IP Routing

Router

A Router is a physical device used to connect two different network (LAN), check their destination in Routing Table and transmit the message to the required LAN

– Work on logical address (IP)– Maintain routing table– Select best path– Layer 3 device– Connect different network– Backbone on internet– Packet filtering– Packet routing

It is denoted by symbol

X

Interface

E0 – Ethernet S0 – Serial Interface 0 S1 – Serial Interface 1

DCE – DATA COMMUNICATION EQUIPMENT(CLOCK RATE)DTE – DATA TERMINAL EQUIPMENT

HOW TO LOGIN IN ROUTER

Start Program Accessories Communication HyperTerminal

Router Modes

User exec mode :-> Router> Privilege exec mode :-> Router# Global Configuration Mode :-> Router(config)# Other Configuration Mode :-> Router(config-if)# Router(config-line)# Router(config-router)# Rx-boot Mode :-> It is used in password recovery. Initial Configuration Mode :-> Setup mode

USER EXEC MODE

IT is represented by router>. Minimal examination of the router. No change will take place.

router>enable

router#

PRIVILAGE EXEC MODE

It is represented by router #. Detail examination of the router &

troubleshooting.

router#config t {t=terminal}

router(config)#

GLOBAL CONFIGURATION MODE

It is represented by router(config)#. Configuration means router programming. Change the router name

router(config)#hostname GIT

GIT(config)#

OTHER CONFIGURATION MODE

It is represented by router(config-if)# router(config-line)# router(config-router)# router(config)#interface ethernet 0 router(config-if)# router(config)#line console 0 router(config-line)#

router(config)#router rip router(config-router)#

INDEX

Static Routing Default Routing Dynamic Routing

– RIP – IGRP– EIGRP– OSPF

IP ROUTING

Static Routing– Static Routing occurs when you manually add

routes in each routers routing table Default Routing

– We use default routing to send packets only one exit path out of the network

Dynamic routing– Dynamic routing is when protocols are used to

find networks.

Static Routing

GIT Family

STATIC ROUTE

A static route is a manually configured route on your router. Static routers are typically used in smaller network.

To configure a static route, use one of the two commands:

Router(config)# Ip route Distination_network Subnet_mask Ip_address_of_next_neighbor

OrRouter(config)# Ip route Distination_network Subnet_mask Interface_to_exit

X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

Router-1

EnableConfig tHostname Router1Int e0

ip address 10.0.0.1 255.0.0.0no shut

Int s0ip address 20.0.0.1 255.0.0.0no shut

clock rate 64000Exit

Ip route 30.0.0.0 255.0.0.0 20.0.0.2

Router-2




ExitIp route 10.0.0.0 255.0.0.0 20.0.0.1

ExitShow ip route

Configure Router 1

from PC1

Set IP Address to PC 1

EnableConfig tHostname rt1

Int e0Ip address 10.0.0.1 255.0.0.0No shut

int s0ip address 20.0.0.1 255.0.0.0no shut

ip route 30.0.0.0 255.0.0.0 20.0.0.1

int s0clock rate 64000

exitexitshow run

copy running-config startup-config (for saving configuration)

CONFIGURE ROUTER-2

AND PC2

SET PC2 IP ADDRESS

enableconfig thostname rt2

int e0ip address 30.0.0.1 255.0.0.0no shut

int s1ip address 20.0.0.2 255.0.0.0no shutdown

int s1ip address 20.0.0.2 255.0.0.0no shutdownexit

ip route 10.0.0.0 255.0.0.0 20.0.0.2exit

show running-config

To check the connectivity from router

ping 10.0.0.1ping 10.0.0.2ping 20.0.0.1ping 20.0.0.2ping 30.0.0.1

Default Routing

Default Routing

– We use default routing to send packets only one exit path out of the network like Router-1 and Router-3. In Router-2 there are two exit path.

IP ROUTE 0.0.0.0 0.0.0.0 20.0.0.1

X X

Router-1 Router-2

X

Router-3

Dynamic Routing

Routing Protocol

There are three types of routing protocol– Distance Vector– Link State– Hybrid

Routing Protocol

Distance vector Protocol – Complete routing table send for route update

Exp – RIP, IGRP

Link State Protocol– Only change (through hello packet) send for route update

Exp - OSPF

Hybrid Protocol– Both feature Distance Vector & Link State

Exp - EIGRP

RIP

ROUTING INFORMATION PROTOCOL

RIP

ROUTING INFORMATION PROTOCOL Distance Vector Routing Protocol Update Routing Table - Every 30 Sec. Max Hop count - 15 Class full

X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

Set IP Address to PC1

Winipcfg

IP Address – 10.0.0.2 Subnet – 255.0.0.0 Gateway – 10.0.0.1


Winipcfg


Router-1




clock rate 64000ExitRouter rip

network 10.0.0.0network 20.0.0.0

Router-2




ExitRouter rip


X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

X40.0.0.2

50.0.0.1

50.0.0.2

Router-3

S1

E0

S0

40.0.0.1


Winipcfg


Router-1




clock rate 64000ExitRouter rip


Router-2




Int s0ip address 40.0.0.1 255.0.0.0no shutclock rate 64000

ExitRouter rip

network 20.0.0.0network 30.0.0.0network 40.0.0.0

Router-3




ExitRouter rip


Comparison

RIP V 1 Distance Vector Max Hop count 15 Class full No support for VLSM No support for

Discontinuous Network

RIP V 2 Distance Vector Max Hop count 15 Classless Support for VLSM Support for

Discontinuous Network

Router-3




ExitRouter rip

network 40.0.0.0network 50.0.0.0version 2

Administrative Distance

The administrative distance (AD) is used to rate the trust worthiness of routing information received on a router from neighbor router.

Administrative distance is an integer from 0 to 255. If router receives two updates the first thing the

router check is the AD. Lower AD will be placed in the routing table.

If the both router same AD then routing protocol check Hop count or bandwidth of line.

Default Administrative Distance

Route Source Connected interface Static Route EIGRP IGRP OSPF RIP EXTERNAL EIGRP Unknown

Default AD. 0 1 90 100 110 120 170 255 (Route never used)

Autonomous System Number (AS)

All routers Share routing table information. in the same AS Number

Autonomous System Number10

Autonomous System Number20

IGRP (Interior Gateway Routing Protocol)

IGRP is Cisco-Proprietary Distance vector routing protocol means this protocol is work only on Cisco routers.

Use Autonomous System Number Maximum Hop Count – 255 (Default 100) Metric

– Bandwidth and Delay

Diffrences

IGRP Can be used in large

internetworks Uses an autonomous

system number for activation

Gives a full route table update every 90 seconds

Has an administrative distance of 100

Uses Bandwidth and delay of the line as metric

maximum hop count of 255

RIP Works best in smaller

networks Does not use autonomous

system number Gives full route table update

every 30 seconds Has an administrative

distance of 120 Uses only hop count to

determine the best path to a remote network

15 hops maximum.

X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

Router-1

EnableConfig t

Hostname Router1


Int s0I p address 20.0.0.1 255.0.0.0

No shut

Clock rate 64000

Router IGRP 10Network 10.0.0.0Network 20.0.0.0

Router-2

EnableConfig t

Hostname Router2


Int s1 Ip address 20.0.0.2 255.0.0.0

No shut

Router IGRP 10Network 20.0.0.0Network 30.0.0.0


Winipcfg


Trace the route for 10.0.0.10Which is through router-2

In router-2 close the link s0using shut command

Router-2 close the link s0Request is not routing After few second Router-4 Search the new Route through Router-3

Enhance Interior Gateway Routing Protocol

EIGRP

EIGRP

It is HYBRIDE routing protocol.( D.V + L.S) Support for IP, IPX and AppleTalk via protocol

dependent modules. Support for VLSM/CIDR. Support for summaries and discontiguous networks. Efficient neighbor discovery Communication via Reliable Transport Protocol

(RTP) Best path selection via Diffusing Update Algorithm

(DUAL)

EIGRP

Protocol Dependent Modules– Maintain a separate series of tables means there

is IP/EIGRP tables, IPX/EIGRP tables and AppleTalk/EIGRP tables.

Neighbor Discovery Hello or Acknowledgement Received AS Number Match Identical Metric's

Discovering Routes

I am Router A, Who Is on the Link?

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Hello11

AA BB

Discovering Routes

Update


Here Is My Routing Information (Unicast)



Hello11

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Discovering Routes

Thanks for the Information!Ack


Update





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Topology Table

Topology Table

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Update





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Here Is My Route Information (Unicast)Update




Update





Discovering Routes

Hello

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Topology Table

Topology Table

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Converged

Thanks for the Information! Ack


Discovering Routes

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Topology Table

Topology Table

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Hello

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Reliable Transport Protocol (RTP)

Reliability is the key concern, a mechanism that using multicast and unicast for track the neighbor (who have replied).

Class D address 224-240. Neighbor is declared dead if doesn't get reply

in 16 unicast attempts.

Diffusing Update Algorithm (DUAL)

DUAL is responsible for selecting and maintaining information about the best paths.

First, EIGRP routers maintain a copy of all of their neighbors routers in neighbors table, if the best path goes down, it is simple, examining the contents of the topology table to select the best replacement route.

Secondly, if there is not a good alternative in the local topology table, EIGRP routers very quickly ask their neighbors for help to find one best route.

The whole idea of the Hello protocol is to enable the rapid detection of new or dead neighbors.

D EIGRP Topology(a) Cost (2) (fd)

via B Cost (2/1) (Successor)via C Cost (5/3)



E EIGRP Topology (a) Cost (3) (fd)

via D Cost (3/2) (Successor)via C Cost (4/3)



C EIGRP Topology(a) Cost (3) (fd)

via B Cost (3/1) (Successor)via D Cost (4/2) (fs)via E Cost (4/3)



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via E (q)via C Cost (5/3) (q)








via B Cost (3/1) (Successor)via Dvia E Cost (4/3)



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Support Large Networks

EIGRP includes a bunch of cool features that make it suitable for use in large networks

– Support for multiple ASes on a single router– Support for VLSM and summarization– Route discovery and maintenance

Multiple ASes

EIGRP uses Autonomous System Number to identify the collection of routers that share route information,

Well it is possible to divide the large network into multiple distinct EIGRP autonomous systems or ASes.

Route information can be shared among the Different ASes via redistribution.

VLSM Support and Summarization

One of the classless routing protocols support VLSM.

Use of discrete subnets, gives lot more flexibility.

What is discrete network? It is one that has two or more subnet works for a

classful network connected together by different classful networks.

– RIPV2 and EIGRP Support Discrete networking, but not by default. OSPF does support discrete networking by default.

Route Discovery and Maintenance

EIGRP Supports the concept of neighbors that are discovered via a Hello Process and uses the routing by rumor mechanism (a route is update when hear about route from another routers ).

Maintain three types of table Routing Table – Active Roots

Neighbor Table – Information about adjacent neighbors.

Topology Table – All the roots are stored in it.

Metrics

Select best possible path, use a combination of four– Bandwidth– Delay– Load– Reliability

X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

Router-1

EnableConfig t

Hostname Router1


Int s0Ip address 20.0.0.1 255.0.0.0No shut

Clock rate 64000

Router EIGRP 100Network 10.0.0.0Network 20.0.0.0

Router-2

EnableConfig t

Hostname Router2


Int s1Ip address 20.0.0.2 255.0.0.0No shut

Router EIGRP 100Network 20.0.0.0Network 30.0.0.0

OSPF

Open Shortest Path First

OSPF

OSPF is the first link state routing protocol OSPF provides the following feature

– Consists of area and autonomous system– Share routing information through link state advertisement

(LSA)– LSA contain small bit of information about route– Minimizes routing update traffic– Supports VLSM/CIDR– Has unlimited hop counts– Allow multi-vendor deployment (Open Standard)

X

X

X

X

X

Area 0

Area 1Area 2

Back Bone AreaBack Bone Area Router

Internal Router

Area Boarder Router

Back Bone Area – Area 0 is a backbone area

Back Bone Router – Router exist in back bone area.

Internal Router – all interface in one area

Area Boarder Router – one interface in one area other interface in other

area

Shortest Path First (SPF)

Within an area each router calculate the best shortest path . This calculation is based upon the information collected in the topology database and the algorithm called shortest path first (SPF).

(Each router in an area constructing a tree much like a family tree- where the router is the root, and all other network arranged along the branches and leaves.)

Enabling OSPF

Router(config)# router ospf ?

(1 - 65535) A value in the range 1 to 65535 identifies the OSPF Process ID

You can have more than one ospf process (running simultaneously) on the same router if you want. The second process will maintain an entirely separate copy of its topology table and manage its communication independently of the first process.

Configuring OSPF Areas

Router(Config)# router ospf 1Router(config-router)# network 10.0.0.0 0.255.255.255 area 1

A quick review of wildcard0 – indicates that corresponding value (10) in the network must match

exactly.255 – indicates (any) that you don't case what the corresponding value

is in the network.

Remember – OSPF routers will only become neighbor if their interfaces share a network that is configured to belong to the same area number.

X X

10.0.0.2

10.0.0.1

20.0.0.1 20.0.0.2

30.0.0.1

30.0.0.2

Router-1 Router-2

S0

E0

S1

E0

X40.0.0.2

50.0.0.1

50.0.0.2

Router-3

S1

E0

S0

40.0.0.1

Router-1





Router ospf 5network 10.0.0.0 255.0.0.255 area 1

Router-2






Router ospf 5network 20.0.0.0 255.0.0.255 area 1

Router-3




ExitRouter ospf 5

network 40.0.0.0 255.0.0.255 area 1

Routing Loops

Solution for Routing loops– Maximum Hop Count

The routing loop problem just described is called counting to infinity, and it is caused by broadcasts wrong information throughout the internetwork.

– Split Horizon Routing protocol observe which interface a network route was

learned. It would not accept the route back to other interface.– Route Poisoning

Another way to avoid problems caused by inconsistent updates start and stop network.

– Hold downs A hold down prevents regular update messages from

reinstating a route that is going up and down (called flapping).

Note that RTE has recognized that 203.250.15.0 has two subnets while RTA thinks that it has only one subnet (the one configured on the interface). Information about subnet 203.250.15.0 255.255.255.252 is lost in the RIP domain. In order to reach that subnet, a static route needs to be configured on RTA:

OSPF versus RIP

The rapid growth and expansion of today's networks has pushed RIP to its limits. RIP has certain limitations that could cause problems in large networks:

RIP has a limit of 15 hops. A RIP network that spans more than 15 hops (15 routers) is considered unreachable.

RIP cannot handle Variable Length Subnet Masks (VLSM). Given the shortage of IP addresses and the flexibility VLSM gives in the efficient assignment of IP addresses, this is considered a major flaw.

Periodic broadcasts of the full routing table will consume a large amount of bandwidth. This is a major problem with large networks especially on slow links and WAN clouds.

RIP converges slower than OSPF. In large networks convergence gets to be in the order of minutes. RIP routers will go through a period of a hold-down and garbage collection and will slowly time-out information that has not been received recently. This is inappropriate in large environments and could cause routing inconsistencies.

RIP has no concept of network delays and link costs. Routing decisions are based on hop counts. The path with the lowest hop count to the destination is always preferred even if the longer path has a better aggregate link bandwidth and slower delays.

RIP networks are flat networks. There is no concept of areas or boundaries. With the introduction of classless routing and the intelligent use of aggregation and summarization, RIP networks seem to have fallen behind.

Some enhancements were introduced in a new version of RIP called RIP2. RIP2 addresses the issues of VLSM, authentication, and multicast routing updates. RIP2 is not a big improvement over RIP (now called RIP 1) because it still has the limitations of hop counts and slow convergence which are essential in todays large networks.

OSPF versus RIP

OSPF, on the other hand, addresses most of the issues presented above: With OSPF, there is no limitation on the hop count. The intelligent use of VLSM is very useful in IP address allocation. OSPF uses IP multicast to send link-state updates. This ensures less processing on routers that

are not listening to OSPF packets. Also, updates are only sent in case routing changes occur instead of periodically. This ensures a better use of bandwidth.

OSPF has better convergence than RIP. This is because routing changes are propagated instantaneously and not periodically.

OSPF allows for better load balancing. OSPF allows for a logical definition of networks where routers can be divided into areas. This will

limit the explosion of link state updates over the whole network. This also provides a mechanism for aggregating routes and cutting down on the unnecessary propagation of subnet information.

OSPF allows for routing authentication by using different methods of password authentication. OSPF allows for the transfer and tagging of external routes injected into an Autonomous System.

This keeps track of external routes injected by exterior protocols such as BGP. This of course would lead to more complexity in configuring and troubleshooting OSPF networks.

Administrators that are used to the simplicity of RIP will be challenged with the amount of new information they have to learn in order to keep up with OSPF networks. Also, this will introduce more overhead in memory allocation and CPU utilization. Some of the routers running RIP might have to be upgraded in order to handle the overhead caused by OSPF.

OSPF

What Do We Mean by Link-States? OSPF is a link-state protocol. We could think of a link as being an interface on the router. The state of the link is

a description of that interface and of its relationship to its neighboring routers. A description of the interface would include, for example, the IP address of the interface, the mask, the type of network it is connected to, the routers connected to that network and so on. The collection of all these link-states would form a link-state database.

Link-State Algorithm OSPF uses a link-state algorithm in order to build and calculate the shortest path to all known destinations. The

algorithm by itself is quite complicated. The following is a very high level, simplified way of looking at the various steps of the algorithm:

Upon initialization or due to any change in routing information, a router will generate a link-state advertisement. This advertisement will represent the collection of all link-states on that router.

All routers will exchange link-states by means of flooding. Each router that receives a link-state update should store a copy in its link-state database and then propagate the update to other routers.

After the database of each router is completed, the router will calculate a Shortest Path Tree to all destinations. The router uses the Dijkstra algorithm to calculate the shortest path tree. The destinations, the associated cost and the next hop to reach those destinations will form the IP routing table.

In case no changes in the OSPF network occur, such as cost of a link or a network being added or deleted, OSPF should be very quiet. Any changes that occur are communicated via link-state packets, and the Dijkstra algorithm is recalculated to find the shortest path.

Shortest Path Algorithm The shortest path is calculated using the Dijkstra algorithm. The algorithm places each router at the root of a

tree and calculates the shortest path to each destination based on the cumulative cost required to reach that destination. Each router will have its own view of the topology even though all the routers will build a shortest path tree using the same link-state database. The following sections indicate what is involved in building a shortest path tree.

Neighbors

Routers that share a common segment become neighbors on that segment. Neighbors are elected via the Hello protocol. Hello packets are sent periodically out of each interface using IP multicast (Appendix B). Routers become neighbors as soon as they see themselves listed in the neighbor's Hello packet. This way, a two way communication is guaranteed. Neighbor negotiation applies to the primary address only. Secondary addresses can be configured on an interface with a restriction that they have to belong to the same area as the primary address.

Two routers will not become neighbors unless they agree on the following: Area-id: Two routers having a common segment; their interfaces have to belong to the same area on that

segment. Of course, the interfaces should belong to the same subnet and have a similar mask. Authentication: OSPF allows for the configuration of a password for a specific area. Routers that want to

become neighbors have to exchange the same password on a particular segment. Hello and Dead Intervals: OSPF exchanges Hello packets on each segment. This is a form of keepalive

used by routers in order to acknowledge their existence on a segment and in order to elect a designated router (DR) on multiaccess segments.The Hello interval specifies the length of time, in seconds, between the hello packets that a router sends on an OSPF interface. The dead interval is the number of seconds that a router's Hello packets have not been seen before its neighbors declare the OSPF router down.

OSPF requires these intervals to be exactly the same between two neighbors. If any of these intervals are different, these routers will not become neighbors on a particular segment. The router interface commands used to set these timers are: ip ospf hello-interval seconds and ip ospf dead-interval seconds .

Stub area flag: Two routers have to also agree on the stub area flag in the Hello packets in order to become neighbors. Stub areas will be discussed in a later section. Keep in mind for now that defining stub areas will affect the neighbor election process.

VLSM

Another issue to consider is VLSM (Variable Length Subnet Guide)(Appendix C). OSPF can carry multiple subnet information for the same major net, but other protocols such as RIP and IGRP (EIGRP is OK with VLSM) cannot. If the same major net crosses the boundaries of an OSPF and RIP domain, VLSM information redistributed into RIP or IGRP will be lost and static routes will have to be configured in the RIP or IGRP domains. The following example illustrates this problem:

In the above diagram, RTE is running OSPF and RTA is running RIP. RTC is doing the redistribution between the two protocols.

The problem is that the class C network 203.250.15.0 is variably subnetted, it has two different masks 255.255.255.252 and 255.255.255.192. Let us look at the configuration and the routing tables of RTE and RTA:

RTA# interface Ethernet0 ip address 203.250.15.68 255.255.255.192 router rip network 203.250.15.0 RTC# interface Ethernet0 ip address 203.250.15.67 255.255.255.192 interface Serial1 ip address 203.250.15.1 255.255.255.252 router ospf 10 redistribute rip metric 10 subnets network 203.250.15.0 0.0.0.255 area 0 router rip redistribute ospf 10 metric 2 network 203.250.15.0 RTE#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is not set 203.250.15.0 is variably subnetted, 2 subnets, 2 masks C 203.250.15.0 255.255.255.252 is directly connected, Serial0 O 203.250.15.64 255.255.255.192 [110/74] via 203.250.15.1, 00:15:55, Serial0 RTA#show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is not set 203.250.15.0 255.255.255.192 is subnetted, 1 subnets C 203.250.15.64 is directly connected, Ethernet0

Note that RTE has recognized that 203.250.15.0 has two subnets while RTA thinks that it has only one subnet (the one configured on the interface). Information about subnet 203.250.15.0 255.255.255.252 is lost in the RIP domain. In order to reach that subnet, a static route needs to be configured on RTA:

RTA# interface Ethernet0 ip address 203.250.15.68 255.255.255.192 router rip network 203.250.15.0 ip route 203.250.15.0 255.255.255.0 203.250.15.67

This way RTA will be able to reach the other subnets.

Converged

Thanks for the Information! Ack


Discovering Routes

66

Topology Table

Topology Table

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EIGRP Reliable Transport Protocol

EIGRP reliable packets are packets that requires explicit acknowledgement:– Update– Query– Reply

EIGRP unreliable packets are packets that do not require explicit acknowledgement:– Hello– Ack

EIGRP Reliable Transport Protocol

The router keeps a neighbor list and a retransmission list for every neighbor

Each reliable packet (Update, Query, Reply) will be retransmitted when packet is not acked

EIGRP transport has window size of one (stop and wait mechanism)– Every single reliable packet needs to be

acknowledged before the next sequenced packet can be sent

IP Routing

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