7. Managing A Cisco Internetwork Flashcards
In a router or switch, what is the bootstrap?
The bootstrap is stored in the microcode of the ROM, it boots up the device and then loads IOS
In a router or switch, what is the POST?
The Power On Self Test (POST) is stored in the microcode of the ROM, it checks the basic functionality of the device and determines which interfaces are present
In a router or switch, what is the ROM monitor?
This is stored in the microcode of the ROM, it is used for manufacturing, testing and troubleshooting
The ROMmon will run a mini-IOS if the IOS fails to load
In a router or switch what is the mini-IOS?
Mini-IOS (also called RXBOOT or boot loader) is a smaller version of IOS that can be used to bring up an interface and load IOS into flash memory.
The mini-IOS can also perform a few other maintenance operations
In a router or switch, what is stored in the RAM?
- Packet buffers
- ARP cache
- Routing tables
- Software and data structures that allow the device to function
- running-config
- IOS (in some devices)
In a router or switch, what is stored in the ROM hold?
- Bootstrap
- POST
- ROM monitor
- mini-IOS
ROM cannot be reprogrammed and is fixed at the manufacturing stage
In a router or switch, what is stored in the flash?
Why is this important?
- Cisco IOS
Flash is EEPROM (electrically erasable programmable read only memory)
- is not erased when the device is reloaded or powered off
- can be reprogrammed, but not a fast process
- used to store data that does not change in normal use (ie IOS)
In a router or switch, what is stored in the NVRAM?
- configuration register
- startup-config
Non Volatile RAM:
- can be written into easily
- is not erased when the device is reloaded or powered off
- is expensive, so a device will have a limited amount
In a router or switch, what is the configuration register?
The config register is used to define how the router will boot up
- default value is 0x2102
- this value tells the device to load the IOS from flash and startup-config from NVRAM
Study the router/switch boot sequence in detail
- The IOS device performs a POST (power on self test), this tests the hardware to verify that all components of the device are present and operational, it also takes stock of the different interfaces on the device. It is stored in and runs from ROM (read only memory)
- The boot strap in ROM locates and loads the Cisco IOS software by executing programs responsible for finding where each IOS program is located. By default the IOS software is loaded from flash memory in all Cisco devices.
- The IOS software looks for a valid configuration file stored in NVRAM. This file is called start-up-config and will be present only if an administrator has copied the running-config file into NVRAM previously.
- If a startup-config file is found (in NVRAM), the device will copy it into RAM and name it running-config. The device will use this file to run and should now be operational.
- If a startup-config file is not found in NVRAM, the device will broadcast out any interface that detects a carrier detect (CD) for a TFTP host looking for a configuration.
- When the TFTP search fails (which is typical), the device will start the setup mode configuration process.
- At this point the device must be configured manually from the console.
What command is used to verify the current configuration in DRAM?
router#show running-config
router#sh run
What command is used to verify the stored configuration in NVRAM?
router#show start-config
router#sh start
What command is used to copy the current configuration into NVRAM?
router#copy running-config
router#copy sh run
Or
router#write
router#wr
What command is used to copy the current configuration to a TFTP server?
router#copy running-config tftp
router#copy run tftp
What command is used to restore a configuration from a TFTP server?
router#copy tftp running-config
router#copy tftp run
What command is used to erase a stored configuration in NVRAM?
router#erase startup-config
Note that no abbreviations are valid for this operation
What prerequisite information do you need to configure DHCP?
- Network and mask for each LAN. All addresses in a subnet will be leased to host by default.
- Reserved/Excluded Addresses These can be for printers, servers, routers, etc, these addresses will not be handed out to hosts. It is common practice to reserve the first address of each subnet for the router.
- Default router address
- DNS server address(es)
What are the steps needed to configure DHCP?
- Exclude the addresses you want to reserve
- Create a pool for each LAN using a unique name
- Choose the network ID and subnet mask for the DHCP pool that the server will use to provide addresses to host.
- Add to the address used for the default gateway of the subnet
- Provide the DNS server address(es)
- If you don’t want to use the default lease time of 24 hours set a new lease time in days, hours and minutes
What are the IOS commands needed to configure DHCP?
Using 129.168.10.0/24 as our LAN
sw(config)#ip dhcp excluded-address 192.168.10.1 192.168.10.10
sw(config)#ip dhcp pool Sales
sw(dhcp-config)#network 192.168.10.0 255.255.255.0
sw(dhcp-config)#default-router 192.168.10.1
sw(dhcp-config)#dns-server 4.4.4.4
Optional
sw(dhcp-config)#lease 3 12 27
sw(dhcp-config)#option 66 ascii tftp.domain.com
Option 66 is used to send a TFTP server address to the DHCP clients, it issued for VoIP, auto installs and needs to be FQDN (full qualified domain name)
How can a DHCP server serve multiple networks?
A DHCP server can maintain numerous pools, each pool is configured for a different LAN
If a client is outside the broadcast domain of the DHCP server, its default router can be configured to point to the DHCP server with the command
router(config)#int fa0/0
router(config-if)#ip helper-address a.b.c.d
What IOS commands can be used to verify DHCP?
show ip dhcp
binding
- list information about each IP address currently leased to a client
pool poolname
- list the configured range of IP addresses
- list statistics for the currently leased addresses
- display the high watermark for leases
server statistics
- list DHCP server statistics (there’s a lot)
conflict
- display ip address conflicts??
When trying to telnet into a device you receive the error
Password required, but none set
How can you resolve this error?
VTY ports are configured as login by default, meaning that you have to either
- set the VTY password or
- use the no login command
What commands set a password for telnet access?
sw(config)#line vty 0 15
sw(config-line)#password passwd
sw(config-line)#login
What command shows active telnet connections to remote devices?
sw#show sessions
What command shows active console and VTY ports in use?
sw#show users
What command(s) close(s) a remote telnet session?
sw#exit
sw#disconnect X
How do you resolve a host name into an IP address?
- Use/build a DNS server
- Build a host table on each router
rt(config)#ip host hostname a.b.c.d
rt(config)#ip host hostname2 e.f.g.h
What command displays the host table?
rt#show hosts
If perm is displayed in Flags, this means the entry was manually configured
If temp is displayed, this means the entry was resolved by DNS
What command is used to remove a host name from the hosts table?
rt(config)#no ip host hostname
What commands would you use to set up use of a DNS server?
sw(config)#ip domain-lookup
sw(config)#ip name-server a.b.c.d
sw(config)#ip domain-name lab.com
What command is used to debug device operation?
sw#debug all
This will severely impact device performance
sw#debug option
This will only show debug output for the selected option, ie arp, cdp, ip icmp, etc
What commands can be used to deactivate debug output?
sw#no debug option
sw#no debug all
sw#undebug all
sw#un all
What command can be used to check device utilisation?
sw#show processes
sw#show processes cpu
What keyboard controls can be used to switch between telnet sessions?
Ctrl + Shift + 6 then X
What command is used to configure basic syslog with debugging level as default
rt(config)#logging a.b.c.d
What are the levels of logging in syslog?
rt(config)#logging trap X
0 Emergencies - System is unstable
1 Alerts - Immediate action needed
2 Critical - Critical conditions
3 Errors - Error conditions
4 Warnings - Warning conditions
5 Notifications - Normal but significant
6 Informational - Informational messages
7 Debugging - Debugging messages
What commands are used to configure NTP (network time protocol)?
rt(config)#service timestamps log datetime msec
rt(config)#ntp server a.b.c.d version 4
What are CDP and LLDP?
What are they useful for?
Cisco Discovery Protocol is proprietary layer 2 protocol used to advertise device information to connected peers, this is useful for documentation and troubleshooting
Link Layer Discover Protocol is an open layer 2 neighbour protocol for advertising device information to directly connected peers/neighbours
What information is provided by
sw#show cdp neighbors
- device ID
- local interface
- hold time
- capability
- platform
- port ID (remote interface)
