Ccna Exam Flashcards
1
Q
What info can you see in MAC address table? (4)
A
Vlan
MAC address
Type
Ports
2
Q
What fields are in a UDP Header (5)
A
64 bits long
Source Port 16 bits
Destination Port 16 bits
Length 16 bits
Checksum 16 bits
Data - Size varies
3
Q
Does Layer 2 switch have a MAC address?
A
Yes for remote access management
4
Q
What speeds does Cat6a cable support
A
10G
5
Q
What commands are used to configure DHCP?
A
Interface [interface] IP address dhcp
6
Q
What commands can be used to see the application ports available?
A
Show control-plane host open-ports
7
Q
Steps for switch install (6)
A
- Confirm power and environmental needs
- Rack and stack
- Verify cabling
- Connect power (switch has no power button so will automatically turn on now)
- Watch boot- POST begins and switch LEDs blink. Then IOS text output shown
- Ready to config
8
Q
What info is displayed in show control-plane host open-host
A
Protocol (tcp or UDP)
Local address (port number)
Foreign address
Service (ssh-server, telnet, HTTP core, NTP)
State - listen, establish
9
Q
What speeds does Cat5e support?
A
1G
10
Q
What types of memories are there on routers? (4)
A
RAM - volatile- lost when powered off - holds running config
NVRAM - stays when powered off - holds startup config, software configuration register
ROM - can’t change - used to recover pwd, download software, holds bootstrap
Flash - holds IOS
11
Q
How does ARP work if IPv4 address outside the network
A
Asks for the MAC for IP….sees not in subnet Sends out default gateway
12
Q
What are the capability codes in show cdp neighbor
A
R-Router
T-trans bridge
B-source route bridge
S-switch
H-host
I-IGMP
r-repeater
13
Q
What info is displayed on show cdp neighbors? (6)
A
Device ID
Local Interface (interface on this dev connected to neighbor)
Hold time (how long to hold data)
Capability code
Platform
Port ID (interface on neighboring dev that is connected to this one)
14
Q
What speeds does Cat5 cable support
A
100M
15
Q
What speeds does Cat7 cabling support
A
10G
16
Q
What commands can you use to exit interface config mode? (1)
A
Exit
17
Q
What commands do you use to set IP address to an interface?
A
Config t Interface [interface] IP address [ip] [subnet mask] No shutdown
18
Q
What commands do you use to change host name
A
Config t Hostname [hostname]
19
Q
What applications does TCP/IP support? Give application, port number and if TCP or UDP (8)
A
FTP. 21. TCP
SSH. 22. TCP
Telnet 23 TCP
HTTP 80 TCP
HTTPS 443 TCP
DNS 53 TCP and UDP
TFTP 69 UDP
SNMP 161 UDP
20
Q
What commands do you use to clear the MAC address table?
A
Clear MAC address-table dynamic
21
Q
What commands can be used to exit privileged exec mode? (2)
A
Disable
Exit
22
Q
What are the flags available in TCP header
A
They are control bits
Nonce Sum (NS) - enables receiver to show aegis ack
Congestion Window Reduced (CWR) - ack the congestion-id’ing echoing received
Explicit Congestion Notification Echo (ECE) - ids congestion
Urgent - data should be prioritized over other data
Acknowledgment (ACK) - used to ack
Push (PSH)- IDs app data to be transmitted immediately and not wait for entire TCP seg
Reset (RST) - IDs connection be reset
Synchronize (SYN) - synch sequence #s
Finish (FIN) - IDs no more data from sender
23
Q
What commands are used to configure DHCP relay?
A
Interface [interface] Ip helper-address [DHCP server IP]
24
Q
What info can you get from show version (5)
A
Lots but IOS software version Switch up time System image file Switch platform Processor board ID
25
How does MAC address table get updated? (6)
1. Switch gets frame from PC A on port 1
2. Switch enters source MAC of PC A and switch port received on in MAC table
3. Switch checks table for destination MAC. If address unknown it floods frame to all ports except one received on
4. Destination device with matching MAC replies with unicast frame to PC A
5. Switch enters source address of PC B and port number of switch port received frame on into MAC table
6. Now can forward frames between PC A and PC B
26
Provide media, max length and connector type for 1000BaseSX
62.5/50 micron MMF
275m or 550m
Optical fiber connector
27
What info is displayed for show cdp neighbors detail
ip addys configed on neighbor device
Version of software it’s running
Management ip
28
What are class A IP addresses? How many octets are network? What binary does it start with? Valid address range? Valid public IPs? Valid private IPs?
Huge networking up to 16M hosts
First octet network
Starts binary 0
Range 1-126
Public 1.0.0.0 - 9.255.255.255 and 11.0.0.0 - 126.255.255.255
Private 10.0.0.0/8
29
What IP is used for loopback
127.0.0.1
30
What command clears one ip from the arp table
Clear ip arp 192.168.3.2
31
What commands are used to leave user EXEC mode? (3)
Logout
Exit
Quit
32
What is UTP? What speeds does it support? What length cable does it support?
Unshielded Twisted-Pair Cable - 4pair-cheap
Speeds 10M to 50G
Supports up to 100m or 328 ft (30m if 40G)
33
IP address size and portions
32 bits
Made up of network and hosts
34
What commands are used to turn off CDP
Config t
No cdp run Interface [interface]
No cdp enable
35
What are Class D IP addresses? What binary do they begin with? What are the valid address ranges?
Multicasts Always destination addresses
Begins with binary 1110
224-239
36
What uses straight through cabling (3)? What uses crossover cabling? (4)
Straight through (unlike)
Switch to router
Switch to PC
Switch to Server
Cross over (like to like)
Switch to switch
Router to router
Router to PC
PC to PC
37
What types of ports are there on routers?
Management
Network
38
What commands do you use to add a description to an interface?
Config t Interface [interface]
Description [description]
39
What are Class B IPs? What portion is network? What binary do they start with? What is the address range? What are valid Public IPs? What are valid Private IPs?
Moderate to large businesses with more than 65,000 hosts
First two octets network
Binary starts with 10
Address range 128-191
Public IPs 128.0.0.0 - 172.15.255.255 and 172.32.0.0 - 191.255.255.255
Private IPs 172.16.0.0/12
40
What commands can you use to verify duplex modes? (1)
Show interfaces [interface]
41
What commands are used to set duplex and speed settings on interfaces?
Config t
Interface [interface]
Duplex [full] or [half] or [auto]
Speed [speed] or [auto]
42
How can you use ARP to resolve MAC of local IPv4 address?
PC sends ARP broadcast for MAC addy of specific IP within same network
Gets back ARP reply via a unicast from the PC that owns the IP with the MAC address
Updates ARP table
43
What are Class E IP addresses? What binary do they start with? What are the valid IP ranges?
Experimental
Never assigned to hosts
Begins with binary 1111
240-255
44
Provide media, max length, and connector type for 1000BaseLX
9-micron SMF
5-10k
Optical fiber connectors
45
What commands can you use to view MAC address on interface? (2)
Show interface [interface] | include address
Or
show interfaces [interface] | include bia
46
What speeds does Cat6 support
10G
47
What commands do you use to set a default gateway?
Config t ip default gateway [ip]
48
What fields are in IPv4 headers? (14)
Source Type - info on QoS
TTL - lifetime of packet (1-255)
Source IP
Destination IP
Version of IP
IHL - internet header length
Total Length ID - used to unfragment IP
Flag - regards to fragmentation
Fragment offset - IDs where frag belongs
Protocol - upper layer protocol (like 6 is TCP)
Header Checksum - used error detection Options - optional parameters
Padding - extra data to ensure ends on 32 bit boundary
49
What commands can be used to confirm Interface configs and status
Show ip interface brief
Show protocols [interface]
Show interfaces
50
What commands can be used to see what interfaces you are connected to?
Show cdp neighbors
Show lldp neighbors
51
What commands can be used to exit global config mode? (3)
Exit
End
ctrl-Z
52
Provide media, max length, and connector type for 100BaseFX
62.5/125 micron MMF
400 meters
Duplex MIC ST
53
What are the functions of TCP/IP (6)
Session Multiplexing
Identifying applications
Segmentation
Flow Control
Connection-Oriented Protocols
Reliability
54
What info can you get from show interface [interface] (4)
Is physical and line protocol up?
MAC info - type and MAC address
Duplex/Speed 5 min
Input rate (interface traffic stats)
55
What are headers in Ethernet frame? (6)
Preamble (8 bytes) - used to synchronize the signals
Destination MAC (6 bytes)
Source MAC (6 bytes)
Type (2 bytes) - code that IDs network layer protocol
Payload (46-1500 bytes) - network layer data (if not 46 bytes will add padding)
FCS (4 bytes) - checks for errors via CRC
56
The difference between a ARP cache and MAC address table
ARP cache is on host
ARP is MAC to IP address table
MAC address table is on a switch
MAC address table is MAC address and physical port info and VLAN
57
Provide media type, max length and connector type for 1000BaseT
Cat5e UTP (4 pair)
100m
RJ-45
58
Where is the MAC address table stores?
In CAM memory
59
What is a MAC address
IDs NIC interface of device -hard coded or burned in Link layer address
12 hexadecimal numbers
48 bits
1st 24 are OUI (manufacturer of NIC)
Last 24 are vendor assigned end station
60
What commands are used to turn off an application port on a router?
Config t
No ip [port name]
i.e.: no ip http server
61
What info does show running-config provide
A lot of info
See IP address
See default gateway
62
What is the max length for Ethernet gram
1518 bytes
63
What commands can be used to confirm IPv4 config is correct? (3)
Show running config interface [interface]
Show ip interface brief Ping
64
What are the routers components? (4)
CPU
Motherboard
Memory
Ports
65
Provide media, max length and connector type for 100BaseTX
Cat5 UTP (2-pair)
100 meters
RJ-45
66
What IP address is used to AutoConfig IPv4
169.254.0.0/16
67
What are the Switch LED lights and what do they mean? (8)
SYS- system status
RPS - status of Redundant power supply
STAT - each port LED status of that port
DUPLX - duplex of port...on is full duplex off is 1/2 duplex
SPEED - off is 10M, solid green is 100M, flashing is 1G
PoE - if on supplying PoE
Mode - toggles thru STAT, DUPLX, SPEED, PoE
Port - based on port mode
68
What are Class C IP addresses? How many octets are network? What binary does it start with? What are valid address ranges? What are the Public Ranges? What are the Private Ranges?
Most common - for small medium Max 254 hosts
First three octets network
Begins binary 110
192-223
Public range 192.0.0.0 - 192.167.255.255 and 192.169.0.0 - 223.255.255.255
Private range 192.168.0.0/16
69
What fields are in TCP header?
Minimum 20 bytes
Source 16 bits
Destination 16 bits
Sequence number 32 bits
Header length 4 bits
Reserved 3 bits
Flags 9 bits
Window size 16 bits - flow control
Checksum 16 bits
Urgent pointers 16 bits - if urg flag set - offset from seq number id’ing last urgent data byte
Options 0-320 bits - determined from data offset field
Data size varies - upper layer data
70
What commands can be used to confirm default gateway is set (3)
Show running-config | include default
Show ip route
Ping
71
What commands are used to enable/disable LLDP?
Config t
[no] lldp run
[no] lldp transmit
[no] lldp receive
72
What services does ARP provide?
Address resolution to map IPv4 addy to
MAC addy Caches MAC addy learned by ARP
73
What IP is used for Broadcasts
255.255.255.255
74
What commands do you use to view MAC address table?
Show MAC address-table
75
What commands are used to configure router to be used as DHCP server?
ip dhcp excluded-address [IPs to exclude with space between them]
ip dhcp pool [pool name]
network [network / subnet]
default-router [ip]
dns-server [ip]
domain-name [domain name]
lease [days] [hours] [minutes] [infinate]
76
How can you see the arp cache
Windows machine: arp -a
Router: show ip arp
77
What IP is used for Directed Broadcasts?
Network ID + highest broadcast
ie for 10.0.0.0/8 is 10.255.255.255
78
What speeds does Cat8 cabling support?
40G
79
What info does show ip route display?
All learned IP addresses and how learned.
This includes subinterfaces provisioned on router on a stick configuration
80
What info can be viewed on show ip arp
Protocol
Address
Age
Hardware Address
Type
Interface
81
Basic Troubleshooting tools
show logging
ICMP (Ping/Traceroute)
show controls
Telnet/SSH
arp
82
Ways to verify end to end ip connectivity
ping (can ping from certain interface using command: ping [ip] source [interface])
traceroute (can ping from certain interface using same as ping)
\*ping/traceroute from loopback too
Telnet/SSH (see if you can get to equipment via IP)
show ip arp (verify connected devices)
show ip interfaces brief (see IP config on all interfaces)
83
Troubleshooting common media issues
Use sho inter and confirm
1. if physically down - if down check cable/connectors for damage
2. check noise - increased error counter in output. Confirm cable length
3. confirm collisions - verify duplex settings on both sides
84
Common media problems - Copper
Damage to wiring
New electronics installed causing EMI
Traffic patterns change
New equipment installed
85
Common media issues - fiber
Microbends/macrobends
Splice losses
Dirty connectors
86
Troubleshooting Switch Port issues
verify duplex and speed settings on both sides.
87
Troubleshooting physical connectivity issues
show interfaces
Confirm interface up
Input queue drops (more traffic than can handle) - look at CPU
Output queue drops (packets dropped bc congestion) - look at QoS
Input errors - problems in reception of frame (CRCs) - look at cabling, interface hardware, duplex
Output errors - issues sending frame (like collision) - look at duplex settings
88
Step to troubleshoot ipv4 addressing
1. Verify IPv4 address and subnet mask
2. Ping the loopback address
3. Ping IPv4 address of local interface
4. Ping the default gateway
5. Ping remote server
89
How do you configure static route?
ip route [ipv4 destination network ip] [ipv4 destination network subnet mask] { [IPv4 address of next-hop router] OR [outbound interface of local router (s0/0/0)] }
90
What is a "host route"?
Static route for single host and uses subnet mask of 255.255.255.255
91
What is a floating static route?
Static route with AD greater than 1
Need to change the AD manually when configuring
ip route [ipv4 destination network ip] [ipv4 destination network subnet mask] { [IPv4 address of next-hop router] OR [outbound interface of local router (s0/0/0)] } [AD]
92
When is default static route used? How do you configure it?
\* Used when no other routes in routing table match dest IP of packet
\* When router has only one other router connected to it
Often connects edge router to ISP
ip route 0.0.0.0 0.0.0.0 [ip for interface to leave from]
93
What is the difference between a default static router and default gateway?
Default-routes set on routers
Default gateways set on hosts
94
How do you remove a static IP route
no ip route [network ip] [subnet mask] [nexthop ip] [ad if not 0]
95
How do you enable ipv6 routing on Cisco routers?
config t
ipv6 unicast-routing
96
How do you set static route in IPv6?
config t
ipv6 unicast-routing
ipv6 route [ipv6 network] [ipv6 mask] [outgoing interface] [ipv6 next hop]
(MUST PROVIDE outgoing interface if next hop is link-local address)
97
How do you see IPv6 static routes and what do you see?
show ipv6 route static
See routes set
98
What issues does VLAN address
Segmentation
Security
Network Flexibility
VLANs can be in different LANs but then still be in same broadcast domain
99
What commands do you use to set up VLAN
config t
vlan [number id]
vlan [vlan name]
100
What VLAN IDs can you use
0 is reserved
1 is default
2-1001 - Used for ethernet VLANs
1002-1005 - used for Token Ring, FDDI
1006-4094 - Used for ethernet VLANs
4095 - reserved
101
What do you need to do if you have 1 VLAN that crosses multiple switches
Create trunk to connect switches
102
How create VLAN with switchport
Under global config:
config t
vlan [vlan id]
name [vlan name]
interface [interface to config on]
switchport mode access
switchport [vlan name] vlan [vlan id]
103
How to verify VLANs and what data does it provide?
show interfaces [interface name] switchport
Shows how it was configed (static or dynamic)
Access Mode VLAN
Voice VLAN
104
What are the valid VLAN ranges
0 - Reserved
1 - Normal (Default)
2-1001 - Normal Ethernet VLANs
1002-1005 - For Token Rings and FDDI
1006-4094 - Extended Ethernet VLANs
4095 - Reserved
105
How do you provision a VLAN?
config t
vlan [vlan number]
name [vlan name]
106
What are the commands that define VLAN port membership modes and characteristics?
switchport mode access
switchport mode trunk
switchport voice vlan [vlan id]
107
What does switchport access mode do?
For VLANs
Static Access
Can only belong to one VLAN and is manually assigned to that VLAN
108
What does switch port mode trunk do?
Configs trunk
Member of all VLANs
Allows switches to exchange VLAN traffic between them via tagging
802.1q
109
What does switchport voice vlan [vlan-id] do?
Is a voice VLAN
Attached to Cisco Phone
Uses one VLAN for voice and another for data
110
What commands used to assign port to a Data VLAN?
config t
interface [interface]
switchport mode access
switch port access vlan [vlan number]
111
How can you configure multiple interfaces at once
config t
interface range FE0/1-3
112
What is a voice VLAN? How do you config that?
Voice VLAN is used if you have a VOIP phone that does tagging that also has data VLAN that does not do tagging
CREATE VLANs (voice and data)
config t
vlan [data vlan number]
name [data vlan name]
vlan [phone vlan number]
name [phone vlan name]
ASSIGN VLAN TO PORT
interface [interface]
switchport mode access
switchport voice vlan [phone vlan number]
switchport access [data vlan number]
113
Ways to verify VLANs
show vlan
show vlan [vlan number]
show vlan brief
show interfaces [interface] switchport
114
What info is displayed on show vlan?
VLAN
Name
Status
Ports
115
What info does show vlan id [vlan number] show?
VLAN
Name
Status
Ports
116
What info does show vlan brief show?
VLAN
Name
Status
Ports
117
What is DTP?
Dynamic Trunking Protocol
Negotiates if interfaces btw switch should be in access or trunk mode
Dynamic Auto - Interface will form trunk if DTP msg received to do so from other side switch. Doesnt generate DTP msgs - only listens
Dynamic Desiarable - negotiate mode automatically - will try to convert line to trunk. Generates and listens for DTP. If port on other side of switch can form trunk it will.
118
What does sho int [interface] switchport show
Adminstrative mode (dynamic static or dynamic desirable)
Type of encapsulation
Operational mode
Native VLAN
Access Mode VLAN
Voice VLANs
see if VLANs are active
119
What is 802.1q?
Protocol for trunking for VLANs
Combines many VLANs on same port (switch to switch ports)
Allows tranport of frames from different VLANs
Each frame has tag for the VLAN (added by the trunk switch port)
Receive dev fwds frame to corresponding VLAN based on tag
Is switch to switch link
120
What info is added in the 802.1q tag
Type - value of 0x8100 to id as 802.1q tagged frame
Priority
CFI - 1-bit identifier enables Token Ring frames to be carried on ethernet links
VLAN ID
121
How do you configure an 802.1q trunk?
config t
interface [interface]
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk native vlan [vlan number]
switchport trunk allowed vlan [allowed vlans] (optional but must be same on both switches)
(must config identically on both switches)
122
How do you add a new vlan in allowed vlans on switchport?
Can either do:
switchport trunk allowed add vlan [new vlan]
OR
switchport trunk allowed vlan [list all vlans including new]
if you just do switport allowed vlan [new vlan] - will remove all other vlans.
123
124
What is the native VLAN?
It is the untagged VLAN
By default is 1 - but can change
Change with command: switchport trunk native vlan [vlan number]
VLAN 1 is also management VLAN and that cannot be changed (CDP, STP, LLDP always carried on VLAN 1)
If change native VLAN must be changed on both sides
125
How can you confirm the 802.1q configuration?
show interfaces [interface] switchport
show interfaces trunk
show interfaces status
126
What can you see in sho interfaces trunk?
Port
Mode (on - we turned on and not dynamic, dynamic desirable, auto)
Encapsulation
Status
Native VLAN
Vlans allowed
127
What can you see in sho interface status
Port
Name
Status (is connected?)
VLAN
Duplex (manual or auto?)
Speed (manual or auto?)
Type
128
Options to enable interVLAN routing
1. Router with separate Interface in each VLAN (takes up lots of space)
2. Router on a Sitck (prevalent)
3. Layer3 Switch with sub-interfaces
129
What is Router on a Stick?
Build a single trunk link between switch and router to be able to route multiple VLANs over one physical router port
Build separate subinterfaces on the port, enable the VLAN tagging, associate the default gateway for that subinterface.
130
How do you configure router on a stick on a router?
config t
interface [interface.subinterface] - usually subinterface=VLAN ID
encapsulation dot1q [vlan id]
ip address [default gateway for the VLAN host]
131
What ways can you verify the VLANs on router (for router on a stick)?
sho vlans
sho ip route
132
What info does show vlans show on a router?
VLAN ID
VLAN trunk interface
Protocols, IP Address, Transmitted/Received
Encapsulation
133
What functions do dynamic routing protocols fulfill
Discover remote networks
Maintain up to date routing info
Choose best path to destination network
Find new best path if current is not available
134
Difference between IGP and EGP?
Interior Gateway protocols - withing my own AS
OSPF, EIGRP
Exterior Gatway protocol - outside my AS
BGP
135
Difference between distance vector and link state?
Are dynamic routing protocols
Distance Vector = EIGRP and RIP - relies on info neighbor is providing. Only looks at hops
Link State = OSPF and ISIS - looks at state of every link and who is connected to who
136
Explain difference between path selection and adminstrative distance
Adminstrative distance is the "trustworthiness" of the route (different protocols use different ADs)
Path Selection is to select the preferred route if multiple routes available (looks at speed or hops)
137
Classless vs classful in dynamic routing protocol
Classless - RIP v2, EIGRP, OSPF, IS-IS, BGP
Advertises subnet masks (can support discontiguous networks)
Classful - RIPv1 and IGRP
138
ADs for common protocols
0 - Connected
1 - Static
20 - EBGP
90 - EIGRP
110 - OSPF
115 - IS-IS
120 - RIP
170 - External EIGRP
200 - Interal BGP
255 - Unreachable
139
What are the key features of link-state protocols?
1. Scalability
2. All routers have full map of topology
3. Updates sent out when topology changes and periodically
4. Respond to topology changes quickly
5. More info exchanged btw routers
140
Three tables used in link-state protocols?
1. Neighbor Table
2. LSDB - Link State Database
3. Routing Table
141
How do Link State Database works
1. Neighbor relationships established
2. Sync LSDB by exchanging Link State Advertisement
3. Store the LSAs in LSDB
4. Applies SPF algorithm (via Dijkstra algorithm) to LSDB to calculate the shortest path.
5. Shortest path applied to the routing table.
142
What are LSAs?
Link State Advertisments
Describes router and networks connected to router
143
What is OSPF?
Open Shortest Path First
Link state routing protocol
IGP
Layer 4 protocol
144
What are the two-layer network hierarchy primary elements in OSPF?
AS - Autonomous System - all networks under a common adminstration
Area - grouping of contigous networks
145
Explain a multiarea design in OSPF
You have a backbone area (area 0)
All non-backbone areas must be connected to the backbone
Routers in nonbackbone area are internal routers - all have interfaces only in 1 area
Area border routers (ABR) connects area 0 to non-backbone areas
146
Explain ABRs in connection with OSPF
ABR = area border routers
routers that connect different areas with the backbone.
Contain LSDB for each area
Make route calculations for each area
Advertise routing info btw areas
147
Explain an ASBR in conjunction with OSPF
AS boundary router
At least one interface connected to OSPF area and one interface connected to non-OSPF (like our peering routers) maybe EIGRP or BGP
148
Explain how OSPF works
Creates neighbor by exchanging hello packets
Propagates LSAs:
Links (Router Interfaces)
State (Desc of interface and relationship to neighbor routes)
Floods LSAs to all OSPF routers in area
Peices together all LSAs to create the LSDB
Uses SPF algorithm
149
When are LSAs sent out in OSPF?
When topology changes
Every 30 mins
150
What info is sent in hello packet and what must agree to establish neighbor relationship?
\* must agree
Router ID - 32bit number that IDs router - default is highest loopback addy. If not loopback then is highest IP on any interface. Can program yourself using "router-id" command
\*Hello/Dead Intervals - how often sends hello keepalive (default p2p is 10s). And how long btw hellos shoudl consider router down (default 4x the hello)
Neighbors
\*Area ID - also must have same subnet and subnet mask
Router Priority - 8 bit number - Uses to select DR and BDR
DR IPv4 addy
BDR IPv4 addy
\*Authentication data
\*Stub area flag - special area
151
What happens when install new router on OSPF network
1. Router interface enabled - OSPF is down b/c no info exchanged yet. Sends hello packets
2. All directly connected routers that are running OSPF add router to list of neighbors. They are then in initial state (INIT)
3. Router that got hello sends unicast to the router with info listing all neighbor routers
4. When new router gets hello back with its own router showing as neighbor - adds neighbors own table now in two way
152
Explain DR and BDR ins OSPF
Designated Router and Backup Designated Router
Router with highest priority is the DR
Used in multiaccess broadcast networks (like a LAN)
One DR per LAN
Routers only communicate with DR by using OSPF DR multicast 224.0.0.6
DR communicates with all via 224.0.0.5
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Provide the exchange protocol with the DR and BDR in OSPF
Starts in exstart state
1. Prim/Second relationship created btw router and DR/BDR. Router with highest RouterID will be primary during exchange
2. Prim/Sec routers exchange one + DBD (database description) packets with summary of LSDB (exchange state)
3. Router compares DBD with LSAs of own. If DBD has more recent LS entry - sends LSR (Link State Request) to ther other router. (When send LSR in loading state)
4. Router sends LSU (link state update) with entries req in the LSR. When all LSR provided - they are synced and in full state
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How do you update the reference bandwidth in OSPF
ospf auto-cost reference-bandwidth [bandwidth in kilobits/sec]
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How can you update the cost on an interface for OSPF?
ip ospf cost [cost]
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How do you overwrite the interface bandwidth in OSPF?
bandwidth [kilobits per sec]
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How to do you determine the cost of a route in OSPF
Cumulative add all the egress interface costs and lowest wins
If two paths are equal we will load balance between the two
(if you do above in show ip router you'll see two paths to the destination IP)
You can see both the routes also in the LSDB
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What types of protocol packets for OSPF are there to build LSDB?
1. Hello -discovers and maintains neighbors
2. DBD - database description packet with summary of LSDB
3. LSR - sent when want more info on a LSA it doesnt have
4. LSU - sent in response to LSR with LSAs to be updated
5. LSAck - ensures reliable transmission (DBD, LSR and LSU responses
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What commands can you use to see OSPF configs?
sho run | section OSPF
sho ip protocols
sho ip ospf
sho ip ospf int brief
sho ip ospf neighbor
sho ip route (see whats learned via OSPF)
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What info does show run | section ospf show?
see router id
see networks running and the area
what type of path (p2p etc)
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What does show ip ospf tell you?
router id
how long process has been running
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What info do you see in sho ip ospf int bri?
see what interfaces are running ospf
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What info do you see in sho ip ospf neigh?
Neighbor Ips
State (full bdr dr etc)
dead time
address
interface
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How do you configure OSPF?
config t
router ospf [process id]
router-id [router id}
(next step can be done on indiv interfaces or network command below is showing network command - this will apply to any interface on the router in the network ip)
network [network ip] [wildcard mask] area [area number]
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What happens in OSPF if you config "passive-interface" or
Means you will not send out OSPF packets out that interface.
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Spanning Tree what its used for and the steps
Eliminates potential L2 loops if redundancy built into network by disabling interfaces that may cause loops
1. Elects root bridge - based on priority and MAC (if priority is same then use lowest MAC)
2. Elects root port for each non-root switch
3. Elects designated port for each segment
4. Port transitions to forward or blocking state
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What is the purpose of NAT?
Network Address Translation
NAT takes private IPs unroutable outside the LAN and translates to public IPs
Usually on edge routers to convert from private to public right before leaving the LAN
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What is the difference between NAT and PAT
NAT and PAT serve same purpose - but PAT allows to overload with numerous private IPs mapped to the same public IP.
Keeps track by assigning a unique port number to each private IP.
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What are the 3 different types of NAT
Static NAT
Dynamic NAT
Port Address Translation (PAT)
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How configure Static NAT
config t
ip nat inside (saying that this is on the inside interface) source (saying NATing based on source IP) static (type of NATTING doing) [inside local address] [inside global address]
Also must set interfaces for inside and outside
config t
int [int inside]
ip nat inside
int [int outside]
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How to config dynamic NAT
Four Steps:
1. Create the ACL rule for what will get NATTED
config t
access-list 1 permit [ips to NAT]
2. Create the inside and outside interfaces
config t
int [inside interface on router]
ip nat inside
int [outside interface on router]
ip nat outside
3. Create the public IP pool
config t
ip nat pool [NAT-POOL-NAME] [first ip in public range] [last ip in public range] netmask [network mask]
4. Set up the NAT rule:
config t
ip nat inside (private ips) source (looking at sources) list [ACL num] (where to look to determine if NATTED) pool [NAT-POOL] (what public IPs to assign)
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NAT Terms
Inside Local Address - IP addy of inside network used in all packets inside the network (private)
Inside Global Address - IP addy of the internal dev as it appears to other networks (public) - the translated IP
Outside Local Address - IP of external dev as appears to internal network
Outside Global Address - IP addy of external dev as seen externally (usu same as outside local)
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How to configure PAT
3 parts:
1. Create ACL rule for what gets NATTED
config t
access-list 1 permit [IPs to NAT] [Wildcard Mask]
2. Create the inside and outside interfaces
config t
int [int on inside]
ip nat inside
in [int on ouside]
ip nat outside
3. Set the NAT rule
ip nat inside souce list 1 interface [outside interface] overload
