Interconnecting Cisco Networking Devices Part 2 (ICND2) Course 01 - Implementing Scalable Medium-Sized Networks

Transcription

1 Interconnecting Cisco Networking Devices Part 2 (ICND2) Course 01 - Implementing Scalable Medium-Sized Networks

2 Slide 1 Lesson 1 Troubleshooting VLAN Connectivity

3 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 lexibility in designing a network

4 Slide 3 How to Create a VLAN Adds VLAN 2 and names it switchlab99 Assigns interface astethernet 0/2 to VLAN 2

5 Slide 4 How to Create a VLAN (Cont.) Displaying VLAN information

6 Slide 5 What is a Trunk A Trunk can carry traffic for multiple VLANs

7 Slide 6 How to Configure a Trunk Create a trunk from interface configuration mode Configure the a0/11 interface as a VLAN trunk The native VLAN is changed to VLAN 99

8 Slide 7 How to Configure a Trunk (Cont.) Verifies switchport settings on astethernet0/11 Verifies that astethernet0/11 is trunking

9 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 Dynamic Auto Dynamic Desirable Trunk Access Access Trunk Trunk Access Trunk Trunk Trunk Access Trunk Trunk Trunk Trunk Limited Connectivity Access Access Access Limited Connectivity Access

10 Slide 9 VLAN Troubleshooting Show vlan Show mac address-table Show vlan Show interfaces Show interfaces switchport Yes Yes No No

11 Slide 10 VLAN Troubleshooting (Cont.)

12 Slide 11 VLAN Troubleshooting (Cont.)

13 Slide 12 Troubleshooting Trunks Show interfaces trunk Show interfaces trunk Yes Yes No No

14 Slide 13 Troubleshooting Trunks (Cont.)

15 Slide 14 Lesson 2 Building Redundant Switched Topologies

16 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.

17 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

18 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

19 Slide 18 How Spanning-Tree Works (Cont.) Step 1: Elect a Root Bridge Decision based on lowest BID Switch A Priority MAC cab Gbs Switch B Priority MAC c9f.3127 Root Bridge 1Gbs 1Gbs Switch C Priority MAC cf Gbs 1Gbs Switch D Priority MAC c39.f28a

20 Slide 19 How Spanning-Tree Works (Cont.) 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 Switch A Priority MAC cab.3274 RP DP Cost 2 DP Switch B Priority MAC c9f.3127 Root Bridge Cost 4 Cost 4 Cost 4 Cost 4 RP Switch C Priority MAC cf RP Switch D Priority MAC c39.f28a

21 Slide 20 How Spanning-Tree Works (Cont.) Step 3: Elect a designated port for each segment. Decision is based on the lowest root path cost. I necessary, ties are broken by upstream BID and port ID. Switch A Priority MAC cab.3274 Cost 2 Switch B Priority MAC c9f.3127 Root Bridge Cost 4 Cost 4 B Cost 4 Cost 4 Switch C Priority MAC cf B Switch D Priority MAC c39.f28a

22 Slide 21 How Spanning-Tree Works (Cont.) 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 Switch A Priority MAC cab.3274 RP DP Cost 2 DP Switch B Priority MAC c9f.3127 Root Bridge Cost 4 Cost 4 Cost 4 Cost 4 RP Switch C Priority MAC cf RP Switch D Priority MAC c39.f28a

23 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+

24 Slide 23 Versions of Spanning-Tree (Cont.) Protocol Standard Resources Needed Convergence STP 802.1D Low Slow One Number of Trees PVST+ Cisco High Slow On for every VLAN RSTP 802.1w Medium ast One Rapid PVST+ Cisco Very high ast One for every VLAN

25 Slide 24 Versions of Spanning-Tree (Cont.) Cisco Catalyst switches have the following defaults: PVST Enabled on all ports Slower convergence than with RSTP

26 Slide 25 PVST+ orwarding Port for VLAN 1 Blocking Port for VLAN 2 orwarding Port for VLAN 1 Blocking Port for VLAN 2

27 Slide 26 PVST+ (Cont.)

28 Slide 27 Changing the Bridge ID SW1 is not the root bridge for VLAN1. This is the switch that is connected to astethernet0/3 on SW1.

29 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

30 Slide 29 Reviewing the STP Topology Show cdp neighbors Use STP knowledge Show spanning-tree vlan Show spanning-tree vlan

31 Slide 30 Reviewing the STP Topology (cont.) Verify the topology Switch A Switch B: VLAN 100 Root Bridge Switch C B X X B Switch D

32 Slide 31 Reviewing the STP Topology (cont.)

33 Slide 32 What if STP ails? If STP fails for any reason, it fails catastrophically. Switch A Priority MAC cab.3274 Cost 2 Switch B Priority MAC c9f.3127 Root Bridge Cost 4 Cost 4 Switch C Priority MAC cf B X Cost 4 Cost 4 X B Switch D Priority MAC c39.f28a

34 Slide 33 What if STP ails? (Cont.) What if Switch D changed it s blocking port to forwarding? Now we have a loop. Switch A Switch B: VLAN 100 Root Bridge B X Switch C Switch D

35 Slide 34 What if STP ails? (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: VLAN 100 Root Bridge rame enters here B X Switch C Switch D

36 Slide 35 Portast and BPDU Guard Portast 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 Portast

37 Slide 36 Portast and BPDU Guard (Cont.) Configures BPDU guard and Portast interface astethernet0/1 Enables Portast on all nontrunking interfaces and enables BPDU guard globally for all Portast-enabled ports

38 Slide 37 Portast and BPDU Guard (Cont.) Verifies that Portast and BPDU guard have been configured on interface astethernet0/1 Verifies that Portast is enabled on astethernet0/1

39 Slide 38 Lesson 3 Improving Redundant Switched Topologies with EtherChannel

40 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. x x x x

41 Slide 40 EtherChannel Protocols Logical aggregation of links between switches High Bandwidth Load sharing across links Viewed as one logical port to STP Redundancy EtherChannel EtherChannel x EtherChannel

42 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

43 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

44 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

45 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

46 Slide 45 How to Configure EtherChannel (Cont.) a0/1 a0/4 SW1 a0/2 a0/5 SW2

47 Slide 46 Verify EtherChannel

48 Slide 47 Verify EtherChannel (Cont.)

49 Slide 48 Verify EtherChannel (Cont.)

50 Slide 49 Lesson 4 Understanding Layer 3 Redundancy

51 Slide 50 Why have Default Gateway Redundancy Router A Router B Server I can t get to my Gateway No Default Gateway

52 Slide 51 Default Gateway Redundancy

53 Slide 52 Default Gateway Redundancy (Cont.) Standby Router orwarding Router Link or device failure: The roles of standby and forwarding router are reversed

54 Slide 53 HRP The idea of HRP 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

55 Slide 54 HSRP Hot Standby Routing Protocol This solution is designed for two routers to represent themselves as a single virtual router or 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

56 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

57 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

58 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

59 Slide 58 HSRP Configuration Standby group Priority Standby ip Preempt Track

60 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 Active Virtual Standby

61 Slide 60 HSRP (Cont.)

62 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

63 Slide 62 HSRP Track Interface

64 Slide 63 HSRP Load Balancing

65 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

66 Slide 65 Gateway Load Balancing Protocol (Cont.)

67 Slide 66 Gateway Load Balancing Protocol (Cont.)

68 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

69 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

70 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

71 Slide 70 QoS Options Precedence Shaping Policing

72 Slide 71 Marking CoS Layer 2 on ethernet ToS Layer 3 IP/IPv6 packet DSCP Layer 3 more detailed than ToS

73 Slide 72 Queuing Methods Class-based WQ LLQ usually called the best practice

74 Slide 73 Congestion Avoidance Tail drop Weighted Random Early Detection

75

76 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. TP C. HTTP D. Video E. A & B. 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. TP 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 HRP going to provide redundancy? A. Layer 1 B. Layer 2 C. Layer 3 D. Layer 4

77 6. or 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. 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

78 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. or example, VoIP will be marked with "E" 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. 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.