CCNP Troubleshooting Flashcards
Command: Display routing protocols status.
show ip protocols
Command debug | EIGRP: displays all EIGRP messages that are sent and received on a router
debug eigrp packets
Common reasons that the EIGRP adjacency fails follow:
- AS mismatch
- K value mismatch
- Misconfigured network command
- Passive interface
- Authentication misconfiguration
- Security filtering
- Unidirectional link
- Misconfigured subnet mask
Command | EIGRP: Display interfaces that are running EIGRP
show ip eigrp interfaces
Which command is used to verify the TCP connection for a BGP session?
show tcp brief | include 179
You can use several methods at the same time. For the inbound updates, the order in which the methods are applied follows:
- Route-map
- Filter-list
- Prefix-list/distribute-list
For the outbound updates the order follows:
- Prefix-list/distribute-list
- Filter-list
- Route-map
Command: Display the BGP table. Add the summary keyword to display the status.
show ip bgp [summary]
Command: Display the received routes by the BGP peer.
show ip bgp neighbors ip-address routes
Command: Display the advertised routes by the BGP peer.
show ip bgp neighbors ip-address advertised-routes
Command: Display information about the processing of BGP updates or display BGP events.
debug ip bgp {updates | events}
There are several possible reasons for an erroneous clock on network devices:
- Access control lists do not permit UDP port 123 packets.
- An NTP authentication mismatch exists.
- Time zone and summer time misconfigurations are on the router.
- The time server is not accessible.
- The NTP server is misconfigured.
- The NTP server lost sync.
- High CPU utilization is present.
- A high offset is between the server and the client.
- The stratum is too high.
NTP protocol and port number
NTP uses UDP port 123.
NTP authentication method
MD5
Command: Display the NTP status.
show ntp status
Display the NTP associations
show ntp associations
Display the NTP events that occur.
debug ntp events
The server that is used to synchronize the clock is indicated with the ______ at the beginning of the line
asterisk (in the “show ntp association” output)
For the inbound updates the order follows:
- Route-map
- Filter-list
- Prefix-list/distribute-list
Command: Check if routing is enabled on the multilayer switch
show running-config | include ip routing
Command: To add the DNS server IP address to the DHCP configuration
dns-server 209.165.201.209
Command: DNS manual configuration in DNS client
ip name-server 209.165.201.209
Command: renovar dhcp
renew dhcp ethernet 0/0
Command: reload in certain time
reload in 15
Command: calcel programed device reload
reload cancel
DNS port
53 udp/tcp
FTP ports
20-21 tcp
Telnet port
23 tcp
SMTP port
25 tcp/udp
DHCP port
67-68 udp
TFTP port
69 udp
SNMP port
161-162 udp
Microsoft SQL ports
1433-1434
Command: replace the running configuration with the startup configuration, which will override, append, or delete configuration elements that are different.
configure replace startup-config
Command: The startup-configuration commands are added to the running configuration. However, commands that already exist in the running configuration but that are not in the startup configuration are not removed.
copy startup-config running-config
displays a summary of information about EIGRP address families
show eigrp plugins
EIGRP | reveals information for all address families that are configured.
show ip eigrp protocols
EIGRP | displays a list of network prefixes and the related information.
show eigrp address-family {ipv4 | ipv6} [autonomous-system-number] [multicast] accounting
EIGRP | displays an interface-specific configuration.
show eigrp address-family {ipv4 | ipv6} interfaces detail [interface-type interface-number]
EIGRP | displays information about all summary routes.
show eigrp address-family {ipv4 | ipv6} topology route-type summary
EIGRP | displays information on passive interfaces and a list of network prefixes.
show ip protocols and show running-config | section router eigrp
EIGRP | displays all packets except hellos.
debug eigrp packet terse
EIGRP | displays information about the stub status of the peer routers.
debug eigrp packet stub
EIGRP | The remote router advertises only its connected routes.
eigrp stub connected
EIGRP | The remote router advertises only its static routes.
eigrp stub static
EIGRP | The remote router advertises only other protocols and AS routes.
eigrp stub redistribute
EIGRP | The remote router advertises only summary routes.
eigrp stub summary
EIGRP | The remote router does not advertise routes.
eigrp stub receive-only
EIGRP | display the stub status of neighbors and which routes are advertised.
show ip eigrp neighbors detail
debug | to display all EIGRP packets except hellos.
debug eigrp packet terse
debug eigrp | display information about the stub status of the peer routers.
debug eigrp packet stub
check whether routing is enabled on the device using:
show ip route—no output means routing is not enabled.
show running-config—the lack of the “no ip routing” statement; cef statements: “ip cef” or “ipv6 cef” mean IP routing is enabled.
There are three ways to configure default route information on Layer 2 and multilayer devices:
- Switch# ip route 0.0.0.0 0.0.0.0 {ip-address | interface-type interface-number [ip-address]}
Use this command when routing is enabled on the device.
- Switch# ip default-network network-number
Use this legacy command when routing is enabled on the device.
- Switch# ip default-gateway network-number
Use this command on pure Layer 2 devices.
The recipe to application optimization is a four-step cycle
Step 1. Baseline application traffic.
Step 2. Optimize the network.
Step 3. Measure, adjust, and verify.
Step 4. Deploy new applications.
Netflow | The seven fields that need to match for packets to be considered part of the same flow are as follows:
- Source IP Address
- Destination IP Address
- Source Port (protocol dependent)
- Destination Port (protocol dependent)
- Protocol (Layer 3 or 4)
- Type of Service (ToS) Value (differentiated services code point [DSCP])
- Input Interface
To implement IP SLA network performance measurement, you need to perform the following tasks:
- Enable the IP SLA responder, if required.
- Configure the required IP SLA operation type.
- Configure any options available for the specified operation type.
- Configure threshold conditions, if required.
- Schedule the operation to run, and then let the operation run for a period of time to gather statistics.
- Display and interpret the results of the operation using the Cisco IOS CLI or an NMS, with SNMP.
For Cisco AutoQoS to work certain requirements must be met, as follows:
- CEF must be enable on the interface.
- The interface (or subinterface) must have an IP address configured.
- For serial interfaces (or subinterfaces) configure the appropriate bandwidth.
- On point-to-point serial interfaces, both sides must be configured AutoQoS.
Troubleshooting performance problems is a three-step process:
Step 1. Assessing whether the problem is technical in nature
Step 2. Isolating the performance problem to a device, link, or component
Step 3. Diagnosing and resolving the performance degradation at the component level
The following events cause spikes in the CPU utilization:
- Processor-intensive Cisco IOS commands
- Routing protocol update processing
- SNMP polling
Some common interface and wiring problems are as follows:
- No cable connected
- Wrong port
- Device has no power
- Wrong cable type
- Bad cable
- Loose connections
- Patch panels
- Faulty media converters
- Bad or wrong GBIC
Common symptoms of a router CPU that is too busy is that the router fails to respond to certain service requests. In those situations, the router might exhibit the following behaviors:
- Slow response to Telnet requests or to the commands issued in active Telnet sessions
- Slow response to commands issued on the console
- High latency on ping responses or too many ping timeouts
- Failure to send routing protocol packets to other routers
When troubleshooting CEF, you always want to check and verify the following:
- Is CEF enabled globally and per interface?
- Is there a FIB entry for a given network destination?
- Is there a next hop associated with this entry?
- Is there an adjacency entry for this next hop?
Symptoms of memory-allocation failures include the following:
- Messages such as %SYS–2–MALLOCFAIL: Memory allocation of 1028 bytes failed from 0x6015EC84, Pool Processor, alignment 0 display in the router logs.
- Not getting any output from show commands.
- Receiving Low on memory messages.
- Receiving the message Unable to create EXEC – no memory or too many processes on the console.
Some of the main reasons for memory problems are as follows:
- Memory size does not support the Cisco IOS Software image
- Memory-leak bug
- Security-related problems
- Memory-allocation failure at process = interrupt level error message
- Buffer-leak bug
