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OSPF Labs (Base config, DR/BDR, Metric, Passive, Timers)
Terms in this set (11)
What are the three steps in OSPF base configuration? [PRN]
1) OSPF process ID
...#router ospf 1#
...Does not designate OSPF area, only the local process, can be the same for all OSPF routers
3) Networks to advertise (command will also send out neighbor requests through the interface)
...#network 10.1.3.0 0.0.0.255 area 0
...#network 10.1.3.1 0.0.0.0 area 0 (best practice, enable OSPF on interface)
What are the four loading states to OSPF full neighbor relationship? [EELF]
1) EXSTART (master-slave negotiation, DBD packets)
2) EXCHANGE (LSR and LSU communication)
3) LOADING (process all updates)
4) FULL (full relationship reached)
How does an OSPF router know when to try and elect a DR/BDR on a segment?
1) The network type that an interface is connected to (broadcast [Ethernet], point-to-point) determines this
...#sh ip ospf interface# will show network type
How would you manually assign a DR/BDR and keep it that way even if it reloads?
1) Manually assign a DR by using #ip ospf priority 10#
2) Exclude other OSPF routers on the segment from the DR/BDR election by changing their priority to 0
What metric does OSPF use and what is the formula for calculating it?
1) OSPF metric is known as COST
2) COST = 100 / (bandwidth in Mbps)
What is the command to change reference bandwidth and why would you want to change it from the default?
1) #auto-cost reference-bandwidth 1000# changes the divisor bandwidth in the metric formula to account for 1Gb, 10Gb, 40Gb interface speeds since OSPF does not count decimals in the values for COST
How can you manually change the COST of an interface?
1) #ip ospf cost x#
2) Not recommended
How would you prevent MITM attacks on an OSPF network?
1) Security best practice is to prevent OSPF neighbors from forming on non-necessary segments to prevent MITM attacks by enabling passive interfaces
2) You can also implement OSPF authentication to prevent MITM
What options are there to implement passive interfaces on an OSPF network?
1) Enable passive configuration per interface
...#sh ip ospf interface# to verify
2) Enable passive configuration for all interfaces
...#no passive-interface f0/0#
How would you adjust hello timers to detect network failures faster and what will OSPF automatically update once the hello timer is changed?
1) int#ip ospf hello-interval 1#
2) OSPF will automatically change the dead timer to four times the hello timer
How are loopback interfaces used with OSPF?
1) You can assign a loopback interface the OSPF router-ID and then advertise that interface into the OSPF network to verify connectivity
THIS SET IS OFTEN IN FOLDERS WITH...
IOS Images and Licensing
Point-to-Point Connections and WAN Technologies
Understanding and Configuring BGP
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