dSiiaiVT

1Chapter 10 Objectives
2The CCNA Topics Covered in this chapter include:
3What is layer-2 switching
4Switching services
5Bridges vs. LAN switching
6Three switch functions
7MAC table
8Switching loops Spanning-Tree Protocol (STP)
9Configuring Catalyst Switches
10
11
12Purposes for using switching
13Breaks up collision domains
14Cost-effective, resilient internetwork
15Purpose for Spanning-Tree Protocol (STP)
16Stops loops in layer 2 switched networks
17
18Switch
19The hub is a simple device that transmits an incoming frame out all the other ports on the hub
20The switch has intelligence and can filter out and forward frames based on their NIC address
21A switch maintains internal port table(s) that keep track of which frames arrived on which ports
22A switch observes each frame that arrives at a port, extracts the source address from the frame, and places that address in the port’s routing table
23Switches have eliminated many hubs
24Workstations that connect to a hub are on a shared segment
25Workstations that connect to a switch are on a switched segment
26
27The backplane of a switch is fast enough to support multiple data transfers at one time In a fully switched network, switches replace all the hubs of an Ethernet network with a dedicated segment for every node. 
28Multiple workstations connected to a switch use dedicated segments
29This is a very efficient way to isolate heavy users from the network - fast
30Can allow simultaneous access to multiple servers, or multiple simultaneous connections to a single server
31
32The only devices on each segment are the switch and the node, the switch picks up every transmission before it reaches another node. The switch then forwards the frame over the appropriate segment.
33 Switching allows a network to maintain full-duplex Ethernet. Before switching, Ethernet was half-duplex, which means that data could be transmitted in only one direction at a time. This full-duplex connection helps to eliminate collisions
34In a fully switched network, each node communicates only with the switch, not directly with other nodes. Allow for simultaneous transmission and reception of data to and from a workstation
35To support a full-duplex connection to a switch, at least two pairs of wires are necessary
36One for the receive operation 
37One for the transmit operation
38Most people install four pairs today, so wiring is not the problem
39
40Whether shared or dedicated segments are involved, the primary goal of a switch is to isolate a particular pattern of traffic from other patterns of traffic or from the remainder of the network 
41Switches, because of their backplane, can also allow multiple paths of communications to simultaneously occur
42
43EtherChannel is a port link aggregation technology or port-channel architecture used primarily on Cisco switches. It allows grouping of several physical Ethernet links to create one logical Ethernet link for the purpose of providing fault-tolerance, high bandwidth  and high-speed links between devices
44Load shares across the links and viewed as one STP port, no loops
45
46
47
48
49lS1#config tS1(config)#int port-channel 1S1(config-if)#int range f0/1-2S1(config-if-range)#switchport mode trunkS1(config-if-range)#switchport nonegotiateS1(config-if-range)#channel-group 1 mode desirable
50
51Most Ethernet LAN switches use a system called transparent bridging to create their address lookup tables. 
52Transparent bridging is a technology that allows a switch to learn everything it needs to know about the location of nodes on the network 
53Transparent bridging has five components:
54	•	Learning 
55	•	Flooding 
56	•	Filtering 
57	•	Forwarding 
58	•	Aging
59
60
61Transparent Bridging on Switches
62
63Spanning Tree
64As good as switches are in a network, they can also be problematic. Need to safeguard by using STP.
65
66First, it prevents problems caused by loops on a network. Second, when redundant loops are planned on a network, STP deals with remediation of network changes or failures. On by default in switches
67The Layer 2 protocol used by LAN switches to locate and eliminate redundant paths is called the Spanning Tree Protocol (STP). STP is a Layer 2 protocol that passes data back and forth to find out how the switches are organized on the network and then takes all the information it gathers and uses it to create a logical tree. Part of the information STP receives defines exactly how all the network switches are interconnected.
68If there are 2 paths, switches need to continually understand the topography of the network, even though only one is actually forwarding messages. And both switches need to have some way to understand which is the primary one. 
69To do this, they have a separate path connection just between the switches in which they exchange information, using bridge protocol data units (BPDUs).
70
71
72Why STP?
73Remember, when unknown packets first arrive into switches, the switch needs
74      to broadcast that packet to all other switches, causing 
75     “broadcast storms that can clog the network”
76The storm is caused because switches will continue to update their MAC address table
77Duplicate frames sent all over the place
78
79Avoid loops?
80Broadcasts go out on all ports so you BLOCK a port so that traffic only is transmitted on 1 of the ports
81STP will BLOCK redundant ports – ignore the frames on the block port
82
83
84To prevent broadcast storms and other unwanted side effects of looping, Digital Equipment Corporation created the spanning-tree protocol (STP), which has been standardized as the 802.1d specification by the Institute of Electrical and Electronic Engineers(IEEE). 
85Spanning tree uses the spanning-tree algorithm (STA), which senses that the switch has more than one way to communicate with a node, determines which way is best and blocks out the other path(s). Loop avoidance is created if multiple connections between switches are created for redundancy 
86STP builds this information by sending out network packets called Bridge Protocol Data Units (BPDUs or sometimes BDUs). These BPDUs — or rather the data in them — control the way STP determines the network topology.
87All the switches on the network will send BPDU frames to the entire network, even if a network that does not have any loops. These packets, by default, are sent out on the network every two seconds, are very small, and do not negatively affect the network traffic.
88Once negotiated, the switch with the lowest algorithm result (including MAC address) will become the ROOT bridge
89
90The ports on a switch with the enabled Spanning Tree Protocol (STP) are in one of the following five port states.
91Blocking
92Listening
93Learning
94Forwarding
95Disabled
96
97When a port is enabled, it will go into a transition state as per the below:
98Listening State
99The port is not forwarding traffic and not learning any MAC addresses but listening for BPDUs. Similar to he blocking state.
100Learning State
101The port is not forwarding traffic but is learning MAC addresses. Creating the MAC address table in the switch. 
102Disabled State
103The actual port is in a DOWN state and does not participate in frame forwarding or the operation of STP
104
105Every port will be in an eventual block state or forward state as per the below:
106Blocking State
107A port in the blocking state does not participate in frame forwarding and also discards frames received from the attached network segment. A port that is blocking traffic (except for controlled frames like BPDUs)
108Forwarding State
109The port is sending and receiving traffic as per normal
110
111Because of the amount of time for convergence on these ports, it may cause  slowness between devices
112From blocking to listening: 20 seconds 
113From listening to learning: 15 seconds 
114From learning to forwarding: 15 seconds
115Process tales almost a minute to move through the transition states
116
117Portfast minimizes the time it takes for the server or workstation to come online, thus preventing problems with applications such as DHCP, DNS,  etc.
118The use of Portfast should be implemented when the port on the switch is directly connected to a server/workstation and never to another hub/switch.
119
120How to configure PORTFAST
121
122Switch1>enable
123Switch1#conf t
124Switch1#(config) interface range fa0/3 – 4                       (can install on one or multiple ports0Switch1(config-if-range) switchport mode access           (makes ports  single device – NOT TRUNK)Switch1#(config-if-range) spanning-tree portfast            (allows faster convergence)
125
126Switch1#show run
127interface FastEthernet0/3switchport mode accessspanning-tree portfast!interface FastEthernet0/4switchport mode accessspanning-tree portfast
128
129In order to route we need to know
130The Remote Networks
131Their Neighbor Routers
132All Possible routes to remote network
133The absolute best route to all remote networks
134Maintain and verify the routing information
135
136IP Routing
137Routing involves the delivery of datagrams between end systems located on different networks. 
138Without routers and routing protocols, end host communication would be limited to only those systems on the same physical segment
139Routers provide the physical connection between networks. Routers must be configured with some type of routing protocol to enable communication between hosts beyond their local segments 
140PURPOSE: To facilitate communication between remote hosts
141For hosts to communicate with other hosts located on different networks, end systems must be configured with the IP address of at least one local router (also referred to as the default router/gateway). 
142
143
144If all hosts are attached to the same segment, there is NO need for routers (default gateways) and routing protocols for these hosts to communicate with each other
145
146Router Tables
147All routers must have a local route table. 
148Route tables are built through several input sources, such as directly connected networks, static, default, and dynamic routes. No matter what the source , the table is built
149Routers, after identifying the destination address, use these route tables to determine the best path between source and destination. 
150When a router receives a packet, the destination address is determined and then compared to each route within the route table until an exact or best route match is found. 
151Typically, when more than one path to a destination exists, one path needs to be selected (as the best path/primary) by the routing protocol and placed in the route table. 
152Metrics are used to determine best path
153HOP COUNT, Bandwidth, Load, Delay, Reliability, Cost 
154
155Autonomous systems:
156Autonomous systems are collection of routers and networks within a common administration
157Most routing occurs within logical boundaries referred to as Autonomous Systems (AS), or routing domains and is describe as a collection of related networks, subnets, and routers that use the same routing protocol and share information within the common area 
158In this example, RIP and IGRP would be considered separate routing domains. Each routing domain consists of the routing protocol and the networks, subnets, and routers within this domain and is its’ own Autonomous System.
159
160
161Static vs Dynamic
162Static	
163Uses a route that is manually configured in a router
164Dynamic
165Router learns routes with the use of a routing protocol
166
167Routed vs Routing
168Routing protocols are used between routers to: 
169Determine the path of a packet through a network
170Maintain routing tables
171RIP, EIGRP, OSPF, BGP are examples
172
173Routed protocols are:
174Assigned to an interface with an IP address
175Once the path is determined by the Routing protocol, determines method of delivery
176
177Classful vs Classless Routing
178Classful routing protocols do not send subnet mask information with their routing updates. A router running a classful routing protocol will react in one of two ways when receiving a route:
179If the router has a directly connected interface belonging to the same major network, it will apply the same subnet mask as that interface.
180If the router does not have any interfaces belonging to the same major network, it will apply the classful subnet mask to the route.
181Belonging to same “major network” simply indicates that they belong to the
182same “classful” network. For example:
18310.3.1.0 and 10.5.5.0 belong to the same major network (10.0.0.0)
18410.1.4.5 and 11.1.4.4 do not belong to the same major network
185192.168.1.1 and 192.168.1.254 belong to the same major network (192.168.1.0)
186192.168.1.5 and 192.167.2.5 do not belong to the same major network.
187
188Classful routing protocols do not include the subnet mask with the route advertisement.
189Within the same network, consistency of the subnet masks is assumed.
190Summary routes are exchanged between foreign networks.
191Examples of classful routing protocols:
192RIP Version 1 
193IGRP
194
195Classless routing protocols do send the subnet mask with their updates.
196Thus, Variable Length Subnet Masks (VLSMs) are allowed when using classless routing protocols.
197Examples of classless routing protocols include RIPv2, EIGRP, OSPF,
198
199Usually a good idea to be in a classless state
200To configure your router in “classful” mode:
201Router(config)# no ip classless
202To configure your router in “classless” mode 
203Router(config)# ip classless
204
205Administrative distance is the measure used by Cisco routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. 
206
207Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. A lower numerical value is preferred, e.g. an OSPF route with an administrative distance of 110 will be chosen over a RIP route with an administrative distance of 120.
208
2091. Distance Vector Routing Protocol such as RIP and IGRP/EIGRP
210These are called Distance Vector protocols because they base routing decisions on the “distance” of the remote destination in terms of the number of network layer hops that the packet will have to traverse.
211Periodically passes complete routing tables to neighbors. Routers pass copies of their routing tables and accumulate distance values. In RIP, every 30 seconds.
212
2132. Link State Routing Protocol such as OSPF and IS-IS
214Link state protocols require each router to send the state of its own interfaces to every router in the internetwork.  After all the information is collected, each router, independent of the other routers, calculate best path to all destinations. Updates are sent ONLY when there is a link change, eg, interface down. But significant demand of router processes.
215
2163. Hybrid Routing Protocol such as EIGRP - combination
217
218There are a few routing protocols that can be used to route between routers
219	static routing
220	RIP
221	IGRP/EIGRP
222	OSPF (Open shortest Path First)
223
224Interior Vs Exterior routing
225Some protocols are used to stay within an organization 
226Other protocols are used to share routing between organizations
227Interior Gateway Protocol (IGP) include OSPF, IS-IS, RIP, and EIGRP
228Exterior Gateway Protocol is BGP