9 - Routers Flashcards
What are the different forwarding mechanisms on a router?
process switching
fast switching
cisco express forwarding
Describe process switching.
uses the routers cpu to determine the next hop and forwarding interface, typically on used for difficult packets that require encryption or nat, or destinations that have not been entered into the route cache
Describe fast switching.
does not use the routers cpu, handles significantly higher throughput than process switching
Describe CEF or cisco express forwarding?
Uses FIB or forwarding information table, the fib table contains all the ip prefixes and remains synced with the ip routing table
What command is used to determine the type of forwarding mechanism that is enabled on the interface?
sh ip interface fa0/0
What are some common features for cisco routers?
- modularity
- low port count
- most ports are typically routed ports
- aux port
- compact flash storage
What is an aui port?
15 pin port attachment unit interface
what are bri ports?
used to connect to an isdn line
What does nm stand for on a cisco router?
Network Module
What does wic stand for on a cisco router?
Wan Interface Card
How many interfaces of a router can be on a single subnet?
one
What is the meaning of interface status up and line protocol up?
both the interface and protocol are working as intended
What is the meaning of interface status up and line protocol down?
layer 2 problem exists
What is the meaning of interface status down and line protocol down?
layer 1 problem exists
What is the meaning of interface status administratively down and line protocol down?
the interface was configured with the shutdown command
What layer do encapsulation protocols operate?
data link layer
What are the two primary encapsulation methods in cisco serial interfaces?
HDLC or high level data link
PPP point to point protocol
What encapsulation method is default for all synchronous serial ports on cisco devices?
HDLC
Is cisco’s interpretation of hdlc proprietary?
yes, uses a proprietary field that indicates the payload protocol
What encapsulation method is used with multi vendor implementations?
PPP
What are the protocols used by PPP?
LCP link control protocol
NCP network control protocol
What does LCP do?
configures authentication, compression, and other options used by PPP
What does NCP do?
negotiates which lan protocols will be encapsulated
What are some examples of the authentication used in PPP?
Chap or challenge handshake authentication protocol
PAP or password authentication protocol
When does authentication take place in PPP?
After lcp and before ncp
What does DCE stand for?
data communications equipment
What does DTE stand for?
data terminating equipment
What side of the connection has to have the clocking applied to it?
DCE
What command is used to determine what side the clocking needs to be applied?
show controllers
what command is used to apply a clock rate for a serial connection?
clock rate
What does csu/dsu stand for?
channel service unit/data service unit
What is the meaning of interface status up and line protocol up (looped)?
a loop exists in the circuit
What is the meaning of interface status up and line protocol down (disabled)?
interface detected a high rate of errors
What are keepalives used for?
to determine whether a link is usable
When using PPP encapsulation, what needs to be configured differently between the two devices?
the hostname, because of the authentication using the hostname
What command can be used to troubleshoot PPP negotiation?
debug ppp negotiation
What is the local database called on a cisco router?
routing table
What are the four general types of routes in a routing table?
directly connected routes
static routes
dynamic routes
default routes
What is displayed in the routing table for directly connected routes?
the interface and not a next hop ip address along with the network prefix
Is the subnet mask displayed with the network prefix in the routing table?
yes unless its a classful network
What type of general routes contain and administrative distance?
statically
dynamic
What is another name for the default route?
gateway of last resort
What has to happen on the interface before it has a directly connected route in the routing table?
active state
What is used when you have multiple routes to a network?
the administrative distance
What are the four types of IPv6 static routes?
recursive
directly attached
fully specified
floating
What makes a floating ipv6 static route?
either a recursive, directly attached, or specified with a higher AD value
Is ipv6 enabled by default on a cisco router?
no
What is a dynamic route?
a path to a network that a router learns through routing updates from other routers
If there are two routes to the same network with the same routing protocol, ie same administrative distance, what is used to determine the best route?
the metric
rip metric is determined by hop count
eigrp metric is determined by bandwidth, delay, load, and reliability
ospf metric is determined uses cost
What is the AD for a directly connected route?
0
What is the AD for a static route?
1
What is the AD for an EIGRP route?
90
What is the AD for an OSPF route?
110
What is the AD for a RIP route?
120
What is the AD for an unknown or unreliable route?
255
What is a default route used for?
send packets that are destined for a location that is not listed elsewhere in the routing table
What is a goal of default routes?
keep the routing table small
What is a downside to using an interface for as a destination in the default route?
ARP requests are created for each destination address it sends through the default route which can cause high processor utilization and a large arp cache
How do you create the gateway of last resort on a router that has ip routing disabled?
ip default-gateway
Where is the gateway of last resort typically listed in the routing table?
before the first route
