Cheat Sheet CCNA
Class A: 255.0.0.0
Class B: 255.255.0.0
Class C: 255.255.255.0
Bits
also denoted as /8
also denoted as /16
also denoted as /24
(CIDR)
(CIDR)
(CIDR)
Increment
1
27
128
1
26
64
1
25
32
1
24
16
1
23
8
1
22
4
1
21
2
1
20
1
Subnet mask
Usable Host
A/8
B/16
C/24
128
126
/9
/17
/25
192
62
/10
/18
/26
224
30
/11
/19
/27
240
14
/12
/20
/28
248
6
/13
/21
/29
252
2
/14
/22
/30
254
/15
/23
/31
255
/16
/24
/32
Routing
Protocols
Config.
Statements
Required
Watch for
RIP v1
RIPv2
Distance vector
Slow convergence
Distance vector
Slow
convergence
Hop count
Router rip
Ver 2
Network X.X.X.X
no autosummary
Hop count
Router rip
Network X.X.X.X
Network X.X.X.X
no auto-summary
OSPF
EIGRP
Link-state
Fast
Advance Distance vector
Faster
Bandwidth
Bandwidth, cost, reliability, delay
Router EIGRP 2
Net X.X.X.X
Net Y.Y.Y.Y
No auto-summary
Router ospf 1
Net X.X.X.X wildcard mask Area 0
Net Y.Y.Y.Y wildcard mask Area 0
Process ID
Wild card mask must be correct
Area must be added
Hello and dead timer
Process ID 1-65535
Wildcard mask
Calculation
 AS number must be the same
 no auto-summary
Autonomous system number (AS)
Successor (in the routing table)
Feasible successor( backup route in
the topology table)
255.255.255.255
- 255. 255. 255. 0 (actual Subnet mask)
0 .0. 0. 255
Router ID
Router ID has 3 criteria for assignment
1. Could be manually assigned
2. Use Loopback address
i.
If more than one
loopback exit, loopback
with highest IP address
will be used
3. The physical interface with the
highest IP address will be used.
Cheat Sheet CCNA
Spanning Tree Protocol
1. Switch Priority determines who the root bridge is
2. MAC address used if priorities are the same
3. BPDU still go through alternate ports
4. All ports on root bridge are Designated ports (forwarding packets)
5. Root ports connect other switches to root bridge (also Designated
ports)
6. Alternate ports are in “Block Mode”
Spanning-tree port fast will convert STP to RSTP (port will change from
“blocked” directly to “forwarding” mode
Access Control List (ACL)
Synthax
 Standard and Extended
 Standard(1-99)
 Extended (100-199)
Access-list 100 permit tcp host X.X.X.X host Y.Y.Y.Y eq 80
Access-list 100 deny tcp any host Y.Y.Y.Y eq 80
Access-list 100 permit ip any any
(access-list <number> <action> <protocol> <Source><Destination>
ES vs SD
To apply:
Navigate to the interface of choice and do
IP access-group 100 in
End
Copy run start. (very important step)
Troubleshooting
tips
Ping
Traceroute
Show ip protocols
Show ip interface brief
Show ip route