1
Anatomy of an IP Packet
IP packets consist of the data from upper layers plus an IP header. The IP header
consists of the following:
2
Routing Protocol
Router
Switch
Router
Router
Router
Switch
Router
What is
an optimal
route ?
3
Path Determination Graphic
4
Routing Protocols
Routing protocols
includes the following:
processes for sharing
route information allows
routers to communicate
with other routers to
update and maintain the
routing tables
Examples of routing
protocols that support the
IP routed protocol are:
RIP, IGRP,
OSPF, BGP,
and EIGRP.
5
Routed Protocols
Protocols used at the network layer that transfer data from one host to another across a router are called
routed or routable protocols. The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX)
are examples of routed protocols. Routers use routing protocols to exchange routing tables and share
routing information. In other words, routing protocols enable routers to route routed protocols.
6
Dynamic Routing Protocols
• Function(s) of Dynamic Routing Protocols:
–-Dynamically share information between
routers.
–-Automatically update routing table when
topology changes.
–-Determine best path to a destination.
Dynamic Routing Protocols
• The purpose of a dynamic routing protocol is to:
–-Discover remote networks
–-Maintaining up-to-date routing information
–-Choosing the best path to destination networks
–-Ability to find a new best path if the current path is
no longer available
Dynamic Routing Protocols
• Components of a routing protocol
–Algorithm
• In the case of a routing protocol algorithms are used for
facilitating routing information and best path determination
–Routing protocol messages
• These are messages for discovering neighbors and exchange of
routing information
Static Routing
Static routing algorithms are basically table mappings established by
the network administrator before the beginning of routing. These
mappings do not change unless the network administrator alters
them.
Algorithms that use static routes are simple to design and work well
in environments where network traffic is relatively predictable and
where network design is relatively simple. Because of this fact, static
routing systems cannot react to network changes.
Static routes remain in the routing table even if the specified
gateway becomes unavailable. If the
specified gateway becomes unavailable, you need to remove the
static route from the routing table
manually. However, static routes are removed from th
e routing table if the specified interface goes down,
and are reinstated
when the interface comes back up.
Static Routing
• Advantages of static routing
–-It can backup multiple interfaces/networks on
a router
–-Easy to configure
–-No extra resources are needed
–-More secure
• Disadvantages of static routing
–-Network changes require manual
reconfiguration
–-Does not scale well in large topologies
Configuring Static Routes
Static routes are table mappings established by the network administrator before
the beginning of routing. These mappings do not change unless the network
administrator alters them.
A static route uses this format:
route if_name dest_ip mask gateway_ip [distance]
Example:
hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.1 [1]
12
Configuring Default Routes
Default routes are used to route packets with destinations that do not match any
of the other routes in the routing table.
A default route is actually a special static route that uses this format:
ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]
This is sometimes referred to as a “Quad-Zero” route.
Example using next hop address:
Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1
Example using the exit interface:
Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0
13
Verifying Static
Route Configuration
After static routes are configured it is important to verify that they
are present in the routing table and that routing is working as
expected.
The command show running-config is used to view the active
configuration in RAM to verify that the static route was entered
correctly.
The show ip route command is used to make sure that the static
route is present in the routing table.
14
Classifying Routing Protocols
• Dynamic routing protocols are grouped according to characteristics.
Examples include:
–-RIP
–-IGRP
–-EIGRP
–-OSPF
–-IS-IS
–-BGP
• Autonomous System is a group of routers under the control of a
single authority.
Classifying Routing Protocols
• Types of routing protocols:
–-Interior Gateway Protocols (IGP)
–-Exterior Gateway Protocols (EGP)
Classifying Routing Protocols
• Interior Gateway Routing Protocols (IGP)
–-Used for routing inside an autonomous
system & used to route within the individual
networks themselves.
–-Examples: RIP, EIGRP, OSPF
• Exterior Routing Protocols (EGP)
–-Used for routing between autonomous
systems
–-Example: BGPv4
Autonomous System
An Autonomous System (AS) is a group of IP networks, which has a
single and clearly defined external routing policy.
EGP
Exterior Gateway
Protocols are used
for routing between
Autonomous Systems
AS 1000
AS 3000
IGP
AS 2000
Interior Gateway Protocols are
used for routing decisions
within an Autonomous System.
18
Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)
Interior Gateway Protocol
(IGP)
Exterior Gateway
Protocol (EGP)
Interior Gateway Protocol
(IGP)
AS 1000
AS 3000
EGP
EGP
IGP
EGP
AS 2000
19
Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)
IGP and EGP
An autonomous system is a network or set of networks under common
administrative control, such as the cisco.com domain.
20
Classifying Routing Protocols
• IGP: Comparison of Distance Vector & Link
State Routing Protocols
–Distance vector
– routes are advertised as vectors
– of distance & direction.
– incomplete view of network
– topology.
–Generally, periodic
– updates.
–Link state
– complete view of network
– topology is created.
– updates are not
– periodic.
–
Classifying Routing Protocols
Classifying Routing Protocols
• Classful routing
protocols
–Do NOT send subnet
mask in routing updates
• Classless routing
protocols
–Do send subnet mask
in
–routing updates.
Classifying Routing Protocols
• Convergence is defined as when all routers’
routing tables are at a state of consistency
Routing Protocols Metrics
• Metric
–A value used by a routing protocol to determine which
routes are better than others.
Routing Protocols Metrics
• Metrics used in IP routing protocols
–-Bandwidth
–-Cost
–-Delay
–-Hop count
–-Load
–-Reliability
Routing Protocols Metrics
• The Metric Field in
the Routing Table
• Metric used for each
routing protocol
–-RIP - hop count
–-IGRP & EIGRP Bandwidth (used by
default), Delay (used
by default), Load,
Reliability
–-IS-IS & OSPF – Cost,
Bandwidth (Cisco’s
implementation)
Routing Protocols Metrics
• Load balancing
–This is the ability of a router to distribute packets among
multiple same cost paths
Administrative Distance of a Route
• Purpose of a metric
–It’s a calculated value used to determine the best
path to a destination
• Purpose of Administrative Distance
–It’s a numeric value that specifies the preference
of a particular route
Administrative Distance of a Route
• Identifying the Administrative Distance (AD)
in a routing table
–It is the first number in the brackets in the
routing table
Administrative Distance of a Route
• Dynamic Routing Protocols
Administrative Distance of a Route
• Directly connected routes
–Have a default AD of 0
• Static Routes
–Administrative distance of a static route has a
default value of 1
Administrative Distance of a Route
• Directly connected routes
–-Immediately appear in the routing table as
soon as the interface is configured
Categories of Routing Protocols
Most routing algorithms can be classified into one of two categories:
•
•
distance vector
link-state
The distance vector routing approach determines the direction (vector) and
distance to any link in the internetwork.
The link-state approach, also called shortest path first, recreates the exact
topology of the entire internetwork.
34
Distance Vector
Routing Concepts
35
Distance Vector Routing (DVR)
Destination
Distance
192.16.1.0
1
192.16.5.0
1
192.16.7.0
2
Routing table contains the addresses
of destinations and the distance
of the way to this destination.
2 Hops
1 Hop
Router A
192.16.1.0
1 Hop
Router B
Flow of routing
information
Router C
Router D
192.16.7.0
192.16.5.0
36
Routing Tables Graphic
37
Distance Vector
Topology Changes
38
Router Metric Components
39
Distance Vector Routing (DVR)
192.16.3.0
192.16.2.0
192.16.6.0
Router A
Router B
Router C
Router D
192.16.4.0
192.16.7.0
192.16.1.0
192.16.5.0
L
192.16.1.0
0
L
192.16.2.0
0
L
192.16.4.0
0
L
192.16.6.0
0
L
192.16.2.0
0
L
192.16.3.0
0
L
192.16.5.0
0
L
192.16.7.0
0
L
192.16.4.0
0
L
192.16.6.0
0
L
192.16.1.0
0
L
192.16.2.0
0
L
192.16.4.0
0
L
192.16.6.0
0
L
192.16.2.0
0
L
192.16.3.0
0
L
192.16.5.0
0
L
192.16.7.0
0
L
192.16.3.0
1
B
192.16.4.0
0
L
192.16.6.0
0
L
192.16.5.0
1
C
192.16.4.0
1
B
192.16.1.0
1
A
192.16.3.0
1
B
192.16.4.0
1
C
192.16.5.0
1
C
192.16.2.0
1
B
192.16.6.0
1
C
192.16.7.0
1
D
Locally connected
40
Distance Vector Routing (DVR)
192.16.1.0
0
L
192.16.2.0
0
L
192.16.4.0
0
L
192.16.6.0
0
L
192.16.2.0
0
L
192.16.3.0
0
L
192.16.5.0
0
L
192.16.7.0
0
L
192.16.3.0
1
B
192.16.4.0
0
L
192.16.6.0
0
L
192.16.5.0
1
C
192.16.4.0
1
B
192.16.1.0
1
A
192.16.3.0
1
B
192.16.4.0
1
C
192.16.5.0
2
B
192.16.5.0
1
C
192.16.2.0
1
B
192.16.3.0
2
C
192.16.6.0
2
B
192.16.6.0
1
C
192.16.7.0
1
D
192.16.2.0
2
C
192.16.7.0
2
C
192.16.1.0
2
B
192.16.1.0
0
L
192.16.2.0
0
L
192.16.4.0
0
L
192.16.6.0
0
L
192.16.2.0
0
L
192.16.3.0
0
L
192.16.5.0
0
L
192.16.7.0
0
L
192.16.3.0
1
B
192.16.4.0
0
L
192.16.6.0
0
L
192.16.5.0
1
C
192.16.4.0
1
B
192.16.1.0
1
A
192.16.3.0
1
B
192.16.4.0
1
C
192.16.5.0
2
B
192.16.5.0
1
C
192.16.2.0
1
B
192.16.3.0
2
C
192.16.6.0
2
B
192.16.6.0
1
C
192.16.7.0
1
D
192.16.2.0
2
C
192.16.7.0
3
B
192.16.7.0
2
C
192.16.1.0
2
B
192.16.1.0
3
C
41
Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)
Link State Routing protocol
Link State Concepts
43
Link State Topology Changes
44
Link State Routing (LSR)
LSP:
„My links to
R2 and R4 are up“
LSP:
„My links to R1 and R3 are up.
My link to R2 is down.“
SPF
Routing
Table
Router 4
Router 1
Router 2
LSP: „My links to
R1 and R3 are up,
my link to R4 is down.“
LSP....link state packet
SPF... shortest path first
Router 3
LSP: „My links to
R2 and R4 are up.“
45
Link State Concerns
46
Link State Routing (LSR)
1
Router A
4
Router C
2
2
Router E
1
4
Router B
Router D
Link State Database
B-2
C-1
A-2
D-4
A-1
D-2
E-4
C-2
B-4
E-1
C-4
D-1
Router A
Router B
Router C
Router D
Router E
A
B
B
C
D
C
A
D
D
A
D
C
E
E
B
E
E
C
B
A
47
Link State Routing Features
Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms.
Link-state routing algorithms maintain a complex database of topology information.
The distance vector algorithm are also known as Bellman-Ford algorithms. They have nonspecific information
about distant networks and no knowledge of distant routers.
A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. Linkstate routing uses:
•
Link-state advertisements (LSAs)
A link-state advertisement (LSA) is a small packet of routing information
that is sent between routers.
•
Topological database
A topological database is a collection of information gathered from LSAs.
•
SPF algorithm
The shortest path first (SPF) algorithm is a calculation performed on the
database resulting in the SPF tree.
•
Routing tables – A list of the known paths and interfaces.
48
Link State Routing
49
Comparing Routing Methods
50
Questions
?