final review Flashcards
PVST hello timer?
2 seconds
LLDP hold timer?
LLDP hello timer?
hold - 120 secs (x4)
hello - 30 secs
Root bridge’s interfaces have what cost?
0
PVST takes 50 seconds by default, because of what 3 other timers?
15s - learning state timer
15s - delay timer
20s - max age timer
how is EIGRP metric calculated?
lowest segment bandwidth
sum of segment delays
EIGRP routing table contains only what?
successors
what is a successor?
best path to destination network.
what is a feasible successor?
best loop-free backup route with lower AD than successor’s advertised distance
what is a feasible distance?
the best metric along a path (advertised + next hop)
what is an advertised distance?
the metric advertised by the next hop router
how is OSPF metric calculated?
Cost/metric = Reference Bandwidth of 100 Mbps divided by interface bandwidth.
(For example, in the case of 10 Mbps Ethernet , OSPF Metric Cost value is 100 Mbps / 10 Mbps = 10)
What is the default CDP hold/announcements timer?
hold - 180 secs (x3)
announcement - 60 sec
What kind of errors will you see in Duplex Mismatch?
- The half-duplex side of the link will experience increased collision rates
- The full-duplex side of the link will have a large number of CRC errors.
What can cause down/down?
bad cable/connector, speed mismatch
What is the difference between an OSPF ABR and ASBR?
ABR - Area Border Router, lets OSPF router know the edges of an OSPF area.
ASBR - Autonomous System Border Router, lets devices know end of AS and where default gateway is located.
what is the only dhcp command that doesn’t need ‘ip’ at the start?
(dhcp-config)#domain-name example.com
Which OSPF network types have a default hello/dead timer of 10/40 seconds?
- broadcast
- point-to-point
Which OSPF network types have a default hello/dead timer of 30/120 seconds?
-non-broadcast
What OSPF network type is enabled by default for FDDI and Ethernet interfaces?
broadcast
What OSPF network type is enabled by default for HDLC and PPP serial interface?
point-to-point
What OSPF network type is enabled by default for X.25 and frame relay interface?
non-broadcast
Router stuck in exstart/exchange
MTU mismatch/duplicate IDs
router stuck in loading
corrupted LSR/MTU mismatch
all routers stuck in 2-way state
check if all have priority 0
2-way is normal state between DROTHERs
router stuck in init state
has sent hellos, but can’t receive them
or cant receive neighbors’ router ID
What is an LSDB?
Link state database, contains LSAs for each link in the OSPF area. Knows router IDs, the cost, and network ID/prefix for each link.
The LSDB is identical for all routers in an area, different one for each area.
What does an LSA do?
Routers flood them to all neighbors until all routers in an OSPF area develop the same map of the network.
What information does an LSA contain?
the router ID of the sender
the cost of the link
the network address and prefix of the advertised link
How long do LSAs last?
Aging timer is 30 mins by default, LSA flooded again after expiration.
What is the backbone area?
area 0; all other areas must connect to it
What is the difference between an internal router, backbone router, and area border router?
Internal routers have all interfaces within a single area.
ABRs have interfaces in two or more areas.
Backbone routers are connected to the backbone area 0.
What command should you use on an OSPF router interface that has no OSPF neighbors?
Why?
(if)#passive-interface
It allows the router to send LSAs out of that interface, but prevents it from sending OSPF hello messages, saving bandwidth.
Difference between local route and connected route?
- local routes are host routes, /32. They represent an exit interface.
- connected route is an network route representing an adjacent link. /30.
creates a new LSA for the default route and floods it to all interfaces
default-information originate
be sure to remember that it is ‘information’ not ‘route’
How do you manually configure router ID, and what must you do afterwards to apply it to running config?
(config-router)# router-id 1.1.1.1
Afterwards use either:
reload command
clear ip ospf process (resets OSPF on the router, loses its routes)
What is an ASBR?
Difference between ABR?
Autonomous system boundary router - connects the OSPF network o an external network, usually originates the default gateway to internet.
Area Backbone router is just a router in the backbone area 0.
the OSPF network command does what?
specifies the interfaces to enable OSPF on, and what their area is
network 10.0.0.0 0.0.0.3 area 0
How do you configure router id for OSPF?
router-id 1.1.1.1
do not specify ospf
default reference bandwidth?
How do you change it?
100mbps
(config-router)# auto-cost reference-bandwidth 1000
how do you find the cost of an interface?
show ip ospf interface f0/0
ref/int = cost
(ospf after ip)
How do you calculate the cost of a route?
Sum of the cost of each exit interface along the path.
Cost of loopback interface?
1.
Add one whenever destination is a loop back interface even though it isn’t a real exit interface.
How do you manually configure cost, how does it interact with auto-cost reference-bandwidth?
ip ospf cost 100
it takes priority over auto calculated cost.
What is an alternative way to enable OSPF on an interface?
(if)# ip ospf 1 area 0
if you use this command, the “routing for networks” in show ip protocols will be absent, and display interfaces explicit instead.
What is similar about PPP and broadcast OSPF?
What is different?
They both have the same hello/dead timers, and can both dynamically discover neighbors.
PPP unlike broadcast does not elect DR/BDR.
why do DROTHERs have a max of only 2 adjacency?
DROTHERs can only become adjacent with DR and BDR, they stay neighbors with the other DROTHERs because they cannot progress past the 2-way state.
