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CCNP Core > Chap 12 - Advanced BGP (part 1) > Flashcards

Chap 12 - Advanced BGP (part 1) Flashcards

1
Q

What is BGP’s default behavior when multihoming?

A

To install only the best path to the RIB which means only one path for a network prefix is used when forwarding network traffic to a destination.

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2
Q

What are 3 factors an organization considers when choosing a second service provider?

A
  • Cost
  • Circuit availability for remote locations
  • Separation of the control plane
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3
Q

What’s the risk of using more than one service provider?

A

The organization’s AS might become a Transit AS.

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4
Q

How can transit routing be avoided?

A

By applying outbound BGP route policies that only allow for local BGP routes to be advertised to other AS’s.

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5
Q

How can transit routing be avoided at branch sites?

A

Configure route filtering at each branch so that branch sites do not advertise what they learn from the WAN.

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6
Q

If transit routing is to be used what are 4 restrictions?

A
  • Data Centers
  • Proper routing design accomodates outages
  • Bandwidth is sized accordingly
  • The routing pattern is bi-directional and predictable
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7
Q

How do Standard ACLs define packets?

A

Based on the source network only.

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8
Q

What 5 things can Extended ACLs filter on?

A
  • Source
  • Destination
  • Protocol
  • Port
  • Other packet attributes
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9
Q

How are Standard ACLs identified?

A
  • Range 1 to 99
  • Range 1300 to 1999
  • Named
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10
Q

How are Extended ACLs identified?

A
  • Range 100 to 199
  • Range 2000 to 2699
  • Named
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11
Q

What are the 2 parts that a prefix match specification contains?

A
  • High order bit pattern (network)
  • High order bit count (mask)
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12
Q

What does the following prefix match? 10.168.0.0/13 ge 24

A
  • Bit count is 13
  • Bit pattern has to match the first 13 bits of 10.168.0.0
  • First octet must be 10.
  • First 5 bits of the second octet must be binary 10101 to match 168
  • Network mask has to be /24 or greater
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13
Q

What is the regex to start a string?

A

^ Caret

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14
Q

What is the regex to end a string?

A

$ Dollar sign

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15
Q

What is the regex to match a space.

A

_ Underscore

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16
Q

What is the regex to match a single character?

A

[] Match whatever character is inside the brackets

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17
Q

What are the 4 components of a route map?

A
  • Sequence number
  • Conditional matching criteria
  • Processing action
  • Optional action
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18
Q

In a route map what is the Conditional Matching Criteria

A

Identifies prefix characteristics like network, BGP Path Attribute, next hop, etc.

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19
Q

In a route map what is the Processing action?

A

Permit or Deny

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20
Q

In a route map what is Optional Action?

A

Can include modification, addition, or removal of route characteristics

21
Q

What are 6 Match Options for a route map?

A
  • match as-path (acl)
  • match ip address
  • match ip address prefix-list (prefix_list)
  • match local-preference (local_pref)
  • match metric (metric)
  • match tag (tag)
22
Q

In a route map with multiple Match Variables how many variables must match for the prefix to qualify?

A

Only one

23
Q

In a route map with multiple Match Options ( statements ) how many must be met for the prefix to qualify?

A

All of them.

24
Q

In route maps what are 7 Optional Actions?

A
  • set as-path prepend
  • set ip next-hop
  • set local-preference
  • set metric
  • set origin
  • set tag
  • set weight
25
Q

In a route map with multiple sequences by default how are they processed?

A

Route map processing stops when the first sequence has been matched.

26
Q

In a route map what does the keyword ‘continue’ do?

A

It allows the route map to continue processing even if there has been a match.

27
Q

When are inbound route policies executed?

A

Inbound route policies are executed when the route is in the Adj-RIB-in and before it gets to the Loc-RIB table.

28
Q

When are outbound route policies executed?

A

Outbound route policies are executed before the route gets to the Adj-RIB-out.

29
Q

What are 4 methods of filtering routes inbound or outbound?

A
  • Distribute list
  • Prefix list
  • AS Path ACL filtering
  • Route maps
30
Q

What does a Distribute List do?

A
  • Prefixes are filtered based on an ACL.
  • Has an implicit deny.
31
Q

What is a Prefix List?

A
  • A prefix list is a list of prefix-matching specifications permitting or denying processed in a top down fashion.
  • Has an implicit deny
32
Q

What is an AS Path ACL and what numbering range does it have?

A
  • It’s a list of regex commands that permit or deny based on the current AS-Path value.
  • Has an implicit deny
  • 1 - 500
33
Q

What do Route Maps do?

A

Conditional matching on a variety of prefix attributes and taking a variety of actions.

34
Q

Can a BGP neighbor use a distribute list and a prefix list at the same time?

A

No

35
Q

What are two methods of clearing BGP connections?

A
  • Hard reset - tears down the BGP session, removes routes from peer, the most disruptive
  • Soft reset - invalidates BGP cache, request a fully advertisement from peer
36
Q

What are BGP Communities?

A
  • 32-bit field used for tagging routes or modifying routing policy on upstream or downstream routers
  • Optional Transitive BGP Attribute
  • Traverses from AS to AS
37
Q

What are 3 well-known Communities?

A
  • Internet - identifies routes that should be advertised on the Internet
  • No_Advertise - don’t advertise to any BGP peer
  • No_Export - only advertise to iBGP peers
38
Q

What range of numbers are used for Standard Community Lists?

A

1 to 99

39
Q

What range of numbers are used for Extended Community Lists?

A

100 to 500

40
Q

What is the difference between a Standard Community List and an Extended Community List?

A
  • Standard Community Lists match on well-known communities or private communities.
  • Extended Community Lists match using regex commands
41
Q

For BGP Communities what is the ‘new format’ and how many bits for each number?

A

Two 16 bit numbers as in 100:12345

42
Q

Do IOS router display Communities by default?

A

No

43
Q

What is the format for a Private BGP Community?

A

AS number separated with a colon followed by a number assigned by the AS.

44
Q

What is the command that will change the display of a Community to the new format?

A

ip bgp community new-format

45
Q

What 4 events cause BGP to calculate a new best path?

A
  • BGP next-hop reachability change
  • Failure of an interface that connects to BGP peer
  • Redistribution change
  • Reception of a new or removed paths for a route.
46
Q

What is the first thing BGP looks at when calculating the best path?

A

Longest match ( /25 would be preferred over a /24)

47
Q

Display the current BGP table, based on routes that meet a specified AS path regex pattern

A

show ipv4 unicast bgp regexp

48
Q

Display the current BGP table, based on routes that meet a specified BGP community

A

show bgp community

49
Q

What are the number ranges for standard and extended community lists?

A
  • Standard is 1 - 99
  • Extended is 100 - 500

CCNP Core (46 decks)

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