CCNA3 Review 100 Q/As for Modules 3 thru 8 Rev. 2a
Module 3: Enhanced Interior Gateway Routing Protocol
1. EIGRP - Default administrative distance = 90
Connected interface 0
Static route 1
(Internal) EIGRP 90
IGRP 100
OSPF 110
RIP 120
2. EIGRP Neighbor Table contains
o Neighbor layer address
o Hold time (Hold Uptime)
o Smooth Round-Trip Timer (SRTT)
o Queue count (Q Cnt)
= Number of EIGRP packets waiting to be sent
o Sequence Number (Seq No)
3. EIGRP DUAL - Primary Route
o Stored in Routing table and Topology table
4. Why Bandwidth needs to be configured on a port
(default bandwidth = T1 = 1.544 Mbps)
o a suboptimal route may be chosen
o the network may not be able to converge
5. EIGRP Topology Database (or Topology Table)
for a destination route
o contains all of the EIGRP routing tables
in the Autonomous System
o the routing protocol
o the Feasible Distance (FD) of the route
o the Reported Distance (RD) of the route
o can use: RT1#show ip eigrp topology
RT1#show ip eigrp topology
RT1#show ip eigrp topology
RT1#show ip eigrp topology all-links
6. Display EIGRP routing table
RT1#show ip route
RT1#show ip route eigrp
7. Command to monitor EIGRP activity
RT1#debug eigrp fsm
RT1#debug eigrp packet
8. EIGRP tables
o topology, neighbor, routing
9. Bounded updates by EIGRP
o partial updates
o sent only to certain routers that need this info
10. EIGRP layer 4 protocol
o RTP = Reliable Transport Protocol
11. Why does OSPF (EIGRP?) form adjacencies
o New routers can discover neighbors quickly
o Discover when a neighbor goes down
12. Discover OSPF neighbor
RT1#show ip ospf neighbor
RT1#show ip ospf neighbor detail
Display EIGRP neighbor table:
RT1#show ip eigrp neighbors
RT1#show ip eigrp neighbors details
13. "EX" in EIGRP routing table
o routes learned from other routing protocols
o EIGRP routes learned from other ASs
14. EIGRP - when you need to send across a serial link
from 192.168.1.65/26 to 192.168.1.129/26
(subnets 192.168.1.64/26 and 192.168.1.128/26)
o EIGRP will summarize the route on a classful
boundary - as 192.168.1.0
o must add "no auto-summary"
RT1(config)#router eigrp 101
RT1(config-router)#no auto-summary
RT2(config)#router eigrp 101
RT2(config-router)#no auto-summary
15. EIGRP Successor "primary route" goes down and no
Feasible Successor in topology table
o DUAL sets failed route = "active"
16. EIGRP - view all routes
RT1#show ip eigrp topology all-links
17. EIGRP AS 101 has a common border router to
IGRP AS 101.
o The IGRP route will be tagged with "EX"
in the EIGRP routing table
18. Metrics
o EIGRP uses a 32-bit metric
o IGRP uses a 24-bit metric
Therefore, we multiply the IGRP metric by 256
to obtain an equivalent EIGRP metric.
(Multiplying by 256 is equivalent to shifting
a binary value by 8 bits to the left.)
Module 4: Switching Concepts
1. Adaptive cut-through
Some switches perform cut-through switching on a
per-port basis until a user-defined error threshold
is reached. Then the ports automatically change over
to store-and-forward mode. When the error rate falls
back below the threshold, the port automatically
changes back to cut-through mode.
2. Building a switching table
o Incoming frames: Store source MAC addresses
3. Switch latency
o internal time delay within the switch
4. Asymmetric switching
o needed when some ports operate at different speeds
o client/server environment, where server is faster
o need more buffer memory
5. Hubs
o Layer 1
o output to all ports except input port
o all hosts on the segment share the bandwidth
6. Bridge
o uses MAC table to make forwarding/filtering decisions
7. Bridge buffering
o needed for store-and-forward switching
8. CISCO LAN switch
o uses CAM memory
9. Shared memory buffering
o single (input) queue
o all (incoming) frames share a common memory buffer
10. Layer 2 broadcast
o 48 bits = all ones binary = FF FF FF FF FF FF hex.
11. Cut-through Fast-forward
o begins forwarding as soon at the destination address
is received
12. Router functions
o segments broadcast domains and collision domains
o forwards packets via L3 (layer 3) address
13. L2 (layer 2) segmenting = microsegmentation
o enhance user bandwidth
o isolate traffic between segments
14. A switch is faster than a bridge because
o bridge uses (slower) software switching
o switch uses (faster) ASIC hardware switching
15. L2 switch
o increases bandwidth per user
o decreases size of collision domains
o isolates traffic between segments
Module 5: Switches
1. LAN design goals
o adaptablity, manageability, scalability
2. LAN design
o segment collision domains = layer 2
3. Network availability
o throughput, access to resources
4. TIA/EIA
o IM to HC = VCC
5. Hierarchical network design model: Access layer
o layer 2 filtering
o microsegmentation
6. Distribution layer switch (with RSM module)
o OSI model: layer 2 and layer 3
o "policy" switching
o can use ACLs
o packet filtering
7. Backbone
o layer 4
o core layer
8. Access layer
o allow end users access to the network
9. Workgroup
o distribution layer
10. Core layer
o redundant paths, high speed, no packet filtering
11. Distribution layer
o policy and security
o where packet manipulation takes place
o isolates network problems to the workgroups
in which they occur
o do not burden the core layer with policy and security
12. If design goal not met
o functionality
13. Able to grow from 10 to 100 to 1000 speed
o scalability, adaptability
14. Increase number of broadcast domains
o VLANs for each group
o routers
15. Enterprise servers
o email and DNS
o place these at the MDF
16. Workgroup servers
o support specific groups
o place these in IDF closest to users
17. IEEE 802.3
o CSMA/CD Ethernet
18. To send from VLAN1 to VLAN2
o need a router
19. More connections at end of cable runs
o hubs and switches
20. Why is vertical BW greater than horizontal BW?
o Vertical handles multiple area traffic
Module 6: Switch configuration
1. Connect new switch
o negotiates speed, such as 10 or 100
o default membership in VLAN1
o all switches can send ARPs
o deactivate port security
2. Switch - prevent unauthorized access
o assign ports statically
o shut down unused ports
o port security by MAC address
o password protect Priv Exec mode
3. Start-up config
o to initialize VLAN info, delete file vlan.dat
o delete flash:vlan.dat
4. Ways to exit
o CtrlZ, exit, end
5. Update the IOS
o use TFTP
6. Backup IOS
o copy flash tftp
7. Password recovery mode on 2900 switch
o hold down Mode button
8. Initial configuration of a new switch
o manually enter commands
o enter system dialog
9. Display command options for a command
o COMMAND ?
10. Host MAC address
o max-age = 300 second
11. copy tftp flash
o successful copy: exclamation point is displayed (!)
Module 7: Spanning Tree Protocol (STP)
1. Create a loop-free topology
o spanning tree
2. Converge
o one root bridge
o one root port per non-root bridge
3. BPDUs sent
o every 2 seconds
4. STP port states
o disabled
o blocking, listening, learning, forwarding
5. Recording MAC addresses but not forwarding
o learning
6. Forwarding state
o learning and forwarding
7. Redundant networks - potential problems
o broadcast storms
o multiple copies of a message continue to loop
o redundant copies of a message continue to loop
8. If you send a message through a redundant network
without STP protocol
o will cause a broadcast storm
9. STP - first step
o elect a root bridge
10. STP - select a root bridge - based on "Bridge ID"
o Bridge ID consists of 2-byte Bridge Priority plus
6-byte base MAC address of the switch
o bridge priority
16 bits: range is 0 to 65k, default = 32768
force a winner: change to a value less than 32768
o switch with lowest Bridge ID becomes the root bridge
11. BPDU information
o contain the "shortest path" and "which ports will forward"
o Root BID: who is the root bridge
o Root Path Cost: how far away is the root bridge
o Sender BID: who sent this BPDU
o Port ID: what port on sending switch sent this BID
12. ARP broadcast
o has the IP address, needs to learn the corresp. MAC address
o layer 2 broadcast = FF FF FF FF FF FF hex. = 48 bits of ones
13. STP topology change
o traffic will be disrupted
o delay up to 50 seconds (20 plus 15 plus 15)
o delay controlled by timers (default: 20 + 15 + 15 seconds)
14. STP versions
o STP = IEEE 802.1d = default converge in 50 seconds
o RSTP = IEEE 802.1w = default converge in 15 seconds
15. STP convergence time depends on
o max-age timer (default: 20 seconds)
o listen timer (default: 15 seconds)
o learn timer (default: 15 seconds)
16. STP (802.1d) vs RSTP (802.1w)
STP RSTP
blocking discarding
listening discarding
learning learning
forwarding forwarding
disabled discarding
17. RSTP link types
o point-to-point link: forward immediately
o edge port: forward immediately
o shared port: go thru discarding/learning/forwarding
18. Multicast
o switch treats same as a broadcast
o floods out all ports, except the source input port
19. Five nines
o 99.999% availability
Module 8: Virtual LANs (VLANs)
1. Delete an existing VLAN
o all ports assigned to that VLAN become inactive
2. Communicate between VLAN1 and VLAN2
o need a router
3. VLAN Dynamic switch port configuration
o can use MAC addresses or IP addresses
4. VLAN Static switch port configuration
o seldom moved
o robust management software
o overhead for dynamic is not desirable
5. Configure VLAN3
o SW1(config)#interface fa 0/10
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 3
6. Delete an entire VLAN
o delete VLAN database: delete flash:vlan.dat
7. Fastest VLAN configuration
o membership by port = static VLAN
8. Example of network with 3 VLANs
o 3 broadcast domains
9. Switch behavior
(didn't copy this...)
10. Display VLAN information
o show vlan
o show vlan id
o show vlan name
11. VLAN benefits
o flexibility
o add/move
12. Initial new switch configuration
o CDP to VLAN1
o all ports are default members of VLAN1
13. ?
o router IOS
o speed
14. Root bridge
o central bridge with STP topology
15. Number of VLANs you can assign per switch
depends on
o traffic patterns
o applications
o workgroup functions and commonality
16. VLAN frame identification
o ISL (Cisco proprietary, now becoming obsolete)
= encapsulates each frame
o IEEE 802.1q (dot1q) Frame Tagging
= adds a tag field within each frame
17. Switch receives a message with unknown source address
o switch adds source MAC address to CAM table
Note: If you find errors/omissions, or have suggestions to improve this
documentation please send an email to patmoss@patmoss.com. Thanks.
Return to Top
|