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CCNP BSCI Study
Preparation questions for BSCI exam
75
Computer Science
Professional
04/15/2009

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Term
In IPV6, what are the two types of autoconfiguration?
Definition

Stateless and Stateful

  • stateless involves a router sending an RA, or router advertisement with a prefix for that link and then the host attaching its MAC address to that to form the IPV6 address.
  • stateful simply uses an dhcp server, just like IPV4 does, to allocate addresses.  This is referred to as DHCPv6.
Term
What is the router command to enable IPV6 routing?
Definition
router (config)#ipv6 unicast-routing
Term
What versions of RIP, OSPF, IGRP, and BGP support IPV6?
Definition
Trick question.  With RIP it is RIPNG, with OSPF it is OSPFv3, with BGP it is BGPv4, but IGRP does not support IPV6.
Term

What are these IPV6 addresses?

  • 001
  • ::1
  • ::D190:4E71
  • 1111 1111
  • FF00::/8
  • 1111 1110 10
  • 1111 1110 11
Definition
  • 001 is a global unicast
  • ::1 is a loopback
  • ::D190:4E71 is an IPV4 compatible address where the first 96 bits are all zeroes.
  • 1111:1111 and FF00::/8 are both multicast
  • 1111 1110 10 is a link local address used primary on a link for neighbor discovery
  • 1111 1110 11 is a site local equivalent to IPV4 private addresses
Term
IPV6 summarization involves the use of a what?  It is equivalent to an IPV4 subnet.
Definition
Site Level Aggregate
Term
What IPV6 type of address can be used on several addresses at once?
Definition
An anycast address can be used on multiple devices but unlike a multicast that involves all the devices in the group receiving the data, the only device to get the data in an anycast group is the closest device.
Term

What are the IPV6 IPs for OSPF's multicast IPV4 addresses for all DR's and BDR's and all OSPF routers?

  • 224.0.0.5
  • 224.0.0.6
Definition

224.0.0.5 is FF02::5

224.0.0.6 is FF02::6

Term
When doing 6-to-4 tunneling with IPV4 and 6, what do the IPV6 addresses for edge routers look like?  What three parts will you always find in a 6-to-4 tunneling edge router ip?
Definition
An example would be 2002:1234:D1E4::/48.  They always start with 2002 then have the IPV4 address (expressed in HEX) with a /48 prefix. 
Term
What command starts the OSPF v3 IPV6 router process and what is unique about the router ID you need to configure under that process if there are no IPV4 addresses on the router?
Definition

router(config)#ipv6 router ospf 1

router(config-rtr)#router-id 1.1.1.1

 

If there are no IPV4 addresses on the router, you MUST create a router ID and you must use an IPV4 address-even if you don't have IPV4 address anywhere else on your network.

Term
What command puts an interface in OSPFv3 in an area?
Definition

router(config)#int f0/1

router(config-if)#ipv6 ospf 1 area 3

 

This will create a router process automatically.  In OSPFv2 you would put an interface in an area in global mode.

Term

What commands gives us this output?

[image]

Definition

show ipv6 ospf neighbor or show ip ospf neighbor

 

Both would give the same output.

Term
Given int f0/1 on a router with an ip address of 220.200.18.42, what commands would be needed to create an IPV6 6-to-4 tunnel on that interface?
Definition

rtr(config-if)#int tunnel 0

rtr(config-if)#ipv6 address 2002:DCC8:112A::/48

 

(need to first convert the IPV4 address to HEX and then create the tunnel interface and apply that new address)

 

Term

What show command would give you this output?

[image] 

 

Definition
show ipv6 ospf interface f0/1
Term
When looking at the OSPFv3 IPV6 routing table, what does the 'L' stand for?
Definition
A Local link on the same subnet.  Link local or Site Local.  (ie Private addressed link) 
Term
What are the two major types of BGP attributes for passing routing information?
Definition
well-known and optional which includes the well-known mandatory and well-known discretionary and the optional transitive and non-transitive.
Term
What are the BGP well-known mandatory attributes?
Definition
AS_Path, next-hop, and origin
Term
What are the well-known discretionary BGP attributes?
Definition
local preference and atomic aggregate
Term
What are the BGP optional transitive attributes?
Definition

aggregator

community

Term
What is the BGP optional non-transitive attribute which sounds like the opposite of what it does?
Definition
MED (multi-exit descriminator)
Term
Do BGP neighbors have to be directly connected?
Definition

No, but they do need to be able to reach each others IP address used to create the neighbor relationship.  This is done with the neighbor command under the BGP router process

rtr(config-router)#neighbor 1.1.1.1 remote-as 123

Term
What is the connection recommendation Cisco makes for eBGP neighbors compared to iBGP neighbors?
Definition
External BGP neighbors should be directly connected whereas internal neighbors do not have to be and usually are not.
Term
BGP neighbor relationships are reliable using what protocol and what port?
Definition
TCP 179
Term
What are the states that a BGP neighbor relationship goes through and what is a command to verify what state one is in?
Definition

Idle, Connect, Active, Open Sent, Open Confirm, and Established.

 

Show ip bgp neighbor

Term
Besides 'show ip bgp neighbor' what other command provides a great deal of info on bgp in general relating to the local router as well as listing the neighbors at the end of the output?
Definition
Show ip bgp summary.  This will list the neighbors at the bottom and tell you how long the connections have been up.
Term
What special command in BGP is necessary to create the neighbor relationship when the routers are not on the same subnet?
Definition

The bgp-multihop command.  Example,

rtr(config-router)#neighbor 1.1.1.1 ebgp-multihop 2

Term
If you choose to use the loopback address of the routers to create a neighbor relationship between two BGP peers what special command is necessary?
Definition
rtr(config-router)#neighbor 1.1.1.1 update-source loopback 1
Term
If you configure both routers with the correct neighbor command, the correct ebgp-multihop command, the correct update-source command (because you are using the loopback), and still the neighbor relationship will not come up, what might be the culprit?
Definition
In order for the neighbors to talk to each other they both must have a route in their respective route tables to each others loopback.  This can be solved with a quick static route.
Term
After entering 'show ip bgp' the BGP route table is displayed.  What does the *> symbols indicate?
Definition

* = valid

> = best route

 

Note: remember if you don't see the asterisk, the route is not usuable.

Term
What are the three possible path sources for routers in the BGP route table?
Definition

i = internal

e = external

? = incomplete, usually redistributed

Term

What is wrong with this config?

rtr(config)#int loopback 0

rtr(config-if)#ip address 3.3.3.3 255.255.255.0

rtr(config-if)#router bgp 100

rtr(config-router)#network 3.3.3.3 mask 255.255.255.255

 

Definition
The loopback with never show up in the route table as a valid path because the mask in the network command did not match the mask that the loopback was originally configured with.  They must match.
Term
In BGP what is the difference between an unrecognized optional transitive attribute and a non-transtitive?
Definition
 If the path is advertised to other routers and is transitive it will be sent to the other routers whether understood or not, whereas non-transitive routes that are unrecognized will NOT be passed on.
Term
List the first 6 BGP path selection criteria in order of importance
Definition

1. Highest Weight

2. Highest Local Preference

3. Whether it originated locally

4. Shortest AS_Path

5. Best origin code

6. Lowest MED

Term
T or F.  Cisco recommends running more than one OSPF process on Area Border Routers?
Definition
False.  They got enough tasking their cpu's without that.
Term
If you wanted to see if a route is accessible or not in BGP, what is a good command to check that?
Definition

Let's say the route is to 3.3.3.3 that we are concerned with.  Use the command 'show ip bgp 3.3.3.3' to see output that will tell if the route to that device is accessible or not.  Inaccessible routes will give this output:

[image] 

Term
An ebgp peer, router 3, sends an update to router 1 who in turn sends that update to router 2.  If router 2 does not have a route to router 3 how will it be able to talk to it?
Definition

Since router one originally learned the route from router 3, an ebgp peer, and then passed the update to an ibpg peer, router 2, router 1 needs to be the one to announce itself as the next hop.  So, this command would need to go on router 1 aimed at router 2:

rtr1(config-router)#neighbor 2.2.2.2 next-hop-self

Term
What is the purpose of the Multi-exit discriminator or MED in BGP? 
Definition

MED, the 6th criteria for path selection in BGP, is used to tell an ebgp neighbor the best path by which to ENTER an AS.   Which is odd since its name implies 'exiting' and not entering.  The MED can be set by way of a route map.  Here is one example of creating a route map to set the MED (or metric) to 200.  100 is the default.

 

rtr(config)#route-map MED permit 10

rtr(config-route-map)#match ip address 1

rtr(config-route-map)#set metric 200

The '1' in the second line is pointing to an access list you much create.

Term
The local_preference attribute is shared between ibgp and ebgp peers?
Definition
False.  It is local to an AS and it never leaves the AS.  Its purpose is to tell the local peers the best way to EXIT an AS in the event there is more than one path out.
Term
What command will change the local_preference sent out on every update on a router as a whole?
Definition
rtr(config-router)bgp default local-preference 200
Term
Weight, the first path selection attribute in BGP, is set to what on a route originated on a router?  And what is the value of all other routes?
Definition
32768 is the value for a route originated on the router and zero is the value of all the rest.  Weight is Cisco proprietary and is on significant on the local router and is not shared.
Term
What command can set the Weight value for a BGP router?
Definition

rtr(config)router bgp 100

rtr(config-router)#neighbor 2.2.2.2 weight 200

 

Term
On a bgp router if I had a loopback 0 with an IP of 1.1.1.1 255.255.255.0 and wanted to advertise that route, what command would do so?
Definition

rtr(config-router)#network 1.1.1.1 mask 255.255.255.0

or

rtr(config-router)#network 1.0.0.0 mask 255.0.0.0

Term
It is safe to turn off BGP synchronization if...
Definition

1.  All the routers in the AS are running BGP

2.  Your AS is a full mesh

3.  The AS is not a transit AS

 

You can turn if off with this command:

 

rtr(config-router)#no synchronization

Term
If router 1 is the be the route reflector in a BGP scenario with routers 2 and 3 being clients, what configuration is necessary to make this happen?
Definition

Only need to configure router 1, the reflector with these commands:

 

rtr1(config-router)neighbor 2.2.2.2 route-reflector-client

rtr1(config-router)neighbor 3.3.3.3 route-reflector-client

Term
In OSPF in order for routers to become neighbors they must agree on 3 things.  What are they?
Definition

1.  area number

2.  hello and dead timers

3.  stub flag

Term
In OSPF what is the Dykstra algorithm run against?
Definition
The Link-State Database
Term
OSPF's spf algorithm calculates a shortest path tree and that treee is used to come up with what?
Definition
The routing table
Term

Cisco recommends that an area in OSPF not contain more than.

a.  60 routers

b.  100 routers

c.  3 routers

d.  50 routers

Definition
d.  50 routers
Term
In OSPF routers have a priority of what by default, and what value will make the router ineligible for consideration in the DR/BDR selection process?
Definition
They are 1 by default and a 0 will take them out of the running to be a DR or BDR
Term
In OSPF if you wanted to set a router to a priority of 0 to eliminate its chance of becoming the DR or BDR, what command configured where will do this?
Definition

You would enter this command at the interface level:

 

rtr(config-if)ip ospf priority 0

Term
In the OSPF DR/BDR selection process if there is a tie with priorities, what is the tie breaker?
Definition

The router with the highest router ID, and here are the rules:

1.  The highest loopback interface is the first address looked at

2.  If not loopback, then the highest address on any physical address is considered

3.  Both of the above can be overridden if a manually configured router ID has been created with the 'router-id X.X.X.X' command under the OSPf routing process

Term
In OSPF if a network has a DR and it goes down and another is elected to that role, what happens when the original DR router comes back up?
Definition
Nothing.  There will not be a new DR election process.  The current DR and BDR would have to go down before this original DR router could be re-elected.  Even if it had a higher priority than the current DR.
Term
In OSPF if routers are on an ethernet segment, what will be the default network type and will a DR and BDR be elected?
Definition
The default type for an ethernet segment is 'Broadcast' and yes, a DR and BDR will be elected.
Term
What is a good command in an OSPF scenario to check the router-id, network type, hello and dead timers, cost associated with an interface on a router, and how many neighbors off that interface?
Definition

show ip ospf interface X/X

[image]

 

Term
In a non-broadcast OSPF network, like frame-relay, what is required on the hub router in order to create neighbor relationships with its neighboring routers?
Definition

The neighbor command will need to be used under the routing process for each neighbor.  Example:

rtr(config-router)#neighbor 2.2.2.2

This command will not be needed on the spoke routers

Term
In an OSPF NBMA network do you need to statically configure neighbors?  Or are they automatically found?
Definition
They are not found automatically and will have to be configured with the 'neighbor x.x.x.x' command on the hub router only.
Term

The hello and dead timers on a broadcast OSPF network, like ethernet, is 30 and 120 respectively.

 

T  or  F

Definition
False.  It is 10 and 40.  It is 30 and 120 on a frame-relay NBMA network though.
Term
In an OSPF scenario what network type do serial interfaces default to?
Definition

NBMA, but it can be changed with the 'ip ospf network XXXXX' command. The four choices are:

broadcast

non-broadcast

point-to-multipoint

point-to-point

Term
When configuring an interface as an OSPF network type of point-to-multipoint with the 'ip ospf network' command , what are your two options?
Definition

If you don't put anything it will default to broadcast, but you can make it nonbroadcast with the 'nonbroadcast' parameter.

 

rtr(config-if)ip ospf network point-to-multipoint non-broadcast

Just remember that if you choose non-broadcast you will have to statically configure neighbors

Term

What two network types in OSPF are RFC compliant from this list:

NBMA

point-to-multipoint

broadcast

point-to-point

point-to-multipoint nonbroadcast

Definition

NBMA and point-to-multipoint

 

The others are not officially compliant but can be used over a NBMA network.

Term
When created a virual link in OSPF, what are three possible reasons it might not work after attempting to create the link?
Definition

1.  Used wrong IP in command.  Have to use the remote routers RID

2.  Forgot to configure authentification when area 0 is doing it

3.  Tried to use a stub area as the transit area

Term
What is the syntax of the command to create an OSPF virtual link if the remote router's RID is 2.2.2.2 and the transit area is area 34?
Definition
rtr(config-router)#area 34 virtual-link 2.2.2.2
Term

The OSPF command to create a virtual link is entered in what router config mode?

 

Global, interface, or router

Definition
(config-router)
Term
What command will tell you how many times the SPF algorithm has been run in an OSPF scenario?
Definition
show ip ospf
Term
Using multiple areas,instead of one big area 0, in OSPF is recommended because it will do what?
Definition
Reduce overhead on the router, reduce the number of LSA's being sent into any one area, and thus reduce the number of SPF recalculations being done in each area
Term
What is the formula to determine cost of an interface in OSPF?
Definition
100million/BW in BPS
Term
In an OSPF network what is the default cost assigned a serial interface?
Definition

64.  Others are:

 

Ethernet          10

FastEthernet      1

56k circuit     1785

Term
OSPF updates happen whenever there is a change in the network topology or ever _____  minutes.
Definition
30
Term

What are OSPF's 8 stages to neighbor adjacency?

 

Definition

1.  Down

2.  Attempt - hello packets sent

3.  Init - hello packet received

4.  2-Way - hello received with each router's own RID meaning 2-way communication is established

5.  Exstart - DR/BDR election and master/slave relationship set up and databases starting to be shared

6.  Exchange - DBD packets exchanges with Link State Database info

7.  Loading - sending of LSR's to each other

8.  Full - each router's Link State Database are synchronized with each other

Term
In an OSPF ethernet network with four routers on the network will all of the routers form adjacencies with each other?
Definition
NO.   A DR and a BDR will be elected and then the remaining two routers will form adjacencies only with the DR's, and not with each other.  The two Drothers, the non-DR routers, will never get past 2-way with each other.  This is to help keep down the number of LSA's being sent.
Term
In OSPF, what network types elect DR's and BDR's?
Definition
broadcast
Term
What OSPF command can override priorities of routers and thus affect the DR election process?
Definition
Priority.  The 'ip ospf priority X' command can affect who can and cannot be elected DR or BDR.
Term
What command will tell you if a router is an ABR or ASBR in and OSPF scenario?
Definition
show ip ospf
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