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52 Cards in this Set

  • Front
  • Back

EIGRP

Enhanced Interior Gateway Routing Protocol

Advertised Distance

is an arbitrary numerical value assigned to a routing protocol, a static route or a directly-connected route based on its perceived quality of routing.

How is EIGRP Calculated

1. Bandwidth


2. Delay


3. Load


4. Reliability

Feasible distance (FD)

the metric of the best route to reach a network. That route will be listed in the routing table.

Reported distance (RD)

the metric advertised by a neighboring router for a specific route. It other words, it is the metric of the route used by the neighboring router to reach the network.

Successor

is the route with the best metric (Best Path) to reach a destination. That route is stored in the routing table.

A feasible successor

is a backup path to reach that same destination that can be used immediately if the successor route fails.

Variance Command

The variance is a multiplier. So what ever the metric is for your successor you multiply that by the variance and what ever feasible successors fall into that range will be used for load balancing.

Neighbor Discovery/Recovery


Neighbor Discovery/Recovery is the process that routers use to dynamically learn of other routers on their directly attached networks

Adjacency

A neighbor relationship

RTP

Reliable Transport Protocol



provides sequencing and acknowledgment for EIGRP packets between neighbors.

multi-access network

A flexible system by which every station can have access to the network at all times; provisions are made for times when two computers decide to transmit at the same time.


http://www.commodore.ca/manuals/128_system_guide/glossary.htm

Hello Packets

are used for neighbor discovery. As soon as you send hello packets and receive them your EIGRP routers will try to form the neighbor adjacency.

Query

Packets have routing information and are sent reliable to whatever router that requires the information. Update packets can be sent to a single neighbor using unicast or to a group of neighbors using multi-cast

Reply

Packets are used in response to the query packets and are reliable

ACK packets

are used to acknowledge the receipt of update, query and replay packets. Ack packets are sent by using unicast

Neighbor Table

This is where EIGRP stores all information of directly connected neighbors.

EIGRP Topology Table

this is the information routers exchange after routers have become neighbors

The command to start eigrp using AS (autonomous system) number 1

router eigrp 1

Why is "no auto summary" needed?

by default EIGRP will behave like a classful routing protocol which means it won't advertise the subnet mask along the routing information.

Passive Interface Command

Advertise a network without sending EIGRP packets on the interface and forming EIGRP neighbors

passive-interface default

If you have a configuration with 50+ interfaces you probably don't want to type this command on each of those interfaces. You can configure passive-interface default and only activate the interfaces you want to run EIGRP on

Show ip protocols

it will show you


1. What networks you are routing


2. Passive Interfaces


3. Administrative Distance

H (Handle)

the order when the neighbor adjacency was established. your first neighbor will have a value of 0, the second 1, and so on

Hold Uptime (sec)

this is the holddown timer per EIGRP protocol.



NOTE:


once this timer expires we will drop the neighbor adjacency. The default holddown timer is 15 seconds.



On older IOS versions only a hello packet would reset the holddown timer but on newer IOS versions any EIGRP packet after the first hello will reset the holddown timer.

Holddown Timer

works by having each router start a timer when they first receive information about a network that is unreachable. Until the timer expires, the router will discard any subsequent route messages that indicate the route is in fact reachable.

SRTT

Smooth round-trip time



The number of miliseconds it takes to send an EIGRP packet to you neighbor and receive an acknowledgment packet back

RTO

Retransmission Timeout



The amount of time in miliseconds that EIGRP will wait before retransmitting a packet from the retransmission queue to this neighbor

Q Cnt

Q Count



The number of EIGRP packets (update, Query or Reply) in the queue that are awaiting transmission. Ideally you want this number to be 0 otherwise it might be an indication of congestion on the network.

Seq Num

Sequence Number



This will show you the sequence number of the last update, query or reply packet that you received from your EIGRP neighbor

Passive

Passive is good.



we like routing information to be passive which means that we have learned information about a network and there are no changes in the topology table.

Active

Active is not good.



It means we have lost information about a certain network and EIGRP doesn't know another way of reaching this network. It will go into active mode and send query packets to ALL its neighbors asking them if they know how to reach this network.

Reply Status

EIGRP will track all the query packets it has sent to neighbors since you need a reply in return. By setting the reply status flag it will do this

Sia Status

Stuck in Active



This is bad



It means that EIGRP has not received a reply to q query packet from one of the neighbors within the allowed time (about 3 minutes). When this happens EIGRP will drop neighbor adjacency and it will be stuck in active.

What does the P stand for in



P 2.2.2.0/24

Passive

Feasible Distance

Total Distance

Which number is the feasible distance?



(156160/128256)

156160

Advertised Distance

This is the where your EIGRP neighbor reports how far it is for him to reach the network

Which number is the administrative distance?



(156160/128256)

128256

What is the letter D in the routing table?

Dual or diffusing update algorithm

What is Dual?

This is the algorithm behind EIGRP which is why we find the D listed in the routing table.



NOTE:


We do not use E because that is used for Exterior gateway protocol.

In the statement



2.2.2.0 [90//156160]



What is the feasible distance?

156160

What command do you use to show k values?

Show ip protocols

How can you change the bandwidth Static Value?

Bandwidth Command



NOTE:


this does not change the actual value of the command

When EIGRP has to choose from two routes; will it choose the route with the lower or higher bandwidth?

Lower

Can you use the delay command to change a value influencing EIGRP?

Yes



NOTE:


It does not actually change the delay for the interface but can be used to influence routing protocols

Is MTU used in the metric calculation for EIGRP?

Maximum Transmission Unit



This is being exchanged between EIGRP neighbors but is not used for metric calculation

What is the EIGRP Formula?

Metric = bandwidth (slowest link) + delay (sum of delays)

What is the bandwith calculation?

(10 ^7 / minimum bandwidth in the path) * 256

What is the calculation for delay?

sums of delays in the path multiplied by 256 (in tens of microseconds)

Why do we use 256 when multiplying with EIGRP?

So it is compatible with IGRP

What is the bandwidth for a T1 interface?

1.544 Mbit