Chapter 14
Routing Protocols
RIP, OSPF, BGP
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Figure 14-1
Autonomous systems
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Figure 14-2
Popular routing protocols
Distance Vector
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Link State
Path Vector
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Distance Vector Routing.
Forouzan + CCNA:
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Slow convergence.
Routing loops.
Counting to infinity.
Split horizon
Route poisoning.
Triggered update.
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14.3
RIP:
Routing
Information
Protocol
Exposición equipo 5
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Example of updating a routing
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Initial routing tables in a small
autonomous system
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Final routing tables for the previous figure
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RIP message format
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Request messages
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Example 1
What is the periodic response sent by router
R1 in Figure 13.8 (next slide)? Assume R1
knows about the whole autonomous system.
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Example 1
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Solution
R1 can advertise three networks 144.2.7.0,
144.2.9.0, and 144.2.12.0. The periodic response
(update packet) is shown in Figure 13.9 (next
slide).
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Solution to Example 1
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RIP timers
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Example 2
A routing table has 20 entries. It does not
receive information about five routes for 200
seconds. How many timers are running at
this time?
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Solution
The timers are listed below:
Periodic timer: 1
Expiration timer: 20 - 5 = 15
Garbage collection timer: 5
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Slow convergence
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Hop count
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Instability
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Split horizon
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Poison reverse
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RIP-v2 Format
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RIP version 2 supports
CIDR.
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Authentication
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RIP uses the services of UDP
on well-known port 520.
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14.5
OSPF:
Open Shortest
Path First
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Areas in an autonomous system
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Types of links
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Point-to-point link
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Transient link
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Stub link
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Example of an internet
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Graphical representation of an internet
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Types of LSAs
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Router link
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Network link
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Summary link to network
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Summary link to AS boundary router
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External link
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Example 3
In Figure 14.31 (next slide), which router(s)
sends out router link LSAs?
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Figure 14-31
Example 3 and Example 4
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Solution
All routers advertise router link LSAs.
R1 has two links, Net1 and Net2.
R2 has one link, Net2 in this AS.
R3 has two links, Net2 and Net3.
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Example 4
In Figure 14.31, which router(s) sends out
the network link LSAs?
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Solution
All three network must advertise network links:
Advertisement for Net1 is done by R1 because it is
the only router and therefore the designated router.
Advertisement for Net2 can be done by either R1,
R2, or R3, depending on which one is chosen as
the designated router.
Advertisement for Net3 is done by R3 because it is
the only router and therefore the designated router.
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In OSPF, all routers have
the same link state database.
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Shortest path calculation
Dijkstra algorithm
Start
Set root to local node and
move it to tentative list
Tentative list
is empty?
Yes
No
Among nodes in tentative list, move the one
with the shortest path to permanent list.
Add each unprocessed neighbor of last
moved node to tentative list if not already
There. If neighbor is in the tentative list
with larger cumulative cost, replace with
new one.
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Stop
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Shortest path calculation
Dijkstra algorithm
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Types of OSPF packets
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OSPF packet header
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Hello packet
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Database description packet
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Link state request packet
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Link state update packet
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LSA header
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Router link LSA
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Example 5
Give the router link LSA sent by router
10.24.7.9 in Figure 14.41.
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Figure 14-41
Example 5
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Solution
This router has three links: two of type 1 (point-topoint) and one of type 3 (stub network). Figure
14.42 shows the router link LSA.
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Figure 14-42
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Solution to Example 5
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Network link advertisement format
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Example 6
Give the network link LSA in Figure 14.44.
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Figure 14-44
Example 6
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Solution
The network, for which the network link
advertises, has three routers attached. The LSA
shows the mask and the router addresses. See
Figure 14.45.
Note that only one of the routers, the designated
router, advertises the network link.
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Figure 14-45
Solution to Example 6
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Summary link to network LSA
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Summary link to AS boundary LSA
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External link LSA
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Link state acknowledgment packet
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OSPF packets are
encapsulated in IP datagrams.
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