Download - Distance Vector Protocols
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Iskra Djonova-Popova
The 4th CEENet WorkshopBratislava, Slovakia 1
Distance Vector Protocols Distance Vector Protocols (contents)(contents)
IGPs - what are they and why they are needed
Routing algorithms - the design goals
Distance vector versus Link state RIP (Routing Information Protocol)
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IGP - What Are TheyIGP - What Are They
Internal Gateway Protocols Single network administration Unique routing policy Make best use of network resources
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The 4th CEENet WorkshopBratislava, Slovakia 3
IGP - Why They are NeededIGP - Why They are Needed
A B C
D E
2
3 4
5
1
Routing algorithms would scale better
Static routes would be fine
6
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Routing Algorithms - the Routing Algorithms - the Design GoalsDesign Goals
Optimally Simplicity/Low overhead Robustness/ Stability Rapid Convergence Flexibility
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Routing on the Internet - the Routing on the Internet - the Two ParadigmsTwo Paradigms
Centralized approach good routes can be found but reliability is
questionable too much traffic on lines connected to the
network center Distributed approach
the failure of one part doesn’t affect the functioning of the rest of the network
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Distributed Approach WinsDistributed Approach Wins
GGP - Predecessor of RIP No distinction between hosts and
routers Attempts to keep track of the load
in the network
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Internet GrowsInternet Grows
Autonomous systems are introduced to support hierarchical routing
The distance vector protocols are not any more sutable
Link state protocols are developed Routers routs
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Host Released from Burden Host Released from Burden of Routingof Routing
The subnet masked bits of the destination address mach those of the local address true - the destination is on the local network
(next hop’s address is the destination address)
false - the destination is remote (next hop’s address is some of the routers)
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Distance Vector Protocols Distance Vector Protocols
Neighboring nodes send information in regular time intervals
Install routes directly in tables, lowest cost wins
The information sent (the distance vectors) are all routes from the table
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The Routing AlgorithmThe Routing Algorithm
the shortest path tree is contained in the routing table
Calculations are based on the Bellman-Ford algorithm
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The Centralized Version of the The Centralized Version of the AlgorithmAlgorithm
Cycle Node B C D E
Initial (., ) (., ) (., ) (., )
1 (1, 1) (2, 2) (3, 1) (4, 2)
A B C
D E
2
3 45
6
1 A B C
D E
2
3 4
1
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The Distributed VersionThe Distributed Version
A B C
D E
1 2
3 45
6
Example of simple network with 5 nodes (routers) and 6 links (interfaces)The cost of all links is assumed to be 1
From A to Link Cost B 1 1 C 1 2 D 3 1 E 1 2
Routing table for A
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AdvantagesAdvantages
simple to implement
low requirement in processing and memory at the nodes
suitable for small networks
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DisadvantagesDisadvantages
Slow convergence Bouncing effect Counting to infinity problem
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Slow Convergence
A B C
D E
2
3 45
6
XXX
When a link breaks the routers are supposed to reestablish the routing tables
link 1 breaks
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The Bouncing Effect
link 2 breaks and A sends its routing table to B before B sends it to A
A B C
D E
3 45
6
XXX1
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Counting to Infinity Problems
D E
3
A B C2
45
XXX
XXX
Links 1 and 6break.
A sends its old routing table before D sends the new routing table
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Split Horizon for Preventing Two-hop Loops
Simple the information about destination routed on
the link is omitted With poisonous reverse
the corresponding distance is set to infinity if the destination is routed on the link
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Triggered UpdatesTriggered Updates
A timer is associated with each entry in the routing table much longer than the period of transmission
of information Triggered updates
request nodes to send messages as soon as they notice a change in the routing table
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Different Distance Vector Different Distance Vector ProtocolsProtocols
Metric they use
Structure of the addresses
Range of links they support
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RIP - Routing Information RIP - Routing Information ProtocolProtocol
first used in XNS (Xerox Network Systems) designed as a component of the networking
code for the BSD release of UNIX incorporated in program “routed” (rote management
daemon)
documented in rfc 1058
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RIP - CharacteristicsRIP - Characteristics
the metric is a hop-count The value of 1 to 15 is used (16 denotes infinity)
supports point-to-point links and broadcast networks
doesn't support CIDR
used only in IP networks at first the intention was to be used in variety of
networks
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RIP - CharacteristicsRIP - Characteristics packets are sent every 30 seconds
or faster when necessary route is considered down if not
refreshed within 180 sec. (distance set to infinity)
two kinds of messages request response
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RIP - Message FormatRIP - Message Format
command (1) version (1) must be zero(2)
address family identifier (2) must be zero(2)
IP address(4)
must be zero(4)
must be zero(4)
metric(4)
0 31
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RIP - ProcessingRIP - Processing
When processing an incoming response a set of validation checks are performed
if each address is valid A, B or C address the network number is not 127 (loopback) or 0
(except in in the case of default address 0.0.0.0) the host part is not a “broadcast address” the metric is not larger than 16 (infinity)
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RIP - ProcessingRIP - Processing
the metric associated with the destination
the address of the “next router” a “recently updated” flag several timers
Each entry in the routing tables contains:
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RIP - LimitationsRIP - Limitations
Maximum hop count of 15 restricts the use of RIP in larger networks, but
prevents the count to infinity problem (endless loops)
Difference in links speed is not reflected in the hop-count metrics congested links can be still included in the best
path
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RIP2 - Why Was Developed?RIP2 - Why Was Developed?
many superior IGP exists (RIP is often referred as Rest In Peace)
there are still many implementations of RIP
given that RIP will still be used, it deserves improvements
RIP 2 is documented in RFC-1287, RFC-1388 and RFC-1389
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RIP2 - Message FormatRIP2 - Message Format
command (1) version (1) Routing domain(2)
address family identifier (2) Route Tag(2)
IP address(4)
Next Hop(4)
Subnet Mask(4)
metric(4)
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RIP2 - The Added FieldsRIP2 - The Added Fields
routing domain used together with the next hop field
to allow multiple autonomous systems to share a single wire
route tag to flag external routes and is for use
by EGP and BGP
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RIP2 - ImprovementsRIP2 - Improvements
authentication routing per subnet support of multiple metrics routing domains multicasting
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AuthenticationAuthentication
specifies that first entry in a packet can be replaced by an “authentication segment”
currently the only algorithm defined is simple “password procedure”
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Routing per SubnetRouting per Subnet
support CIDR
subnet mask included in the message
compatible with RIP1 because the subnet filed is ignored when cooperating with RIP1
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Multiple MetricsMultiple Metrics
metric contains two components hop count throughput, measured as 10logC
ten times the decimal logarithm of the maximum data rate in Kbs
selected path with largest throughput if two paths with same throughput the one
with lower hop count is chosen
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Routing DomainRouting Domain
different autonomous systems share the same wire (Ethernet or FDDI) routers don’t want to process messages
bound to “his” network “routing domain” number is the
autonomous system number
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To create a routing process for RIP, use the configuration command:
router rip
no router rip
To shut down the routing process use the command:
RIP - ConfigurationRIP - Configuration
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Specifying the List of Specifying the List of NetworksNetworks
Specify the list of networks with the network router Specify the list of networks with the network router configuration subcommand.configuration subcommand.
network network-numbernetwork network-number no network network-numberno network network-number
The argument network-number is a network number in dotted IP The argument network-number is a network number in dotted IP notation (of directly connected networks). Note that this number notation (of directly connected networks). Note that this number must not contain subnet information. You may specify multiple must not contain subnet information. You may specify multiple network subcommands. RIP routing updates will be sent and network subcommands. RIP routing updates will be sent and received only through interfaces on this network. The network received only through interfaces on this network. The network router subcommand is a mandatory configuration command and router subcommand is a mandatory configuration command and must be included in the configuration of each IP routing process.must be included in the configuration of each IP routing process.
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Example:
The following example configuration defines RIP as the routing protocol to be used on all interfaces connected to networks 128.99.0.0 and 192.31.7.0.
router ripnetwork 128.99.0.0network 192.31.7.0
To remove a network from the list, use the no network router subcommand followed by the network address.
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RIP is not alone RIP is not alone IGRPIGRP
Developed in the mid1980s by cisco Systems, Inc.
Designed to overcome the limitations of RIP
Initially worked in IP environment, but latter ported to OSI CLNP networks
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IGRP - Main CharacteristicsIGRP - Main Characteristics
Distance vector protocol Uses a combination of metrics
internetwork, delay, bandwidth, reliability and load
the weighting factors are set either by administrators or default values are used
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IGRP - Additional flexibilityIGRP - Additional flexibility
Wide metric ranges allow satisfactory metric setting in
internetworks with widely varying performance characteristics
Permits multipath routing dual equal-bandwidth lines may run a
single stream of traffic in round-robin fashion
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IGRP - Stability FeaturesIGRP - Stability Features hold-downs split horizons poison reverse updates timers
update timer hold time period invalid timer flush timer