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ICND2-Odom > External BGP > Flashcards

External BGP Flashcards

1
Q

What is the only Exterior Gateway protocol in use today?

A

BGP

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2
Q

What is meant by “reachability”

A

What prefixes are available?

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3
Q

Define NLRI

A

Network Layer Reachability information

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4
Q

What is the difference between and EGP and IGP

A

Exterior gateway protocols exchange routing information between autonomous systems. Interior gateway protocols exchange routing information within an autonomous system

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5
Q

What is the purpose of the ASN with regard to BGP?

A

Used for best path selection and loop prevention

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6
Q

What does BGP use in place of a metric?

A

Path Attributes

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7
Q

What is the purpose of the AS-PATH path attribute?

A

Lists ASNs in the route, on hop-by-hop basis

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8
Q

Describe a single-homed Internet Edge design

A

Single link connected to a single ISP

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9
Q

Describe a dual-homed Internet Edge design

A

Two or more links connected to a single ISP

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10
Q

Describe a multi-homed Internet Edge design

A

Connections to two or more ISPs, each by a single link

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11
Q

Describe a dual multi-homed Internet Edge design

A

Connections to two or more ISPs, each by two or more links for redundancy

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12
Q

What is meant by redistribution

A

advertising externally learned routes into the rest of an organization via an IGP

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13
Q

Does BGP have any concept of being enabled on an interface?

A

no

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14
Q

Does BGP have any concept of dynamically discovering neighbors?

A

No. Neighbors are pre-defined

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15
Q

BGP advertises about prefixes added to the BGP table. By what methods can prefixes be added to the BGP table?

A

via network statements
route redistribution
prefixes learned from peers

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16
Q

How does BGP exchange update messages

A

via TCP 179

17
Q

What command verifies that BGP peers are actively exchanging information?

A

show tcp brief

18
Q

What commands are used to configure BGP (generic answer—looking for basic config)

A

router bgp $my-asn
neighbor $neighbor_ip remote-as $their-asn
network $net-id [mask $subnet-mask]

19
Q

What can be verified by the command show ip bgp summary

A 
remote ASN
local ASN
Peer IP
Local RID
neighbor state
20
Q

How is the BGP router ID determined?

A

by explicit config (bgp router-id $RID)
highest loopback
highest working interface IP

21
Q

show ip bgp summary reveals a potential neighbor in the IDLE state. What can be inferred by this?

A

Neighbor’s bgp process in admin-disabled (shutdown)

22
Q

show ip bgp summary reveals a potential neighbor in the CONNECT state. What can be inferred by this?

A

Connection between peers is attempted, but no completed.

23
Q

show ip bgp summary reveals a potential neighbor in the ACTIVE state. What can be inferred by this?

A

Routers are connected, but no messages have been exchanged yet

24
Q

show ip bgp summary reveals a potential neighbor in the OPENSENT state. What can be inferred by this?

A

Router has sent the first message to establish a neighbor (peer) relationship, a BGPOPEN message

25
Q

show ip bgp summary reveals a potential neighbor in the OPENCONFIRM state. What can be inferred by this?

A

A full TCP connection exists between the two routers. The local router has received OPEN messages

26
Q

show ip bgp summary reveals a potential neighbor in the ESTABLISHED state. What can be inferred by this?

A

Routers are now peers and can exchange UPDATE messages

27
Q

Assume that a router has two connected networks, 192.0.2.0/29 and 192.0.2.128/26. The router is configured to advertise 192.0.2.0/24 via BGP. Will neighbor routers receive routes for the subnetted networks?

A

No. Routes configured for BGP advertisement are only added to the BGP table if a corresponding route exists in the routing table. Since a summary advertisement would be preferred, a static discard route for 192.0.2.0/24 should be created on the advertising router.

ip route 192.0.2.0 255.255.255.0 null0

28
Q

An ASN can be how many bits long?

A

16 or 32

29
Q

BGP is a routing protocol

A

path-vector

30
Q

When is it most appropriate to use BGP?

A

With multi-homed designs

ICND2-Odom (7 decks)

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