, including: Manual IPv6-over-IPv4 tunneling
-An IPv6 packet is encapsulated within the IPv4 protocol. This
method requires dual-stack routers. Dynamic 6to4 tunneling
-Automatically establishes the connection of IPv6 islands through
an IPv4 network, typically the Internet. It dynamically applies a
valid, unique IPv6 prefix to each IPv6 island, which enables the
fast deployment of IPv6 in a corporate network without address
retrieval from the ISPs or registries
Slide 39
IPv6 Standard
Slide 40
IPv6 Dual Stacking
Slide 41
Routing Protocols One of the primary jobs of a router is to
determine the best path to a given destination A router learns
paths, or routes, from the static configuration entered by an
administrator or dynamically from other routers, through routing
protocols
Slide 42
Routing Table Principles Three principles regarding routing
tables: 1.Every router makes its decisions alone, based on the
information it has in its routing table. 2.Different routing table
may contain different information 3.A routing table can tell how to
get to a destination but not how to get back (Asymmetric Routing)
Routing information about a path from one network to another does
not provide routing information about the reverse, or return,
path.
Slide 43
Routing Table Structure PC1 sends ping to PC2 R1 has a route to
PC2s network R2 has a route to PC2s network R3 is directly
connected to PC2s network PC2 sends a reply ping to PC1 R3 has a
route to PC1s network R2 does not have a route to PC1s network R2
drops the ping reply
Slide 44
Routing Table Structure
Slide 45
Routing Tables Routers keep a routing table in RAM A routing
table is a list of the best known available routes Routers use this
table to make decisions about how to forward a packet On a Cisco
router, the show IP route command is used to view the TCP/IP
routing table
Slide 46
Routing Table
Slide 47
A routing table maps network prefixes to an outbound interface.
When RTA receives a packet destined for 192.168.4.46, it looks for
the prefix 192.168.4.0/24 in the routing table RTA then forwards
the packet out an interface, such as Ethernet0, as directed in the
routing table
Slide 48
Routing Loops A network problem in which packets continue to be
routed in an endless circle It is caused by a router or line
failure, and the notification of the downed link has not yet
reached all the other routers It can also occur over time due to
normal growth or when networks are merged together Routing
protocols utilize various techniques to lessen the chance of a
routing loop
Slide 49
Routing Table Structure The primary function of a router is to
forward a packet toward its destination network, which is the
destination IP address of the packet. To do this, a router needs to
search the routing information stored in its routing table.
Slide 50
Routing Protocols Routing Table is stored in ram and contains
information: Directly connected networks-this occurs when a device
is connected to another router interface Remotely connected
networks-this is a network that is not directly connected to a
particular router network/next hop associations-about the networks
include source of information, network address & subnet mask,
and Ip address of next-hop router The show ip route command is used
to view a routing table on a Cisco router
Slide 51
Routing Protocols
Slide 52
Directly Connected Routes-To visit a neighbor, you only have to
go down the street on which you already live. This path is similar
to a directly-connected route because the "destination" is
available directly through your "connected interface," the
street.
Slide 53
Static Routing Static Routes-A train uses the same railroad
tracks every time for a specified route. This path is similar to a
static route because the path to the destination is always the
same.
Slide 54
Static Routing When network only consists of a few routers
Using a dynamic routing protocol in such a case does not present
any substantial benefit. Network is connected to internet only
through one ISP There is no need to use a dynamic routing protocol
across this link because the ISP represents the only exit point to
the Internet
Slide 55
Static Routing Hub & spoke topology is used on a large
network A hub-and-spoke topology consists of a central location
(the hub) and multiple branch locations (spokes), with each spoke
having only one connection to the hub. Using dynamic routing would
be unnecessary because each branch has only one path to a given
destination-through the central location. Static routing is useful
in networks that have a single path to any destination
network.
Slide 56
Static Routing Static routes in the routing table Includes:
network address and subnet mask and IP address of next hop router
or exit interface Denoted with the code S in the routing table
Routing tables must contain directly connected networks used to
connect remote networks before static or dynamic routing can be
used
Slide 57
Static Routing
Slide 58
Slide 59
When an interface goes down, all static routes mapped to that
interface are removed from the IP routing table Static routing is
not suitable for large, complex networks that include redundant
links, multiple protocols, and meshed topologies Routers in complex
networks must adapt to topology changes quickly and select the best
route from multiple candidates
Slide 60
Static Route Example The corporate network router has only one
path to the network 172.24.4.0 connected to RTY A static route is
entered on RTZ
Slide 61
Routing Protocols Dynamic Routes-When driving a car, you can
"dynamically" choose a different path based on traffic, weather, or
other conditions. This path is similar to a dynamic route because
you can choose a new path at many different points on your way to
the destination.
Slide 62
Dynamic Routing Dynamic routing protocols Are used to add
remote networks to a routing table Are used to discover networks
Are used to update and maintain routing tables
Slide 63
Dynamic Routing Automatic network discovery Network discovery
is the ability of a routing protocol to share information about the
networks that it knows about with other routers that are also using
the same routing protocol. Instead of configuring static routes to
remote networks on every router, a dynamic routing protocol allows
the routers to automatically learn about these networks from other
routers. These networks -and the best path to each network -are
added to the router's routing table and denoted as a network
learned by a specific dynamic routing protocol.
Slide 64
Dynamic Routing Maintaining routing tables Dynamic routing
protocols are used to share routing information with other routers
and to maintain an up-to-date routing table. Dynamic routing
protocols not only make a best path determination to various
networks, they will also determine a new best path if the initial
path becomes unusable (or if the topology changes)
Slide 65
Dynamic Routing
Slide 66
Configuring Dynamic Routing Dynamic routing of TCP/IP can be
implemented using one or more protocols which are often grouped
according to where they are used. Routing protocols designed to
work inside an autonomous system are categorized as interior
gateway protocols (IGPs). Protocols that work between autonomous
systems are classified as exterior gateway protocols (EGPs).
Protocols can be further categorized as either distance vector or
link-state routing protocols, depending on their method of
operation.
Slide 67
Autonomous Systems (AS) An autonomous system is one network or
sets of networks under a single administrative control. An
autonomous system might be the set of all computer networks owned
by a company, or a college. Companies and organizations might own
more than one autonomous system, but the idea is that each
autonomous system is managed independently with respect to BGP. An
autonomous system is often referred to as an 'AS'. A good example
is UUNet, who uses one autonomous system as their European network,
and a separate autonomous system for their domestic networks in the
Americas.
Slide 68
Autonomous System Number (ASN) Autonomous System Numbers (ASNs)
are globally unique numbers that are used to identify autonomous
systems (ASes) and which enable an AS to exchange exterior routing
information between neighboring ASes. An AS is a connected group of
IP networks that adhere to a single and clearly defined routing
policy.
Slide 69
Autonomous System Numbers Each AS has an identifying number
that is assigned by an Internet registry or a service provider.
This number is between 1 and 65,535. AS numbers within the range of
64,512 through 65,535are reserved for private use. This is similar
to RFC 1918 IP addresses. Because of the finite number of available
AS numbers, an organization must present justification of its need
before it will be assigned an AS number. An organization will
usually be a part of the AS of their ISP
Slide 70
Autonomous System An AS is a group of routers that share
similar routing policies and operate within a single administrative
domain. An AS can be a collection of routers running a single IGP,
or it can be a collection of routers running different protocols
all belonging to one organization. In either case, the outside
world views the entire Autonomous System as a single entity.
Slide 71
Interior Versus Exterior Routing Protocols An interior gateway
protocol (IGP) is a routing protocol that is used within an
autonomous system (AS). Two types of IGP. Distance-vector routing
protocols each router does not possess information about the full
network topology. It advertises its distances to other routers and
receives similar advertisements from other routers. Using these
routing advertisements each router populates its routing table. In
the next advertisement cycle, a router advertises updated
information from its routing table. This process continues until
the routing tables of each router converge to stable values.
Slide 72
Interior Versus Exterior Routing Protocols Distance-vector
routing protocols make routing decisions based on hop-by-hop. A
distance vector routers understanding of the network is based on
its neighbors definition of the topology, which could be referred
to as routing by rumor. Route flapping is caused by pathological
conditions (hardware errors, software errors, configuration errors,
intermittent errors in communications links, unreliable
connections, etc.) within the network which cause certain reach
ability information to be repeatedly advertised and withdrawn.
Slide 73
Interior Versus Exterior Routing Protocols In networks with
distance vector routing protocols flapping routes can trigger
routing updates with every state change. Cisco trigger updates are
sent when these state changes occur. Traditionally, distance vector
protocols do not send triggered updates.
Slide 74
Interior Versus Exterior Routing Protocols Link-state routing
protocols, each node possesses information about the complete
network topology. Each node then independently calculates the best
next hop from it for every possible destination in the network
using local information of the topology. The collection of best
next hops forms the routing table for the node. This contrasts with
distance-vector routing protocols, which work by having each node
share its routing table with its neighbors. In a link-state
protocol, the only information passed between the nodes is
information used to construct the connectivity maps.
Slide 75
Routing Protocols Interior routing protocols are designed for
use in a network that is controlled by a single organization RIPv1
RIPv2, EIGRP, OSPF and IS-IS are all Interior Gateway
Protocols
Slide 76
Link State Analogy Each router has a map of the network
However, each router looks at itself as the center of the topology
Compare this to a you are here map at the mall The map is the same,
but the perspective depends on where you are at the time You
Slide 77
Link State Analogy
Slide 78
Exterior Gateway Routing Protocol An exterior routing protocol
is designed for use between different networks that are under the
control of different organizations An exterior routing routes
traffic between autonomous systems These are typically used between
ISPs or between a company and an ISP BGPv4is the Exterior Gateway
Protocol used by all ISPs on the Internet
Slide 79
EGI and EGP Routing Protocol
Slide 80
IGP and EGP Routing Protocol Summary Distant VectorLink State
RIP (v1 and v2)OSPF EIGRP (hybrid)IS-IS
Slide 81
Routing Protocols EIGRP is an advanced distance vector protocol
that employs the best features of link-state routing.
Slide 82
What is Convergence Routers share information with each other,
but must individually recalculate their own routing tables For
individual routing tables to be accurate, all routers must have a
common view of the network topology When all routers in a network
agree on the topology they are considered to have converged
Slide 83
Why is Quick Convergence Important? When routers are in the
process of convergence, the network is susceptible to routing
problems because some routers learn that a link is down while
others incorrectly believe that the link is still up It is
virtually impossible for all routers in a network to simultaneously
detect a topology change.
Slide 84
Convergence Issues Factors affecting the convergence time
include the following: Routing protocol used Distance of the
router, or the number of hops from the point of change Number of
routers in the network that use dynamic routing protocols Bandwidth
and traffic load on communications links Load on the router Traffic
patterns in relation to the topology change
Slide 85
Routing Protocols
Slide 86
Each AS has its own set of rules and policies. The AS number
uniquely distinguish it from other ASs around the world.
Slide 87
Upcoming Deadlines Assignement 1-4-2 Phase 2: WAN Network
Design question due June 20, 2011. Assignement 10-1 Concept
Questions 7 due July 4, 2011. Assignement 1-4-3 Network Design
Project Phase 2: WAN Network Design is due July 11, 2011. Final
Exam August 1 through 6. Check the hours of operation at the
Student Learning Center.