Tài liệu học CCNA kỳ 2 mod9 routertroubleshooting

Module 9 – Basic Router Troubleshooting Overview Students completing this module should be able to: routes installed on the router data through the network source and destination station

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Module 9 – Basic Router

Troubleshooting

Overview

Students completing this module should be able to:

routes installed on the router

data through the network

source and destination stations

problems

routing issues

networks

is attached

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NIIT-ICT Hanoi info@niithanoi.vn 3

9.1 Examining the Routing Table

We have covered these and others in more depth in previous

modules and the presentation on the Structure and Lookup

Process of the Routing Table.

• 9.1.1 The show ip route Command

• 9.1.2 Determining the gateway of last resort

• 9.1.3 Determining route source and destination

• 9.1.4 Determining L2 and L3 addresses

• 9.1.5 Determining the route administrative distance

• 9.1.6 Determining the route metric

• 9.1.7 Determining the route next hop

• 9.1.8 Determining the last routing update

• 9.1.9 Observing multiple paths to destination

Static Routing

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Dynamic Routing

Default Routes

• There a couple of items of misinformation in this section

that we need to address.

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Default Routes – ip default-network command

The ip default-network command:

route 0.0.0.0 0.0.0.0)

specific route to that network or a 0.0.0.0/0 default route!

Default Routes - RIP

With RIP:

• Use 0.0.0.0/0 static route

• Use default-information originate (IOS 12.0 and later)

ip route 0.0.0.0 0.0.0.0 s0 router rip

network 172.16.0.0 network 192.168.17.0 default-information originate

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Determining route source and destination

Path Switching

functions:

packet

• Note: Data link addresses have been abbreviated.

Path Switching and Packet Forwarding

RTA RTB RTC 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24

e0 s0 s0 s1 s0 e0 1 1 2 1 2 1

Data link destination address Data link source address Other data link fields IP Destination Address IP Source Address Other IP fields and data

Data Link Frame = Data Link Header + IP Packet

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From Host X to Router RTA

Ethernet) with RTA’s Ethernet 0 interface’s MAC address as the data link

destination address

How does Host X know or get RTA’s Ethernet address?

operation and compares it to its own ip address and subnet mask

packet in its ARP cache – sending out an ARP request if it is not there

gateway in its ARP cache – sending out an ARP request if it is not there

The Process and the Protocol”

192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

e0 00-10

e0 0C-22 e0

0B-31 e1

Y

00-10 0A-10 192.168.4.10 192.168.1.10

RTA to RTB

1 RTA looks up the IP destination address in its routing table

e1

next-hop-ip address with a destination MAC address

2 RTA looks up the next-hop-ip address of 192.168.2.2 in its ARP cache

request out e1 RTB would send back an ARP reply, so RTA can update its

ARP cache with an entry for 192.168.2.2

192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24

e0 00-10

e0 0C-22 e0

0B-31 e1

00-20

s0 s0

0B-31 00-20 192.168.4.10 192.168.1.10

1

2

3

RTA Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 0 Dir.Conn e0 192.168.2.0/24 0 Dir.Conn e1 192.168.3.0/24 1 192.168.2.2 e1 192.168.4.0/24 2 192.168.2.2 e1

RTA ARP Cache

IP Address MAC Address

192.168.2.2 0B-31

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RTA to RTB (continued)

3 Data link destination address and frame encapsulation

RTA uses the MAC address for the destination MAC address in the

re-encapsulated Ethernet frame

The frame is now forwarded out Ethernet 1 (as specified in RTA’s routing table

used for the data link address and exit interface, to forward the packet in a new

data link frame

192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

e0 00-10

e0 0C-22 e0

0B-31 e1

Y

0B-31 00-20 192.168.4.10 192.168.1.10

1

2

3

RTA Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 0 Dir.Conn e0 192.168.2.0/24 0 Dir.Conn e1 192.168.3.0/24 1 192.168.2.2 e1 192.168.4.0/24 2 192.168.2.2 e1

RTA ARP Cache

192.168.2.2 0B-31

192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24

e0 00-10

e0 0C-22 e0

0B-31 e1

00-20

s0 s0

1

RTB to RTC

1 RTB looks up the IP destination address in its routing table

s0 (serial 0)

resolve the next-hop-ip address with a destination MAC address

RTB Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 1 192.168.2.1 e0 192.168.2.0/24 0 Dir.Conn e0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 1 192.168.3.2 s0

2

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192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

e0 00-10

e0 0C-22 e0

0B-31 e1

Y

1

RTB to RTC

2 Data link destination address and frame encapsulation.

Table process does not even look at the next-hop IP address.

out.

using the proper serial encapsulation (HDLC, PPP, etc.).

one other end of the pipe and the frame is now forwarded out serial 0.

RTB Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 1 192.168.2.1 e0 192.168.2.0/24 0 Dir.Conn e0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 1 192.168.3.2 s0

2

192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24

e0 00-10

e0 0C-22 e0

0B-31 e1

00-20

s0 s0

0B-20 0C-22 192.168.4.10 192.168.1.10

RTC to Host Y

1 RTC looks up the IP destination address in its routing table

interfaces and it can sent the packet directly to the destination and not another

router

resolve the destination ip address with a destination MAC address

2 RTC looks up the destination ip address of 192.168.4.10 in its ARP cache

request out e0 Host Y would send back an ARP reply, so RTC can update its

ARP cache with an entry for 192.168.4.10

RTC ARP Cache

192.168.4.10 0B-20

RTC Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 2 192.168.3.1 s0 192.168.2.0/24 1 192.168.3.1 s0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 0 Dir.Conn e0

1 3

2

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192.168.1.10/24

0A-10

192.168.4.10/24 0B-20

e0 00-10

e0 0C-22 e0

0B-31 e1

Y

0B-20 0C-22 192.168.4.10 192.168.1.10

RTC to Host Y (continued)

3 Data link destination address and frame encapsulation

RTC uses the MAC address for the destination MAC address in the

re-encapsulated Ethernet frame

The frame is now forwarded out Ethernet 0 (as specified in RTA’s routing table

RTC ARP Cache

192.168.4.10 0B-20

RTC Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 2 192.168.3.1 s0 192.168.2.0/24 1 192.168.3.1 s0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 0 Dir.Conn e0

1 3

2

Determining the route administrative distance

particular destination ”

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Routing Metrics - Corrections

• MTU is not and has never been used as a routing metric

with RIP, IGRP, EIGRP, OSPF, IS-IS, or BGP.

Observing multiple paths to destination

destination network, four by default.

Distance Vector Routing Protocols, Part 1 of 2: Distance Vector

Routing and RIP)

routes, as you cannot compare RIP metrics with IGRP metrics.

another, static routes over dynamic, IGRP over RIP, etc.

curriculum.

IGRP and EIGRP?

ote09186a008009437d.shtml

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Network Testing

Network Testing and Troubleshooting

– Lab

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Different Models

Testing using the OSI Model

Layer 1 errors can include:

crossover cables, and straight-through cables correctly)

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• Routing protocol not enabled

• Wrong routing protocol enabled

• Incorrect IP addresses

• Incorrect subnet masks

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Various commands

• These commands show various levels of connectivity or

lack of connectivity:

– Traceroute

– Telnet

– Show interfaces

– Show cdp neighbors

– Show ip protocols

– Debug

– Show running-config

• What do these commands tell you?

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