table.
Content 3.3
Troubleshooting Routing Protocols 3.3.1 Routing
protocol troubleshooting process All routing protocol
troubleshooting should begin with a logical sequence, or
process flow. This process flow is not a rigid outline for
troubleshooting an internetwork. However, it is a foundation
from which a network administrator can build a problem-solving
process to suit a particular environment. - When
analyzing a network failure, make a clear problem statement.
- Gather the facts needed to help isolate possible
causes.
- Consider possible problems based on the
facts that have been gathered.
- Create an action plan
based on the remaining potential problems.
- Implement
the action plan, performing each step carefully while testing
to see whether the symptom disappears.
- Analyze the
results to determine whether the problem has been resolved. If
it has, then the process is complete.
- If the problem
has not been resolved, create an action plan based on the next
most likely problem in the list. Return to Step 4, change one
variable at a time, and repeat the process until the problem is
solved.
- Once the actual cause of the problem is
identified, try to solve it.
Cisco routers provide
numerous integrated commands to assist in monitoring and
troubleshooting an internetwork: - show commands
help monitor installation behavior and normal network behavior,
as well as isolate problem areas
- debug
commands assist in the isolation of protocol and configuration
problems
- TCP/IP network tools such as ping,
traceroute, and telnet
Cisco IOS show
commands are among the most important tools for understanding
the status of a router, detecting neighboring routers,
monitoring the network in general, and isolating problems in
the network. EXEC debug commands can provide a wealth of
information about interface traffic, internal error messages,
protocol-specific diagnostic packets, and other useful
troubleshooting data. Use debug commands to isolate
problems, not to monitor normal network operation. Only use
debug commands to look for specific types of traffic or
problems. Before using the debug command, narrow the
problems to a likely subset of causes. Use the show
debugging command to view which debugging features are
enabled. Web Links Troubleshooting EIGRP
http://www.cisco.com/en/US/tech/ tk826/tk365/technologies_
tech_ note09186a0080094613.shtml
Content
3.3 Troubleshooting Routing
Protocols 3.3.2 Troubleshooting RIP
configuration The most common problem found in Routing
Information Protocol (RIP) that prevents RIP routes from being
advertised is the variable-length subnet mask (VLSM). This is
because RIP Version 1 does not support VLSM. If the RIP routes
are not being advertised, check the following: - Layer 1
or Layer 2 connectivity issues exist.
- VLSM subnetting
is configured. VLSM subnetting cannot be used with RIP
v1.
- Mismatched RIP v1 and RIP v2 routing
configurations exist.
- Network statements are missing
or incorrectly assigned.
- The outgoing interface is
down.
- The advertised network interface is down.
The show ip protocols command provides information
about the parameters and current state of the active routing
protocol process. RIP sends updates to the interfaces in the
specified networks. If interface FastEthernet 0/1 was
configured but the network was not added to RIP routing, no
updates would be sent out or received from the interface. Use
the debug ip rip EXEC command to display information on
RIP routing transactions. The no debug ip rip, no
debug all, or undebug all commands will turn off all
debugging. Figure shows that the router being debugged has
received an update from another router at source address
192.168.3.1. That router sent information about two
destinations in the routing table update. The router being
debugged also sent updates. Both routers broadcasted address
255.255.255.255 as the destination. The number in parentheses
is the source address encapsulated into the IP header. An entry
most likely caused by a malformed packet from the transmitter
is shown in the following output: RIP: bad version 128 from
160.89.80.43 Web Links Missing RIP Routes? Popular
Troubleshooting Techniques http://www.cisco.com/en/US/about/
ac123/ac114/ac173/ac169/about_
cisco_packet_enterprise_solution
09186a00800a3453.html
Content 3.3 Troubleshooting
Routing Protocols 3.3.3 Troubleshooting IGRP
configuration Interior Gateway Routing Protocol (IGRP) is
an advanced distance vector routing protocol developed by Cisco
in the middle 1980s. IGRP has several features that
differentiate it from other distance vector routing protocols
such as RIP. Use the router igrp autonomous-system
command to enable the IGRP routing process:
R1(config)#router igrp 100 Use the router configuration
network network-number command to enable
interfaces to participate in the IGRP update process:
R1(config-router)#network 172.30.0.0
R1(config-router)#network 192.168.3.0 Verify IGRP
configuration with the show running-configuration and
show ip protocols commands: R1#show ip protocols
Verify IGRP operation with the show ip route command:
R1#show ip route If IGRP does not appear to be working
correctly, check the following: - Layer 1 or Layer 2
connectivity issues exist.
- Autonomous system numbers
on IGRP routers are mismatched.
- Network statements
are missing or incorrectly assigned.
- The outgoing
interface is down.
- The advertised network interface
is down.
To view IGRP debugging information, use the
following commands: - debug ip igrp transactions
[host ip address] to view IGRP transaction
information
- debug ip igrp events [host ip
address] to view routing update information
To
turn off debugging, use the no debug ip igrp command. If
a network becomes inaccessible, routers running IGRP send
triggered updates to neighbors to inform them. A neighbor
router will then respond with poison reverse updates and keep
the suspect network in a holddown state for 280 seconds. Web
Links IGRP http://www.cisco.com/en/US/tech/
tk365/tk352/technologies_tech_note
09186a0080093f0b.shtml
Content 3.3 Troubleshooting
Routing Protocols 3.3.4 Troubleshooting EIGRP
configuration Normal EIGRP operation is stable, efficient
in bandwidth utilization, and relatively simple to monitor and
troubleshoot. Use the router eigrp autonomous-system
command to enable the EIGRP routing process:
R1(config)#router eigrp 100 To exchange routing updates,
each router in the EIGRP network must be configured with the
same autonomous system number. Use the router configuration
network network-number command to enable
interfaces to participate in the EIGRP update process:
R1(config-router)#network 172.30.0.0
R1(config-router)#network 192.168.3.0 Verify EIGRP
configuration with the show running-configuration and
show ip protocols commands: R1#show ip protocols