IT-341 Quiz 5: Comprehensive Review on Classless Routing and Static Routing Concepts

Types of static routes

Standard

Default

Floating

Summary

Next-hop route

Only the next hop IP address is specified

Directly connected static route

Only the router exit interface is specified

Fully specified static route

The next-hop IP address and exit interface are specified.

IP, Sub, IP, exit int

Static Route Command

(config)# ip route nextwork address, subnet address, exit interface, ip address of next hop

Ways to verify a static route

Show IP route static

Show IP route network

Show running-config

Default Static route

A route that matches all packets, also known as a route of last resort, represents any network that is not on a routing table.

Commonly used when connecting an edge router to a service provider network or a stub router

Stub router

a router with only one upstream neighbor router.

Default route configuration

0.0.0.0 0.0.0.0 (ip address | exit interface)

Floating static routes

provide backup to a primary static or dynamic route, only used when the primary route is not available

-configured with a higher administrative distance than the primary route

Administrative distance

The trustworthiness of a route. If multiple paths to a destination exists the router will choose the path with the lowest administrative distance.

Default administrative distance

static routes have a default administrative distance of 1, making them preferable to dynamic routing protocols. The administrative distance can be increased to make the route less desirable, in this route the static route floats and is not used when the route with better administrative distance is active.

Configure floating routes

ip route 0.0.0.0 0.0.0.0 IP administrative distance

test the floating static route

# show ip route static

C

Connected route

L

Local routes

Static host route

-manually configured static route to direct traffic to a specific destination device. The static router uses a destination IP and a /32 mask

-A host route allows for a more efficient process for packets that are directed to the router itself, rather than for packet forwarding.

Summary routes

A method where we create on summary route that represents multiple networks/subnets. Also called route aggregation or supernetting.

Advantages of summary routes

-saves memory

-saves bandwidth

-saves CPU cycles

-stability

What happens when a packet arrives at R1 with a destination interface

R1 decapsulates the packet and searches the routing tables for a matching destination network entry

Reasons a network may fail

- an interface can fail

- a service provider drops

-links can become oversaturated

-an administrator may enter a wrong configuration

Common troubleshooting commands

-ping

-traceroute

-show ip route

-show ip interface breif

-show cdp neighbors

Dynamic routing protocol components

-discovery of remote networks

-maintaining up to date routing

-choosing best path to destination networks

-ability to find new best path

Convergence time

the time it takes routers to share information, calculate best paths, and update routing tables

a network is not completely operable until it has converged

Convergence properties

the speed of propagation of routing information and the calculation of optimal paths.

Modern protocols

EIGRP and OSPF

Static routing advantages

-easy to implement in a small network

-very secure

-no routing algorithm or update required

Dynamic routing protocol usages

-best for large networks

-help network admin manage work.

Dynamic routing protocol advantages

Suitable in all topologies where multiple users are required

Independent of network size

Adapts topology to reroute traffic

IGP

Interior gateway protocols

-used for routing within autonomous systems

-RIP, EIGRP, OSPF, IS-IS

EGP

Exterior Gateway Protocols

-used for routing between autonomous systems

-official routing used by the internet

Distance vector protocols

RIP, EIGRP:

Use routers as sign posts along the path to the final destination

-not aware of network topology

-send updates even if nothing has changed

Link state protocol

having a complete map of the network topology. The sign posts along the way from source destination re not necessary because all routers are using an identical map of the network, using link state information for best path.

Link state protocol examples

OSPF, IS-IS

OSPF is popular in standards based routing where IS-IS is popular in provider networks

Classful routing

Do not send subnet mask information in their routing updates

RIP and IGRP are classful

cannot provide variable length subnet masks

Classless routing

include subnet mask information in the routing updates:

-RIPv2, EIGRP, OSPF, IS_IS

-Support VLSM

What is a metric

A measurable value that is assigned by the routing protocol to different routes based on the usefullness of that route, used to determine cost

Enable RIPv2

router rip

version 2

Route entries contain what information

route source

destination network

ongoing interface

[120/21]

Administrative distance and the metric

Route time stamp

time since route was updated

R 172.16.4.0 [120/2] via IP 00:00:12, G10/0/10

route source

destination network

administrative distance

metric

next hop

route timestamp

outgoing interface

Longest match

The best match is the route in the routing table with the longest matching number of far left matching bits with the destination IPv4 address

Hello Packets

In OSPF the first packet sent to identify neighbors, discover and elect default router and backup default router

LSA packet

Contain state and cost of each directly connected link. Routers flood their LSAs to adjacent neighbors

SPF tree

a topology made from received LSAs, eventually will hold all information on the topology of a network. from this tree the best paths are inserted to a routing table

How default router will be elcted

the router with the highest priority and router ID

Synchronizing OSPF database

DBD: Database datagram

LSAck: Ack of getting data

LSAck: Acking the Ack

Assigning a network an area

area 0

Passive interfaces

The passive interface router configuration mode command is used to prevent transmission of routing messages through the router interface but still allow that network to be advertised to other routers

Default interface bandwidth

1.54Mb/s