Ccnp Route, Chapter 18- Bgp Attributes And Path Selection

Front 1

IGPs choose a path based on things like _____________

Back 1

• Bandwidth
• Delay
• Hop Count
• etc

Front 2

BGP Chooses a path based on ______________

Back 2

Policy

Front 3

How many paths per destination does BGP Choose?

Back 3

One

Front 4

What is BGP metric?

Back 4

BGP atributes

Front 5

What is BGP attribute priority 1?

Back 5

Weight (highest)

Front 6

What is BGP attribute priority 2?

Back 6

Local Preference (highest)

Front 7

What is BGP attribute priority 3?

Back 7

Originate (Local Originate)

Front 8

What is BGP attribute priority 4?

Back 8

AS Path (shortest)

Front 9

What is BGP attribute priority 5?

Back 9

Origin Code (IGP < EGP < Incomplete)

Front 10

What is BGP attribute Priority 6?

Back 10

MED (lowest)

Front 11

What is BGP attribute Priority 7?

Back 11

Paths (external preferred over internal)

Front 12

What is BGP attribute Priority 8?

Back 12

Router ID (lowest)

Front 13

In BGP there are multiple paths stored in a routing table to get to a destination how many will be in the routing table ?

Back 13

only one in the routing table

Front 14

What decisions can be made about the attribute weight?

Back 14

If there is a different in weight then we can make a decision and choose the BGP path with the best weight.

Front 15

If the weight attribute is equal what happens?

Back 15

If the weight is equal than we move down to local preference (priority 2)

Front 16

If one path has a better local preference what do you do?

Back 16

We will choose the path with the better local preference.

NOTE:
If the local preference is the same move to priority 3 (originate)

Front 17

If BGP attributes 1-6 are all equal how is a router chosen?

Back 17

A router with a router ID is chosen and placed in the routing table.

Front 18

What priority is BGP Attribute Weight?

Back 18

Priority 1

Front 19

What priority is BGP Attribute local preference?

Back 19

Priority 2

Front 20

What priority is BGP Attribute Orignate?

Back 20

Priority 3

Front 21

What priority is BGP Attribute AS Path?

Back 21

Priority 4

Front 22

What priority is BGP Attribute Origin Code?

Back 22

Priority 5

Front 23

What priority is BGP Attribute Med?

Back 23

Priority 6

Front 24

What priority is BGP Attribute Paths?

Back 24

Priority 7

Front 25

What priority is BGP Attribute Router ID?

Back 25

Priority 8

Front 26

Weight is only ____________ on the router?

Back 26

Local

Front 27

The path with the __________ weight is preferred?

Back 27

Highest Weight

Front 28

How would you change the weight of a neighbor?

Back 28

neighbor (IP Address of neighbor) weight (AnyNumber)

Front 29

What can you use local preference (priority 2) for?

Back 29

To chose the outbound external BGP path.

Front 30

Local preference is sent to___________________ routers in your AS.

Back 30

all internal BGP Routers in your AS

Front 31

Local preference is _____ between external routers

Back 31

Not Exchanged between external routers

Front 32

What is the default value for local preference?

Back 32

100

Front 33

The path with the __________ local preference is preferred.

Back 33

Highest

Front 34

Local Preference is configured to __________

Back 34

select an exit point.

Front 35

A well-known _____________ BGP attribute must be recognized by all BGP routers per RFC but its presence in a BGP update is optional.

Back 35

Discretionary

Front 36

How do you change the default local preference?

Back 36

"bgp default local-preference" command

Front 37

If the weight and local preference are the same than ______________ attribute will kick in

Back 37

3rd

originate

Front 38

BGB prefers the _____ AS path to get to the destination.

Back 38

Shortest Path

NOTE:

Less is Better

Front 39

How can we manipulate the AS Path?

Back 39

AS Path prepending

Front 40

What is AS path prepending command?

Back 40

This is influencing the routing AS Path.

Front 41

What does "set as-path-prepend" command do?

Back 41

Allows you to add you AS path number multiple times

Front 42

What are the 3 origin codes you could see in the bgp table

Back 42

• i = IGP
• e = EGP
• ? = Incomplete

Front 43

If you use the network command what origin code will you see?

Back 43

i

NOTE:

It means you advertised the network yourself in BGP. EGP is historical and is not used any more.

Front 44

If you see an i for the origin code in BGP table what does that mean?

Back 44

You have redistributed something into BGP

Front 45

What does Med mean?

Back 45

Metric

Front 46

How is med used?

Back 46

Med is used to advertise to your neighbors how they should enter your AS

Front 47

MED is exchanged between _______________

Back 47

Autonomous systems

Front 48

MED is propageted to all routers within th neighbor AS but is not _________

Back 48

passed along any other AS

Front 49

What kind of paths does the 7th BGP attribute (paths) prefer?

Back 49

BGP will prefer external (EBGP) over interal paths (IBGP).

NOTE:

You rarely make it this far because normally we already made a decision because of weight, local preference, AS paths or the MED

Front 50

What is the last BGP attribute?

Back 50

Router ID