CCNA 200-301
Last-Minute Power Sheet
Straight to the exam hotspots — practical, readable, and easy to review quickly.
How to use this sheet
Focus on the bold numbers, command syntax, packet types, and decision rules. The goal is quick recall
rather than long explanations.
Straight to the exam hotspots – no filler, just the stuff that actually shows up
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1. ROUTING PROTOCOLS – OSPF vs EIGRP Head‑to‑Head
The Big Comparison
Feature OSPF EIGRP
Type Link‑state Advanced distance‑vector
Algorithm Dijkstra SPF DUAL (Diffusing Update Algorithm)
Vendor Open standard (RFC 2328) Cisco‑proprietary (now RFC 7868
informational)
Default AD 110 90 (internal) / 170 (external)
Metric Cost (based on bandwidth) Composite (bandwidth + delay by
default)
Convergence 5‑40 sec (untuned) Very fast (if feasible successor exists)
Exam weight Heavy (~10‑12 questions) Moderate (~4‑6)
What they test Neighbor states, DR/BDR, LSA types, Basic config, K‑values, successor/FS
areas
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Administrative Distance – Memorize This Order
Lower AD = more trusted. When two protocols know the same route, the lowest AD wins.
Route Source AD
Connected 0
Static 1
EIGRP (internal) 90
OSPF 110
IS‑IS 115
RIP 120
EIGRP (external) 170
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CCNA 200-301 • Last-Minute Power Sheet Page 1
, OSPF Metric Calculation – The Formula You Must Know
Cost = Reference bandwidth ÷ Interface bandwidth (rounded up, min 1)
Default reference bandwidth = 100 Mbps
Interface Speed Default Cost Gotcha
10 Mbps 10 —
100 Mbps (FastEthernet) 1 —
1 Gbps 1 ️ Same as 100M!
10 Gbps 1 ️ Same as 100M!
Exam trap: With the default reference, OSPF can't tell 100M from 10G – they all cost 1. Fix it
with:
auto-cost reference-bandwidth 10000 (sets reference to 10 Gbps)
OSPF runs directly over IP – protocol number 89
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EIGRP Metric – Quick Facts
• Default K‑values: K1=1, K3=1, others = 0 → Metric = bandwidth + delay
• Neighbor requirements: Same AS number AND matching K‑values
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OSPF Neighbor States – The Sequence You'll See on the Exam
DOWN → INIT → 2WAY → EXSTART → EXCHANGE → LOADING → FULL
State What’s Happening
DOWN No Hello received
INIT Hello received, but didn't see own Router ID
2WAY Bi‑directional communication established (DR/BDR
election happens here)
EXSTART Ready to exchange Database Descriptors (DBD)
EXCHANGE Swapping DBD packets
LOADING Requesting missing LSAs (sending LSRs)
FULL Adjacency complete!
OSPF multicast addresses:
• 224.0.0.5 – all OSPF routers
• 224.0.0.6 – DR/BDR only
---
OSPF Packet Types – The 5 Brothers
Type Name Purpose
1 Hello Discover and maintain neighbors
2 DBD (Database Description) Summarize LSDB contents
3 LSR (Link‑State Request) Ask for specific LSAs
CCNA 200-301 • Last-Minute Power Sheet Page 2
Last-Minute Power Sheet
Straight to the exam hotspots — practical, readable, and easy to review quickly.
How to use this sheet
Focus on the bold numbers, command syntax, packet types, and decision rules. The goal is quick recall
rather than long explanations.
Straight to the exam hotspots – no filler, just the stuff that actually shows up
---
1. ROUTING PROTOCOLS – OSPF vs EIGRP Head‑to‑Head
The Big Comparison
Feature OSPF EIGRP
Type Link‑state Advanced distance‑vector
Algorithm Dijkstra SPF DUAL (Diffusing Update Algorithm)
Vendor Open standard (RFC 2328) Cisco‑proprietary (now RFC 7868
informational)
Default AD 110 90 (internal) / 170 (external)
Metric Cost (based on bandwidth) Composite (bandwidth + delay by
default)
Convergence 5‑40 sec (untuned) Very fast (if feasible successor exists)
Exam weight Heavy (~10‑12 questions) Moderate (~4‑6)
What they test Neighbor states, DR/BDR, LSA types, Basic config, K‑values, successor/FS
areas
---
Administrative Distance – Memorize This Order
Lower AD = more trusted. When two protocols know the same route, the lowest AD wins.
Route Source AD
Connected 0
Static 1
EIGRP (internal) 90
OSPF 110
IS‑IS 115
RIP 120
EIGRP (external) 170
---
CCNA 200-301 • Last-Minute Power Sheet Page 1
, OSPF Metric Calculation – The Formula You Must Know
Cost = Reference bandwidth ÷ Interface bandwidth (rounded up, min 1)
Default reference bandwidth = 100 Mbps
Interface Speed Default Cost Gotcha
10 Mbps 10 —
100 Mbps (FastEthernet) 1 —
1 Gbps 1 ️ Same as 100M!
10 Gbps 1 ️ Same as 100M!
Exam trap: With the default reference, OSPF can't tell 100M from 10G – they all cost 1. Fix it
with:
auto-cost reference-bandwidth 10000 (sets reference to 10 Gbps)
OSPF runs directly over IP – protocol number 89
---
EIGRP Metric – Quick Facts
• Default K‑values: K1=1, K3=1, others = 0 → Metric = bandwidth + delay
• Neighbor requirements: Same AS number AND matching K‑values
---
OSPF Neighbor States – The Sequence You'll See on the Exam
DOWN → INIT → 2WAY → EXSTART → EXCHANGE → LOADING → FULL
State What’s Happening
DOWN No Hello received
INIT Hello received, but didn't see own Router ID
2WAY Bi‑directional communication established (DR/BDR
election happens here)
EXSTART Ready to exchange Database Descriptors (DBD)
EXCHANGE Swapping DBD packets
LOADING Requesting missing LSAs (sending LSRs)
FULL Adjacency complete!
OSPF multicast addresses:
• 224.0.0.5 – all OSPF routers
• 224.0.0.6 – DR/BDR only
---
OSPF Packet Types – The 5 Brothers
Type Name Purpose
1 Hello Discover and maintain neighbors
2 DBD (Database Description) Summarize LSDB contents
3 LSR (Link‑State Request) Ask for specific LSAs
CCNA 200-301 • Last-Minute Power Sheet Page 2
