interconnecting cisco networking devices part 2 (icnd2 ... · pvst+ : a cisco enhancement of stp...
TRANSCRIPT
Interconnecting Cisco Networking
Devices Part 2 (ICND2)
Course 01 - Implementing
Scalable Medium-Sized Networks
-
Slide 1
Lesson 1
Troubleshooting VLAN Connectivity
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Slide 2
VLAN Review
A VLAN represents:
A separate broadcast domain
A subnet (logical network)
An independent LAN
VLANs help with the following:
Segmentation of traffic
Security Boundaries
Flexibility in designing a network
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Slide 3
How to Create a VLAN
Adds VLAN 2 and names it “switchlab99”
Assigns interface FastEthernet 0/2 to VLAN 2
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Slide 4
How to Create a VLAN (Cont.)
Displaying VLAN information
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Slide 5
What is a Trunk
A Trunk can carry traffic for multiple VLANs
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Slide 6
How to Configure a Trunk
Create a trunk from interface configuration mode
Configure the Fa0/11 interface as a VLAN trunk
The native VLAN is changed to VLAN 99
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Slide 7
How to Configure a Trunk (Cont.)
Verifies switchport settings on FastEthernet0/11
Verifies that FastEthernet0/11 is trunking
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Slide 8
DTP
Avoid using DTP (manual configuration recommended
Configure both sides as trunks
The command nonegotiate turns off the negotiation
Dynamic
Auto
Dynamic
Desirable
Trunk Access
Dynamic
Auto
Access Trunk Trunk Access
Dynamic
Desirable
Trunk Trunk Trunk Access
Trunk Trunk Trunk Trunk Limited
Connectivity
Access Access Access Limited
Connectivity
Access
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Slide 9
VLAN Troubleshooting
Show vlan
Show mac address-table
Show vlan
Show interfaces
Show interfaces switchport
Yes Yes
No No
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Slide 10
VLAN Troubleshooting (Cont.)
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Slide 11
VLAN Troubleshooting (Cont.)
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Slide 12
Troubleshooting Trunks
Show interfaces trunk
Show interfaces trunk
Yes Yes
No No
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Slide 13
Troubleshooting Trunks (Cont.)
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Slide 14
Lesson 2
Building Redundant Switched Topologies
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Slide 15
Problems with Redundant Topologies
Redundancy avoids a single point of failure.
A redundant switch topology causes broadcast storms, multiple
frame copies, and MAC address table instability problems.
A loop-avoidance mechanism is required.
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Slide 16
Problems with Redundant Topologies (Cont.)
Solution: STP (Spanning Tree Protocol)
Provides a loop-free, yet redundant topology by dynamically
closing ports.
Published in IEEE 802.1D specification
X
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Slide 17
How Spanning-Tree Works
The spanning-tree algorithm follows these steps:
1. Elects a root bridge
2. Elects a root port for each non-root switch
3. Elects a designation port for each segment
4. Ports transition to forwarding or blocking state
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Slide 18
How Spanning-Tree Works (Cont.)
Switch A
Priority 28672
MAC 0000.0cab.3274
Switch D
Priority 32768
MAC 0000.0c39.f28a
Switch B
Priority 28672
MAC 0000.0c9f.3127
Root Bridge
Switch C
Priority 32768
MAC 0000.0cf6.9370
10Gbs
1Gbs1Gbs
1Gbs1Gbs
Step 1: Elect a Root Bridge
Decision based on lowest BID
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Slide 19
Switch A
Priority 28672
MAC 0000.0cab.3274
Switch D
Priority 32768
MAC 0000.0c39.f28a
Switch C
Priority 32768
MAC 0000.0cf6.9370
How Spanning-Tree Works (Cont.)
Cost 2
Cost 4Cost 4
Cost 4Cost 4
Step 2: Elect a root port for each non-root switch
Decision based on lowest root path cost.
If necessary, ties are broke by upstream BID and port ID values
RP
RP
RP
DP DP
Switch B
Priority 28672
MAC 0000.0c9f.3127
Root Bridge
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Slide 20
How Spanning-Tree Works (Cont.)
Switch A
Priority 28672
MAC 0000.0cab.3274
Switch D
Priority 32768
MAC 0000.0c39.f28a
Switch C
Priority 32768
MAC 0000.0cf6.9370
Cost 2
Cost 4Cost 4
Cost 4Cost 4
F
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FF
Switch B
Priority 28672
MAC 0000.0c9f.3127
Root Bridge
Step 3: Elect a designated port for each segment.
Decision is based on the lowest root path cost.
IF necessary, ties are broken by upstream BID and port ID.
B
B
F
F
F
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Slide 21
How Spanning-Tree Works (Cont.)
Switch A
Priority 28672
MAC 0000.0cab.3274
Switch D
Priority 32768
MAC 0000.0c39.f28a
Switch C
Priority 32768
MAC 0000.0cf6.9370
Cost 2
Cost 4Cost 4
Cost 4Cost 4
RP
RP
RP
DP DP
Switch B
Priority 28672
MAC 0000.0c9f.3127
Root Bridge
Step 4: The ports transition to the forwarding or blocking state.
Root ports and designated ports transition to the forwarding state
Other ports stay in the blocking state
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Slide 22
Versions of Spanning-Tree
IEEE 802.1D: Legacy Spanning-Tree
CST: Assumes one spanning-tree instance for the entire bridged
network, regardless of the number of VLANs
PVST+: A Cisco enhancement of STP that provides a serparate
802.1D spanning-tree instance for each VLAN configured in the
network
802.1w (RSTP): Improves convergence over 1998 STP by adding
roles to ports and enhancing BPDU exchanges
Rapid PVST+: A Cisco enhancement of RSTP using PVST+
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Slide 23
Versions of Spanning-Tree (Cont.)
Protocol Standard Resources
Needed
Convergence Number of
Trees
STP 802.1D Low Slow One
PVST+ Cisco High Slow On for every
VLAN
RSTP 802.1w Medium Fast One
Rapid PVST+ Cisco Very high Fast One for every
VLAN
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Slide 24
Versions of Spanning-Tree (Cont.)
Cisco Catalyst switches have the following
defaults:
PVST
Enabled on all ports
Slower convergence than with RSTP
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Slide 25
PVST+
Forwarding Port for VLAN 1
Blocking Port for VLAN 2
Forwarding Port for VLAN 1
Blocking Port for VLAN 2
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Slide 26
PVST+ (Cont.)
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Slide 27
Changing the Bridge ID
SW1 is not the root bridge for VLAN1. This is the switch that is
connected to FastEthernet0/3 on SW1.
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Slide 28
Changing the Bridge ID
Configures SW1 as the root bridge for VLAN 1
After modification, SW1 is the root bridge for VLAN 1
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Slide 29
Reviewing the STP Topology
Show cdp neighbors
Use STP knowledge
Show spanning-tree vlan
Show spanning-tree vlan
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Slide 30
Reviewing the STP Topology (cont.)
Switch A Switch B:
Root Bridge
Verify the topology
F
F
F
FF
B
B
F
F
F
Switch C Switch D
X
X
VLAN 100
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Slide 31
Reviewing the STP Topology (cont.)
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Slide 32
What if STP Fails?
Switch A
Priority 28672
MAC 0000.0cab.3274
Switch D
Priority 32768
MAC 0000.0c39.f28a
Switch C
Priority 32768
MAC 0000.0cf6.9370
Cost 2
Cost 4Cost 4
Cost 4Cost 4
F
F
F
FF
Switch B
Priority 28672
MAC 0000.0c9f.3127
Root Bridge
B
B
F
F
F
If STP fails for any reason, it fails catastrophically.
X
X
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Slide 33
What if STP Fails? (Cont.)
What if Switch D changed it’s blocking port to forwarding?
Now we have a loop.
Switch A Switch B:
Root Bridge
F
F
F
FF
F
B
F
F
F
Switch C Switch D
X
VLAN 100
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Slide 34
What if STP Fails? (Cont.)
A Bridging Loop is sever
The load on each link will increase, and quickly become overwhelmed
The Switch CPU will max out and become unreachable
Switch A Switch B:
Root Bridge
F
F
F
FF
F
B
F
F
F
Switch C Switch D
X
VLAN 100
Frame enters
here
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Slide 35
PortFast and BPDU Guard
PortFast Characteristics:
moves an Access port to forwarding immediately
Configured only on access ports
BPDU guard characteristics:
If BPDU is received, it will shut down port
Used in a combination with PortFast
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Slide 36
PortFast and BPDU Guard (Cont.)
Configures BPDU guard and PortFast interface FastEthernet0/1
Enables PortFast on all nontrunking interfaces and enables BPDU guard globally for
all PortFast-enabled ports
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Slide 37
PortFast and BPDU Guard (Cont.)
Verifies that PortFast and BPDU guard have been configured on
interface FastEthernet0/1
Verifies that PortFast is enabled on FastEthernet0/1
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Slide 38
Lesson 3
Improving Redundant Switched Topologies with
EtherChannel
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Slide 39
What is EtherChannel
When Multiple links aggregate on a switch, congestion occurs.
One solution is to increase uplink speed, but that solution cannot
scale indefinitely.
Another solution is to multiple uplinks, but loop prevention
mechanisms disable some ports.
xxx
x
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Slide 40
EtherChannel Protocols
Logical aggregation of links between switches
High Bandwidth
Load sharing across links
Viewed as one logical port to STP
Redundancy
xEtherChannel
EtherChannel
EtherChannel
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Slide 41
EtherChannel Protocols (Cont.)
Two protocols exist to negotiate EtherChannel creation
and maintenance:
PAgP is a Cisco proprietary protocol.
LACP is an IEEE 802.3ad standard.
Static EtherChannel can be configured without PAgP or LACP
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Slide 42
EtherChannel Protocols (Cont.)
PAgP negotiates EtherChannel formation and maintenance
On: Channel member without negotiation
PAgP Modes:
Desirable: Actively asking if the other side can or will participate
Auto: Passively waiting for other side
PAgP
Channel establishment On Desirable Auto
On YES NO NO
Desirable NO YES YES
Auto NO YES NO
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Slide 43
EtherChannel Protocols (Cont.)
LACP negotiates EtherChannel formation and maintenance
On: Channel member without negotiation (no protocol).
LACP Modes:
Active: Actively asking if the other side can or will participate
Passive: Passively waiting for other side
LACP
Channel establishment On Desirable Auto
On YES NO NO
Active NO YES YES
Passive NO YES NO
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Slide 44
How to Configure EtherChannel
Interfaces within an EtherChannel must have the same
configuration
Speed/duplex
Trunk or access mode
Same native VLAN
Same allowed VLANs for Trunks
Same Access VLANs for access ports
LACP
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Slide 45
How to Configure EtherChannel (Cont.)
SW1 SW2
Fa0/1
Fa0/2
Fa0/4
Fa0/5
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Slide 46
Verify EtherChannel
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Slide 47
Verify EtherChannel (Cont.)
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Slide 48
Verify EtherChannel (Cont.)
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Slide 49
Lesson 4
Understanding Layer 3 Redundancy
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Slide 50
Why have Default Gateway Redundancy
Server 10.9.1.50
Router B 10.1.10.3Router A 10.1.10.2
No Default GatewayI can’t get to my
Gateway
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Slide 51
Default Gateway Redundancy
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Slide 52
Default Gateway Redundancy (Cont.)
Forwarding
Router
Standby
Router
Link or device failure: The roles
of standby and forwarding router
are reversed
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Slide 53
FHRP
The idea of FHRP is to provide redundancy at
Layer 3
The common protocols that are used are:
HSRP – Cisco proprietary
VRRP – Similar, but an open standard
GLB – Also Cisco proprietary
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Slide 54
HSRP
Hot Standby Routing Protocol
This solution is designed for two routers to represent
themselves as a single “virtual” router
For those end systems on a segment, they see a
single default gateway to access the network
The routers then elect an active router to forward
traffic
If that active router fails, then the one that is in standby mode
will take over
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Slide 55
HSRP (Cont.)
Routers are configured in a “standby” group for
each segment
Routers can belong to more than one group to provide
redundancy
The groups are configured per interface
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Slide 56
HSRP (Cont.)
Each router will still have a unique IP address
for the interface
The routers will share a common Virtual IP
address that end systems use as their gateway
The election will be decided by which router has
the highest priority, or the highest IP address
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Slide 57
HSRP (Cont.)
The failover will occur based on:
If the active router completely fails
If the active router is tracking an interface that fails
If the “hello” messages are no longer received
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Slide 58
HSRP Configuration
Standby “group”
Priority
Standby ip
Preempt
Track
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Slide 59
Introducing HSRP
HSRP defines a group of routers – one active and one standby.
They share a virtual IP and MAC address for use by hosts as their
default gateway
To verify HSRP state, use the show standby command.
HSRP is Cisco proprietary, and VRRP is a standard protocol.
HSRP Group 1
StandbyActive Virtual
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Slide 60
HSRP (Cont.)
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Slide 61
HSRP (Cont.)
Active Router:
Responds to the default gateway,
ARP requests with the virtual router
MAC address
Sends hello messages
Assumes the forwarding of all
packets for the Virtual Router
Knows the virtual router IP
Standby Router:
Listens for the periodic hello’s
Assumes active forwarding of
packets if it does not hear from
active router
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Slide 62
HSRP Track Interface
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Slide 63
HSRP Load Balancing
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Slide 64
Gateway Load Balancing Protocol
Allows full use of resources on
all devices without the
administrative burden of creating
multiple groups
Provides a single virtual IP
address and multiple virtual MAC
address
Routers traffic to single gateway
distributed across routers
Automatically can re-route traffic
on a tracked failure
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Slide 65
Gateway Load Balancing Protocol (Cont.)
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Slide 66
Gateway Load Balancing Protocol (Cont.)
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Slide 67
QoS
Quality of Service
Many applications will suffer at having poor service,
such as VoIP
Latency
Jitter
Dropped packets
Congestion
QoS tries to prioritize these application’s
packets for better service
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Slide 68
QoS
Give certain traffic precedence for delivery over
less important traffic
Best used for networks that have contention or
congestion of packets being delivered
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Slide 69
QoS Configuration
Time sensitive traffic must be identified
Class-mapping
Then this traffic must be marked for importance
Policy-mapping
Then this policy is placed on the outgoing
interface
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Slide 70
QoS Options
Precedence
Shaping
Policing
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Slide 71
Marking
CoS – Layer 2 on ethernet
ToS – Layer 3 IP/IPv6 packet
DSCP – Layer 3 – more detailed than ToS
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Slide 72
Queuing Methods
Class-based WFQ
LLQ – usually called the best practice
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Slide 73
Congestion Avoidance
Tail drop
Weighted Random Early Detection
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Review Questions:
1. QoS provides prioritization for different types of traffic. One goal is to reduce
latency of traffic flows. Which of the following applications are always given a
higher priority to reduce latency?
A. VoIP
B. FTP
C. HTTP
D. Video
E. A & B
F. B & D
G. A & D
2. To configure any protocol/packet for priority, the router must first know what is to
be matched. What configuration command will tell the router what to match?
A. Policy-map
B. Class-map
C. Service-policy
D. NBAR
3. Which of the following is a packet marking?
A. FTP
B. DSCP
C. MPLS
D. HTTP
4. What configuration construct is used to set the marking and priority of packets
matched by a class-map?
A. Service-policy
B. Policy-map
C. DSCP
D. ToS
5. At what layer of the OSI is the use of FHRP going to provide redundancy?
A. Layer 1
B. Layer 2
C. Layer 3
D. Layer 4
6. For two routers to be redundant, using HSRP, the routers will need some
common configuration on each of their interfaces. What at minimum should be
configured the same on each router's interface?
A. Interface IP
B. Standby IP
C. Standby group number
D. Standby priority
E. A & B
F. B & C
G. C & D
7. What must be configured for a router to take the "ACTIVE" role in an HSRP
standby group? Specifically, what setting allows you to choose the router to be
ACTIVE?
A. Standby group number
B. Track interface
C. Standby group IP
D. Standby group priority
8. The router that was ACTIVE in an HSRP group failed, and then the role of
ACTIVE moved to what was the STANDBY router. When the original router
comes back online it will not retake the role of ACTIVE, unless you've configured
what?
A. Standby priority
B. Standby preempt
C. Standby refresh
D. Standby IP
9. What do VLANs create?
A. Broadcast domains
B. Subnets
C. Collision domains
D. WAN connections
10. What type of Switchport will carry all tagged VLAN traffic by default?
A. Access
B. Trunk
C. Routed
D. Serial
Answer Key:
1. G
Voice over IP and video will greatly suffer if they have more than 150ms latency.
Any more, and these applications will generally be unusable.
2. B
The class-map construct allows you to list those protocol/packets that are to be
matched. This does not configure the priority.
3. B
Differentiated Services Code Point is a method of marking a packet for higher
priority. For example, VoIP will be marked with "EF" or expedited forwarding.
4. B
The policy-map is used to set priority and markings for packets matching
specified class-maps.
5. C
These are a collection of redundancy protocols used by Layer 3 devices, such as
routers.
6. F
These routers will have to be in the same standby group, and must agree on
what their virtual IP (VIP) is going to use.
7. D
To specify which router will be the ACTIVE router, you must configure it with a
higher priority value when compared to the STANDBY router.
8. B
A router will not retake the ACTIVE role, unless it's been configured with
preempt.
9. A
A VLAN will create a new broadcast domain, which may or may not be a part of a
new subnet.
10. B
Trunk ports connect switches to each other and by default will carry all tagged
and untagged traffic.