Exam Prep - CCNA > FreeForm-2 > Flashcards

FreeForm-2 Flashcards

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1
Q

What is BGP?

A

BGP (Border Gateway Protocol) is the de facto inter-domain routing protocol used to exchange routing information between autonomous systems (ASes).

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2
Q

What is the purpose of AS-path in BGP?

A

BGP uses AS-path information to prevent routing loops.

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3
Q

Where is BGP defined?

A

BGP is defined in RFC 4271 and operates over TCP port 179.

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4
Q

What is an Autonomous System Number (ASN)?

A

An ASN uniquely identifies each AS; public ASNs range from 1–64511.

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5
Q

What is the difference between eBGP and iBGP?

A

eBGP is used between ASes; iBGP is used within the same AS.

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6
Q

What attributes does BGP use for route selection?

A

BGP selects the best path using attributes like Weight, Local Preference, AS Path, Origin, MED, eBGP over iBGP, and Router ID.

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7
Q

What is Weight in BGP?

A

Weight is Cisco-specific and highest wins (local to router).

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8
Q

What is Local Preference in BGP?

A

Local Preference is AS-wide; higher is preferred.

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9
Q

How does BGP prefer AS Path?

A

Shorter paths are preferred.

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10
Q

What is Multi-Exit Discriminator (MED)?

A

MED is lower is better; used to influence inbound traffic.

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11
Q

What are the types of BGP messages?

A

BGP message types include OPEN, UPDATE, KEEPALIVE, and NOTIFICATION.

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12
Q

What does the OPEN message do?

A

The OPEN message establishes a BGP session.

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13
Q

What does the UPDATE message do?

A

The UPDATE message advertises or withdraws routes.

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14
Q

What does the KEEPALIVE message do?

A

The KEEPALIVE message maintains session liveliness.

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15
Q

What does the NOTIFICATION message do?

A

The NOTIFICATION message signals errors and tears down the session.

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16
Q

What are Well-Known Mandatory BGP attributes?

A

Well-Known Mandatory attributes include AS_PATH, NEXT_HOP, ORIGIN.

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17
Q

What are Well-Known Discretionary BGP attributes?

A

Well-Known Discretionary attribute is LOCAL_PREF.

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18
Q

What are Optional Transitive BGP attributes?

A

Optional Transitive attributes include COMMUNITY, AGGREGATOR.

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19
Q

What are Optional Non-Transitive BGP attributes?

A

Optional Non-Transitive attributes include MED, ORIGINATOR_ID.

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20
Q

What is route dampening in BGP?

A

Route dampening suppresses flapping routes.

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21
Q

What is prefix filtering in BGP?

A

Prefix filtering prevents route leaks and hijacks.

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22
Q

What is BGP TTL Security (GTSM)?

A

BGP TTL Security (GTSM) mitigates spoofed eBGP sessions.

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23
Q

What is MD5 authentication in BGP?

A

MD5 authentication secures BGP sessions (though now deprecated in favor of TCP-AO).

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24
Q

What is required for full mesh iBGP?

Study These Flashcards
A

Full mesh iBGP is required unless using route reflectors or confederations.

25
What do Route Reflectors (RRs) do?
Route Reflectors reduce iBGP mesh complexity by reflecting routes to clients.
26
What are confederations in BGP?
Confederations divide an AS into sub-ASes to scale iBGP.
27
What are BGP communities?
BGP communities tag routes for policy control and filtering.
28
How can BGP peering be established?
BGP peering can be established over physical or loopback interfaces (loopback preferred for iBGP).
29
What commands are used for BGP troubleshooting?
Use show ip bgp, show ip bgp summary, and debug ip bgp for diagnostics.
30
What are the BGP session states?
BGP session states are Idle → Connect → Active → OpenSent → OpenConfirm → Established.
31
How does BGP convergence compare to IGPs?
BGP convergence is slower than IGPs; tuning timers and fast-external-fallover can help.
32
What is soft reconfiguration in BGP?
Soft reconfiguration allows inbound policy changes without resetting the session.
33
What are route maps and prefix lists used for in BGP?
Route maps and prefix lists are essential for granular control of route advertisement and acceptance.
34
What does STP (IEEE 802.1D) do?
STP prevents Layer 2 loops by creating a loop-free logical topology.
35
How is the Root Bridge elected in STP?
Root Bridge Election is based on the lowest Bridge ID (priority + MAC address).
36
What are Bridge Protocol Data Units (BPDUs)?
BPDUs are exchanged to share topology information.
37
What are the Port Roles in STP?
Port Roles include Root Port, Designated Port, and Non-Designated (Blocking) Port.
38
What are the Port States in STP?
Port States: Blocking → Listening → Learning → Forwarding → Disabled.
39
What is Rapid STP (RSTP)?
RSTP improves convergence time to <6 seconds.
40
What is Multiple STP (MSTP)?
MSTP maps multiple VLANs to a single STP instance.
41
What is Per-VLAN STP (PVST+)?
PVST+ runs a separate STP instance per VLAN (Cisco proprietary).
42
What is Rapid PVST+?
Rapid PVST+ combines RSTP speed with PVST+ VLAN granularity.
43
What does BPDU Guard do?
BPDU Guard disables a port if a BPDU is received on a PortFast-enabled port.
44
What is the Root Port in STP?
Root Port is the port with the lowest path cost to the Root Bridge.
45
What is a Designated Port?
Designated Port is the best forwarding port on a segment.
46
How is Path Cost determined?
Path Cost is inversely proportional to link speed (e.g., 100 Mbps = cost 19).
47
What are the tiebreakers for equal-cost paths?
Tiebreakers: lowest sender BID → lowest port priority → lowest port number.
48
What are Topology Change Notification (TCN) BPDUs?
TCN BPDUs are sent when a port goes up/down.
49
What does PortFast do?
PortFast skips Listening/Learning states for edge ports (e.g., hosts).
50
What is UplinkFast?
UplinkFast accelerates convergence for access-layer switches with redundant uplinks.
51
What does BackboneFast do?
BackboneFast speeds up convergence when indirect link failures occur.
52
What does Loop Guard do?
Loop Guard prevents alternate ports from becoming designated due to missing BPDUs.
53
What does Root Guard do?
Root Guard prevents a port from becoming a Root Port if a superior BPDU is received.
54
What is a design tip for STP?
Always manually set Root Bridge priority to control topology (default is 32768).
55
How can you verify STP configurations?
Use show spanning-tree to verify port roles, root bridge, and path costs.
56
What can cause interoperability issues in STP?
Mismatch in STP versions (e.g., PVST+ vs MSTP) can cause interoperability issues.
57
What does BPDU Filtering do?
BPDU Filtering suppresses BPDU transmission/reception—use with caution.
58
What triggers STP recalculation?
STP recalculation is triggered by topology changes, VLAN changes, or link failures.
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