rip, igrp, & eigrp characteristics and design. 2 chapter topics ripv1 ripv2 igrp eigrp
TRANSCRIPT
RIP, IGRP, & EIGRPCharacteristics and Design
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Chapter Topics
RIPv1 RIPv2 IGRP EIGRP
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RIPv1
RFC 1058 distance-vector routing protocol uses router hop count as the metric classful routing protocol
does not support VLSM or CIDR no method for authenticating route
updates
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RIPv1
Sends a copy of its routing table to its neighbors every 30 seconds
Uses split horizon with poison reverse
Based on the popular routed program used in UNIX systems since the 1980’s
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RIPv1
Cisco implementation of RIP adds support for load balancing will load-balance traffic if there are
several paths with the same metric Cisco RIP sends triggered updates Administrative distance of 120
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RIPv1
Summarizes to IP network values at network boundaries Network boundary occurs at a router
that has one or more interfaces that do not participate in the specified IP network
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RIPv1 Forwarding Information Base RIPv1 protocol keeps the following
information about each destination: IP address
IP address of the destination host or network Gateway
The first gateway along the path to the destination
Interface The physical network that must be used to
reach the destination Metric
A number indicating the number of hops to the destination
Timer The amount of time since the entry was last
updated
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RIPv1 Forwarding Information Base
Database is updated with the route updates received from neighboring routers
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RIPv1 Message Format
RIP messages are encapsulated using UDP port 520
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RIPv1 Message Format Command
Describes the purpose of the packet. The RFC describes five commands, two of which are obsolete and one of which is reserved. The two used commands are
request Requests all or part of the responding
router's routing table. response
Contains all or part of the sender's routing table. This message might be a response to a request, or it might be an update message generated by the sender
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RIPv1 Message Format
Version Set to the value of 1 for RIPv1.
Address Family Identifier (AFI) Set to a value of 2 for IP.
IP address The destination route. It might be a
network address, subnet, or host route. Special route 0.0.0.0 is used for the default route.
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RIPv1 Message Format
Metric A field that is 32 bits in length. It
contains a value between 1 and 15 inclusive, specifying the current metric for the destination. The metric is set to 16 to indicate that a destination is not reachable.
Because RIP has a maximum hop count, it implements counting to infinity
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RIPv1 Message Format In the RIP message that there are
no subnet masks accompanying each route
Five 32-bit words are repeated for each route entry Five 32-bit words equals 20 bytes for
each route entry Up to 25 routes are allowed in each
RIP message The maximum datagram size is
limited to 512 bytes
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RIPv1 Timers Cisco implementation of RIP uses
four timers Update Invalid Flush Holddown
IP sends its full routing table out all configured interfaces
Table is sent periodically as a broadcast (255.255.255.255) to all hosts
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Ripv1 Timers
Update Timer frequency of the periodic broadcasts default is 30 seconds
Invalid Timer The length of time that must elapse
before a router determines that a route has become invalid
Default is 180 seconds
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Ripv1 Timers Flush Timer
Sets the time between a route becoming invalid and its removal from the routing table
Default is 240 seconds Holddown Timer
Cisco implementation Sets the amount of time during which routing
information is suppressed After the metric for a route entry changes, the
router accepts no updates for the route until the holddown timer expires.
Default is 180 seconds
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Ripv1 Timers
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RIPv1 Design
Things to remember does not support VLSM and CIDR RIPv1 requires the same subnet mask for the
entire IP network RIPv1 is limited to 15 hops broadcasts its routing table every 30 seconds usually limited to accessing networks where it
can interoperate with servers running routed or with non-Cisco routers
also appears at the edge of larger networks
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RIPv2
First described in RFC 1388 and RFC 1723 (1994); the current RFC is 2453, (1998)
Need to use VLSM and other requirements prompted the definition of RIPv2
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RIPv2
RIPv2 improves upon RIPv1 with ability to use VLSM support for route authentication, multicasting of route updates
uses the IP address 224.0.0.9 Support of CIDR
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RIPv2
Some features remain the same Updates every 30 seconds Retains the 15-hop limit Uses triggered updates Uses UDP port 520 Retains the loop-prevention strategies
of poison reverse and counting to infinity
Administrative distance of 120 Summarize IP networks at network
boundaries
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RIPv2 Authentication
Prevent communication with any RIP routers that are not intended to be part of the network UNIX stations running routed
RFC 1723 defines simple plain-text authentication
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MD5 Authentication
Cisco implementation provides the ability to use Message Digest 5 (MD5) authentication RFC 1321
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RIPv2 Forwarding Information Base
Maintains the same routing table database as in Version 1 Difference is that it also keeps the
subnet mask information IP Address Gateway Interface Metric Timer
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RIPv2 Message Format
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RIPv2 Message Format
Takes advantage of the unused fields in the RIPv1 message format Adding subnet masks and other
information
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RIPv2 Message Format Description of each field
Command Indicates whether the packet is a request or a
response message Version
Specifies the RIP version used AFI
Specifies the address family used Set to a value of 2 for IP
Route tag Provides a method for distinguishing between
internal routes (learned by RIP) and external routes (learned from other protocols)
Optional Tag
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RIPv2 Message Format
IP address IP address (network) of the destination
Subnet mask Subnet mask for the destination
Next hop Indicates the IP address of the next hop
where packets are sent to reach the destination.
Metric Indicates how many router hops to reach
the destination
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RIPv2 Timers
Same as RIPv1 Update – 30 s Invalid – 180 s Holddown – 180 s Flush – 240 s
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RIPv2 Design Things to remember
Supports VLSM within networks and CIDR for network summarization
Summarization of routes in a hierarchical network
Limited to 16 hops Multicasts its routing table every 30 seconds Usually limited to accessing networks where it
can interoperate with servers running routed or with non-Cisco router
Appears at the edge of larger internetworks
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IGRP
Developed by Cisco to overcome the limitations of RIPv1
Distance-vector routing protocol Composite metric
Uses bandwidth and delay as parameters instead of hop count
Can also use reliability and load Not limited to the 15-hop limit of RIP
Default is 100 hops – configurable up to 255
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IGRP
Routers usually select paths with a larger minimum-link bandwidth over paths with a smaller hop count Links do not have a hop count They are exactly one hop
Classful protocol cannot implement VLSM or CIDR
Summarizes at network boundaries
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IGRP
Loop avoidance Split horizon with poison reverse Triggered updates Holddown timers
Can load balance over unequal-cost links
Cisco Proprietary
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IGRP Timers
Update Timer 90 seconds
Invalid Timer 270 seconds
Holddown Timer 280 seconds
Flush Timer 630 seconds
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IGRP Metrics
IGRP uses a composite metric based on bandwidth, delay, load, and reliability Default is bandwidth and delay
Formula for calculation
IGRPmetric = {k1 x BW + [(k2 x BW)/(256 – load)] + k3 x delay} x {k5/(reliability + k4)}
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IGRP Metrics
By default, k1 and k3 are set to 1, and k2, k4, and k5 are set to 0
Change the default metrics using the metric weight tos k1 k2 k3 k4 k5 subcommand under router igrp tos is always 0 to use all metrics:
Router(config)#router igrp 10
Router(config-router)#metric weight 0 1 1 1 1 1
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IGRP Design
Things to remember does not support VLSM does not support CIDR and network
summarization within the major network boundary
network diameter can be larger than that of networks using RIP
broadcasts its routing table every 90 seconds
limited to Cisco-only networks
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IGRP Design
Starting with IOS version 12.3, IGRP is NO LONGER SUPPORTED Must migrate to EIGRP or to another
protocol
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EIGRP
Released in the early 1990s as an evolution of IGRP
classless protocol Permits the use of VLSM Supports CIDR
does not send routing updates periodically
authentication with simple passwords or with MD5
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EIGRP
Autosummarizes networks at network borders
Can load-balance over unequal–cost paths
Uses IP protocol 88 Cisco Proprietary
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EIGRP An “advanced distance-vector”
protocol Advertises its routing table to its
neighbors Uses hellos and forms neighbor
relationships Sends partial updates when a metric or
the topology changes does not send full routing-table updates in
periodic fashion Uses DUAL to determine loop-free
paths
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EIGRP
Administrative Distances Internal routes have an AD of 90 Summary routes have an AD of 5 External routes (from redistribution)
have an AD of 170
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EIGRP Components
EIGRP has four components that characterize it: Protocol-dependent modules Neighbor discovery and recovery Reliable Transport Protocol (RTP) DUAL
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Protocol-Dependent Modules
Different modules that independently support IP, Internetwork Packet Exchange (IPX), and AppleTalk
The logical interface between DUAL and routing protocols
Module sends and receives packets but passes received information to DUAL, which makes routing decisions.
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Neighbor Discovery and Recovery
multicasts hello packets (224.0.0.10) every 5 seconds for most networks
router builds a table with EIGRP neighbor information
holdtime to maintain a neighbor is three times the hello time: 15 seconds
multicasts hellos every 60 seconds on multipoint WAN interfaces (X.25, Frame Relay, ATM) with speeds less than 1544 Mbps Holdtime is now 180 seconds
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RTP
ensures the reliable delivery of route updates
uses sequence numbers to ensure ordered delivery
sends update packets using multicast address 224.0.0.10
acknowledges updates using unicast hello packets with no data
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DUAL
Implemented to select paths and guarantee freedom from routing loops Mathematically proven to result in a
loop-free topology No need for periodic updates or route-
holddown mechanisms
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DUAL
Selects a best path and a second best path to reach a destination Best path is the successor Second best path (if available) is the
feasible successor Feasible distance is the lowest
calculated metric of a path to reach the destination
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DUAL
Passive state when the router is not performing any
recomputations for an entry
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DUAL
Active State successor goes down and there are no
feasible successors routers send query packets to
neighboring routers Neighbor can send a reply packet
It has a feasible successor Neighbor can send a query packet
Does not have a feasible successor Route does not return to passive state
until it has received a reply packet from each neighboring router
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EIGRP Timers Sends updates only when necessary
Sends them only to neighboring routers There is no periodic update timer On high-speed networks, the default hello
packet interval is 5 seconds multipoint networks with link speeds of T1 and
slower, hello packets are unicast every 60 seconds
Holdtime to maintain a neighbor adjacency is three times the hello time 15 seconds or 180 seconds
Updates are sent to the multicast address 224.0.0.10 (all EIGRP routers)
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EIGRP Metrics
Uses the same composite metric as IGRP BW term is multiplied by 256 for finer
granularity Metric is based on bandwidth, delay,
load, and reliability MTU is not an attribute
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EIGRP Packet Types
EIGRP uses five packet types: Hello
Discovery of neighbors. They are multicast to 224.0.0.10
Acknowledgment Acknowledges the reception of an update packet It is a hello packet with no data. Sent to the unicast address of the sender of the
update packet Update
Update packets contain routing information for destinations.
Unicasts update packets to newly discovered neighbors
Multicasts update packets to 224.0.0.10 when a link or metric changes. Update packets are acknowledged to ensure reliable transmission.
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EIGRP Packet Types
Query sent to find feasible successors to a
destination Always multicast.
Reply Sent to respond to query packets. Provide a feasible successor to the sender
of the query Packets are unicast to the sender of the
query packet.
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EIGRP Design
Things to remember Supports VLSM, CIDR, and network
summarization Not limited to 16 hops as RIP is Does not broadcasts its routing table
periodically No large network overhead
Use EIGRP for large networks Potential routing protocol for the core
of a large network Provides for route authentication
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Summary