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IP Engineering > Week 10: BGP > Flashcards

Week 10: BGP Flashcards

1
Q

What are the two types of Routing?

A
  • Interior Gateway Protocol (IGP)

- Exterior Gateway Protocol (EGP)

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2
Q

Where are IGP’s used?

A

Within autonomous systems

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3
Q

What are examples of IGP’s?

A
  • RIP
  • OSPF
  • IS-IS
  • EIGRP
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4
Q

Where are EGP’s used?

A

Between Autonomous Systems

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5
Q

What are some examples of EGP’s?

A
  • BGP
  • EGP
  • ISO’s IDRP
  • Novell’s NLSP
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6
Q

Why do we need BGP?

A
  • Single public IP + NAT/PAT
  • Redundancy
  • Multihoming
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7
Q

What is BGP?

A

A popular Exterior Gateway Path Vector Protocol

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8
Q

What is unique about BGP?

A

BGP forms neighbour relationships before sending routing information

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9
Q

What does BGP do when it forms neighbour relationships for transmitting routing information?

A
  • Neighbour IP address is explicitly configured & maye not be on the same subnet
  • Uses TCP connection b/w neighbours
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10
Q

What port does BGP use for the TCP connection between neighbours?

A

Port 179

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11
Q

What list does BGP use to route a packet?

A

The list of Autonomous Systems

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12
Q

What is the list of Autonomous Systems that are associated with a BGP route called?

A

AS_PATH

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13
Q

True or False: BGP doesn’t rely on neighbours to pass along routes from their routing tables

A

False, BGP relies on neighbours to pass along routes from their routing tables

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14
Q

what is the AS_PATH attribute?

A

A list of traversed Autonomous Systems?

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15
Q

How does BGP determine the shortest inter-AS path?

A

From a list of numbers known as the AS_PATH attribute

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16
Q

What is the metric used by BGP?

A

Hop Count

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17
Q

True or False: BGP uses a different metric than Hop Count for loop avoidance?

A

False, BGP uses Hop Count as a metric & a Loop Avoidance Device

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18
Q

What is an Autonomous System (A.S.)?

A

A collection of networks under a single Administrative Domain

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19
Q

How many bits long are Autonomous System Numbers?

A

16 bit

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20
Q

What is the bit range for Globally Unique A.S. Numbers?

A

1 - 64,511

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21
Q

What is the bit range for Private A.S. Numbers?

A

64, 512 - 65,535

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22
Q

What is a Stub A.S.?

A

An A.S. where all packets coming from it are originated in it

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23
Q

What is a Transit A.S.?

A

An A.S. that forwards incoming packets to their destination en-route

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24
Q

What is a Multihomed A.S.?

A

An A.S. with more than one external connection

25
Q

True or False: A Transit A.S. doesn’t have to by multihomed for packet transit

A

False, A Transit A.S. must by multihomed by definition for a packet to transit the A.S.

26
Q

What are the two types of Peering Relationships?

A

User/Customer Peering

Private Peering

27
Q

What is Use/Customer Peering?

A

Using Transit A.S. to get to other networks

28
Q

What is Private Peering?

A

Service providers agree to share routes

29
Q

Where do Public Peering connections take place?

A

At well-known Internet Exchange Points (IXP)

30
Q

What is an Internet Exchange Point?

A

A physical location through which Internet infrastructure companies (ISP’s) & CDN’s connect with each other

31
Q

What are the two types of BGP?

A

Internal & External

32
Q

What is External BGP (EBGP)?

A

A BGP session established between two neighbours in different Autonomous Systems

33
Q

What is Internal BGP (IBGP)?

A

A BGP session that is established between two neighbours in the same AS

34
Q

What is the sequence of operations for BGP?

A
  • Establish session on TCP Port 179
  • Exchange all active routes
  • Exchange incremental updates
35
Q

What are the 4 types of BGP packets that are exchanged during operation?

A
  • Open
  • Notification
  • Update
  • Keepalive
36
Q

What is the function of Open BGP Message Type?

A

Establish a peering session

  • Announces A.S. of of the originating router
  • Determine hold timer interval
37
Q

What is the function of a Keep_Alive BGP Message Type?

A

Handshake at regular intervals

38
Q

What is function of a Notification BGP Message Type?

A

Shuts down a peering session

39
Q

What is the function of an Update BGP Message Type?

A

Announcing new routes or withdrawing previously announced routes

40
Q

What is the Open BGP Message Type used for?

A
  • Announcing A.S. of the originating router

- Determines holddown timer interval between keep_alive or update messages (0 implies no keep_alive)

41
Q

What is the keep_alive BGP message type used for?

A
  • Sent periodically (but before hold timer expires) to peers to ensure connectivity
  • Send in place of an UPDATE message
42
Q

What is the Notification Message Type used for?

A
  • Error Notification

- TCP Conncetion is closed immediately after notification

43
Q

What is the Update BGP Message Type used for?

A
  • NLRI (Network Layer Reachability Information)
  • Path Attributes
  • Withdrawn Routes
44
Q

What is Policy Based Routing (PBR)?

A

Access control is placed on some routes

45
Q

What is Policy Based Routing used for?

A
  • Avoid transit situations

- Enforce national laws/security concerns/content issues

46
Q

True or False: BGP doesn’t provide the capability for enforcing various policies

A

False, BGP provides capability for enforcing various policies

47
Q

True or False: Policies are part of BGP

A

False, Policies are not part of the BGP Protocol, they are provided to BGP as config information

48
Q

How does BGP enforce policies?

A

By choosing paths from multiple alternatives & controlling advertisement to other A.S.’s

49
Q

List some examples of BGP Policies

A
  • A multi-homed A.S. refuses to act as transit
  • A multi-homed A.S. can become transit for some A.S.’s
  • An A.S. can favour of disfavour certain A.S.’s for traffic transit from itself
  • A.S can enforce national laws or security concerns or content issues
50
Q

What are the BGP Path Attributes?

A
  • Origin
  • AS_PATH
  • NEXT_HOP
51
Q

What is a BGP Path Attribute?

A

A characteristic of an advertised BGP route

52
Q

what are the Types of BGP Path Attributes?

A
  • Well-known Mandatory
  • Well-Known Discretionary
  • Optional Transitive
  • Optional Nontransitive
53
Q

What are some Well-Known Mandatory BGP Path Attributes?

A
  • ORIGIN
  • AS_PATH
  • NEXT_HOP
54
Q

What are some Well-Known Discretionary BGP Path Attributes?

A
  • LOCAL_PREF

- ATOMIC_AGGREGATE

55
Q

What is an Optional Transitive BGP Path Attributes?

A

AGGREGATOR

56
Q

What is an Optional Nontransitive BGP Path Attribute?

A
  • MULTI_EXIT_DISC

- ORIGINATOR_ID

57
Q

True or False: LOCAL_PREF is used externally to an A.S. to tell routers which path to take

A

False, LOCAL_PREF is used locally within an A.S. to tell routers which exit path to take out from an A.S.

58
Q

True or False: LOCAL_PREF selects the lowest local preference

A

False, LOCAL_PREF selects the highest local preference

59
Q

True or False: local preference is advertised between eBGP and iBGP peers

A

False, local preference is only advertised between iBGP peers

LOCAL_PREF attribute is never advertised outside of an A.S.

IP Engineering (15 decks)

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