Vol 1 Part 5: Operating Cisco Routers Flashcards
What are the three different types of common networks?
Ethernet LAN, Ethernet WAN, Serial WAN
What are SOHO routers able to do all at one time?
Route, Switch, VPN, and serve as a WAP
True or False: Routers share many of the same CLI features as switches (ie user and enable mode, conf t, shutdown and no shutdown, line colse 0, interface FE0/1 etc.)
TRUE
Unlike a VLAN interface on a switch, IP addresses are configured how?
IP addresses are configured on physical interfaces on the router
What command is used to show the interfaces on a router?
- show ip interface brief (shows the layer 1 and layer 2 status in addition to interfaces)
- show interfaces
- show run (much less efficient)
What does the line status and protocol status refer to when looking at router interface status codes?
line status- the layer 1 status
protocol status- the layer 2 status.
Explain the 4 types of line/protocol statuses
Admin down, down- shutdown command
down, down- no shutdown, but there is an issue with there is a problem at the physical layer
up, down- data link layer problems ie. one router is using PPP and the other HDLC
up, up- FMC
Most Cisco router interfaces default to a shutdown state. How would you enable it?
By using the no shutdown command
What must you do before a router can rout packets in and out of the interface?
Configure an IP address and subnet mask on the interface
What are the two types of encapsulation and what are the differences in each?
Point to Point Protocol (PPP) and High-Level Data Link Layer Protocol (HDLC)
PPP is dynamic, synchronous and asynchronous, authenticated, byte oriented, point to point, and vendor neutral.
HDLC is static, synchronous, not authenticated, bit oriented point to point or multipoint, and Cisco proprietary.
What is the router auxiliary port used for on a router?
It connects to an analog modem for remote dial-in CLI access. Line Aux 0 will reach the auxiliary port, much like line con 0 accesses the CLI.
What is an Small Form factor Pluggable (SFP) and why is it important?
The SFP refers to the pluggable network interface module on the router. It is the slot where the user can link the router to the switch. If you do not know the SFP, then you won’t know what kind of cabling to use or what your speed is on that port.
How does a host device determine if a packet it is preparing to send out resides in its own subnet?
By looking at the destination IP and comparing it to the host’s IP and subnet mask.
What does a host device do if the packet it is preparing to send resides outside of its subnet?
The packet is sent to the default gateway
When the router is determining where to route a packet based on the destination IP, what two things must it do?
- Check the routing table for a valid matching route
2. Identify the outgoing interface and possibly, the next hop router
What steps does a router take when sending a packet?
- Check the FCS for errors
- de-encapsulate the packet from inside the data-link frame
- Check routing table for a valid match
- Encapsulate the packet into a data-link frame appropriate for the outgoing interface
- transmit the frame out the outgoing interface
What command is used to configure a static route?
ip route (global command)
Cisco routers automatically add their own routes connected directly to them assuming that?
The interface is up/up and the interface has an IP address assigned through the ip address interface subcommand
What is the term used to refer to a connected route within the same interface, what is the CIDR, and why do we use them?
Host route. /32 CIDR. Helps routers more efficiently forward packets to itself.
How do you know if a route within a routers ARP table has been statically assigned?
The letter “S” is used as a route code
When is a static route considered a network route?
When the destination listed in the ip route command defines a subnet or entire class network. Conversely, it is considered a host route when it matches a single ip.
Why don’t static default routes consume bandwidth?
They only route to one destination for all packets.
What command can you use to find the best route between routers?
show ip route address
What route has the lowest administrative distance?
Connected
What command reaches the auxiliary port on the router for configuration?
Line aux 0
What do routers use for each VLAN being trunked from the switch?
sub interfaces
What would the command look like to configure a sub interface on a gigabit ethernet interface on a router for VLAN 10?
Interface g0/0.10
What are the two ways to configure a sub interface on a router?
- Directly on the physical interface (interface g0/0.10)
2. encapsulation dot1q vlan-id native
On a layer 3 switch, which command is used in global config mode in order to change the switch forwarding ASIC settings to make space for IPv4 routes?
Sdm prefer lanbase-routing
On a layer 3 switch, what are the commands you must use after you set the switch to lanbase routing?
- reload
- ip routing
-
configure SVIs as needed ie.
interface VLAN 58
ip address 58.0.0.1 255.255.255.0
no shut
If a show ip route does not work, what are the two ways we can check to see if the configuration is correct?
- ensure the “sdm prefer” command was utilized
2. ensure “ip routing” is configured
When only a single network needs to connect an interface to a router, what port can we use?
A routed port
How do you configure a routed port on a switch?
By using the “no switchport” command
What are the steps you must take to confirm that a routed port has properly been configred?
- show interfaces
- show interfaces status (look for routed instead of access or the trunked VLAN)
- show ip route (look for the port as the outgoing port to the router)
- show interfaces interface switchport (confirms the port is a routed port).
For layer 3 EtherChannels, what command is used to include the ports you are using to configure EtherChannel?
channel-group
Each physical port you use for layer 3 etherchannel configuration must have what command configured on it?
no switchport
The PortChannel interface needs what three things for layer 3 etherchannel?
- interface port-channel port number
- no switchport
- an ip address and subnet mask
What command would you use to verify the up/up status and the IP address with appropriate CIDR prefix when using layer 3 etherchannel?
show interfaces port-channel port number
What primary command enables layer 3 routing on a switch?
ip routing
If a host cannot ping a router outside of your subnet, what should you do first in order to begin troubleshooting?
ping the nearest router first (typically the default gateway)
A ping sends a request and gets a reply from whatever device is trying to be reached. How long does the ping take, how many pings occur, and why might the first ping fail?
- 2 seconds. 1 for the request, one for the reply.
- 5 echo requests total.
- ARP, as it takes longer to resolve than the ping is willing to wait. All subsequent echo requests should work.
When pinging a host device from a router, what interface will the router use?
The closest interface to the host
What is an extended ping?
a ping with no ip address following it
What command sends ICMP echo request to each router int he path from a source host?
traceroute
What does traceroute use in the layer 3 header?
The Time To Live field
