Load Balancing
The Appropriate Use of VLANs
Given that VLANs are associated so closely with switching, people most often think of what Chapter 14, Campus Design Models, referred to as campus-wide VLANs. Given the popularity of campus-wide VLANs as both a concept and a design, this section discusses its pro and cons, as well as an alternate design for consideration. The popularity of campus-wide VLANs is due in large part to several well-publicized benefits to this approach. First, it can allow direct Layer 2 paths between all of the...
Example 1714 Spanning Tree Configuration
Cat-B2-0B> (enable) set spantree root 20 dia 3 hello 2 VLAN 20 bridge priority set to 8192. VLAN 20 bridge max aging time set to 12. VLAN 20 bridge hello time set to 2. VLAN 20 bridge forward delay set to 9. Cat-B2-0B> (enable) Cat-B2-0B> (enable) set spantree root secondary 21 dia 3 hello 2 VLAN 21 bridge priority set to 16384. VLAN 21 bridge max aging time set to 12. VLAN 21 bridge hello time set to 2. VLAN 21 bridge forward delay set to 9. Cat-B2-0B> (enable) Cat-B2-0B> (enable)...
Figure 141 Multiple IDF Wiring Closets
Given the role that they perform, IDF wiring closets have several specific requirements Port density Because large numbers of end stations need to connect to each IDF, high port density is a must. Cost per port Given the high port density found in the typical IDF, cost per port must be reasonable. Redundancy Because several hundred devices often connect back to each IDF device, a single IDF failure can create a significant outage. Reliability This point is obviously related to the previous...
Figure 23 A Multiport Repeater
A 10BaseT network is comprised of hubs and twisted-pair cables to interconnect workstations. Hubs are multiport repeaters and forward signals from one interface to all other interfaces. As in Figure 2-2, all stations attached to the hub in Figure 2-3 see all traffic, both the good and the bad. Repeaters perform several duties associated with signal propagation. For example, repeaters regenerate and retime the signal and create a new preamble. Preamble bits precede the frame destination MAC...
Example 1717 Full Catalyst Configuration for CatB20B
Begin set password 1 FMFQ HfZR5DUszVHIRhrz4h6V70 set enablepass 1 FMFQ HfZR5DUszVHIRhrz4h6V70 set prompt Cat-B2-0B> set length 24 default set logout 20 set banner motd CPRIVATE NETWORK -- HACKERS WILL BE SHOTM C system set system baud 9600 set system modem disable set system name Cat-B2-0B set system location Building 2 MDF set system contact Joe x111 snmp set snmp community read-only lesspublic set snmp community read-write moreprivate set snmp community read-write-all mostprivate set snmp...
VLANs
This chapter covers the following key topics What is a VLAN Provides a practical and technical definition of virtual LANs. VLAN Types Describes how Layer 2, 3, and 4 switching operate under a VLAN. 802.1Q VLAN Interoperability Describes the IEEE 802.1Q committee's effort to develop a vendor-independent method to create virtual bridged local area networks via shared VLANS (SVLs). Justifying the Need for VLANs Describes how network security, broadcast distribution, bandwidth utilization, network...
Understanding Spanning Tree
The authors would like to thank Radia Perlman for graciously contributing her time to review the material in this chapter. This chapter covers the following key topics What Is Spanning Tree and Why Use Spanning Tree Briefly explains the purpose of the Spanning-Tree Protocol (STP). Explains why some form of loop-prevention protocol is required to prevent broadcast storms and bridge table corruption. Four-Step STP Decision Sequence Describes the process that the Spanning-Tree Protocol uses for...
Bridge Table Corruption
Many switch bridge administrators are aware of the basic problem of broadcast storms as discussed in the previous section. However, fewer people are aware of the fact that even unicast frames can circulate forever in a network that contains loops. Figure 6-4 illustrates this point. Figure 6-4 Without STP, Even Unicast Frames Can Loop and Corrupt Bridging Tables Figure 6-4 Without STP, Even Unicast Frames Can Loop and Corrupt Bridging Tables For example, suppose that Host-A, possessing a prior...
Three STP Timers
The previous section mentioned that a bridge spends 15 seconds in each of the Listening and Learning states by default. In all, the Spanning-Tree Protocol is controlled by the three timers documented in Table 6-5. Time between sending of Configuration BPDUs by the Root Bridge Duration of Listening and Learning states The Hello Time controls the time interval between the sending of Configuration BPDUs. 802.1D specifies a default value of two seconds. Note that this value really only controls...
Example 117 Sample show mls entry Output When Using a Full Flow Mask
Cat-A> (enable) show mls entry Destination IP Source IP Prot DstPrt SrcPrt Destination Mac Vlan -----------MLS-RP 10.0.1.1 10.0.1.2 10.0.2.2 TCP 11778 69 00-00-0c-7c-3c-90 1 2 16 10.0.2.2 10.0.1.3 TCP 110 11004 00-00-0c-5d-0b-f4 2 2 17 10.0.2.2 10.0.1.2 TCP 69 11778 00-00-0c-5d-0b-f4 2 2 17 10.0.1.2 10.0.2.2 TCP 65026 SMTP 00-00-0c-7c-3c-90 1 2 16 10.0.1.3 10.0.2.2 TCP 11002 Telnet 00-60-3e-26-96-00 1 2 15 10.0.1.2 10.0.2.2 TCP 12290 110 00-00-0c-7c-3c-90 1 2 16 10.0.1.2 10.0.2.2 TCP 11266...
Network Diameter Designing with Repeaters in a 100BaseX Network
In a legacy Ethernet system, repeaters extend cable distances, allowing networks to reach further than the segment length. For example, a 10Base2 segment only reaches 185 meters in length. If an administrator desires to attach devices beyond this reach, the administrator can use repeaters to connect a second section of 10Base2 cable to the first. In a 10BaseT network, hubs perform the repeater functions allowing two 100 meter segments to connect together. Legacy repeaters are discussed in more...
Disadvantages of Campus Wide VLANs
There are also some significant downsides to the campus-wide VLANs model Large and overlapping Spanning Tree domains It is easy for a problem in one VLAN to deplete bandwidth in all VLANs across trunk links Many networks using campus-wide VLANs must resort toeliminating all redundancy to achieve network stability Most modern traffic violates the stay in one subnet rule employed by the campus-wide VLAN model Modern routers are not a bottleneck The paragraphs that follow provide more detailed...
Figure 136 IGMP Version 2 Frame Format
IGMP version 2 adds two messages not found in IGMP version 1 to streamline the join and leave process. RFC 2236 added a version 2 membership report and a leave group message. The complete list of messages now consists of the following The membership query and version 1 membership report carry over from IGMP version 1. However, the membership query can now target specific multicast groups. In version 1, the query message is a general query with the group address set to 0.0.0.0. All active groups...
Figure 728 Mdf Mst Switch Load Balancing
Part A in Figure 7-28 illustrates the tunneling process of PVST+ BPDUs through an MST switch (this is used for VLANs other than VLAN 1). Because the MST switch floods the PVST+ BPDUs out all inter-switch ports (assuming that the requirement of all ports Forwarding is met), it is as though the MST switch does not exist. An interesting consequence of this is that the left path appears to only have a cost of 19, whereas the right path has the usual cost of 38 (19+19). In other words, Cat-A, the...
Wrong Motives for Using VLANs
One common motivation for using VLANs tends to get network administrators excited about VLANs. Unfortunately, reality quickly meets enthusiasm revealing errors in motivation. The advent of VLANs led many to believe that life as a network administrator would simplify. They thought that VLANs would eliminate the need for routers, everyone could be placed in one giant flat network, and they could go home at 5 00 PM each evening like everyone else in their office. Wrong. VLANs do not eliminate...
When to Use ATM
Although ATM has enjoyed considerable success within the marketplace, the debate continues which is better ATM or competing technologies such as Gigabit Ethernet in the campus and Packet Over SONET in the WAN Well, like most other issues in the internetworking field, the answer is it depends. Specifically, ATM has distinct advantages in the following areas Full support for timing-critical applications Full support for Quality of Service (QoS) Communication over long geographic distances...
Figure 95 Vpivci Usage in an ATM Network
The NY router uses a single physical link connected to Port 0 on the NY ATM switch carrying both virtual circuits. How, then, does the ATM switch know where to send each cell It simply makes decisions based on VPI VCI values placed in ATM cell headers by the router. If the NY router (the ATM edge device) places the VPI VCI value 0 50 in the cell header, the ATM switch uses a preprogrammed table indicating that the cell should be forwarded out Port 2, sending it to LA. Also, note that this table...
Keep and Maintain Network Documentation
One element for any troubleshooting philosophy to work is frequently absent documentation. Many administrators neglect to document their network, or if they do, they do not keep the documentation up to date. Documentation provides the framework to answer fundamental questions such as, What changed or What connects to device X or What Layer 2 paths exist from point A to point B Reconstructing the network topology documentation during a crisis does not lend itself to an efficient or structured...
Example 811 show vlan Command Output
Console> (enable) show vlan VLAN Name Status Mod Ports, Vlans------------------ 1 default active 1 1-2 2 1-24 100 VLAN0100 active 110, 120 110 VLAN0110 active 120 VLAN0120 active 500 VLAN0500 active 600 VLAN0600 active 1002 fddi-default active 1003 trcrf-default active 1004 fddinet-default active 1005 trbrf-default active 1003 VLAN Type SAID MTU Parent RingNo BrdgNo Stp BrdgMode Trans1 Trans2--------------------------- 1 enet 100001 1500 ----- 0 0 100 trbrf 100100 4472 - - 0x5 ibm - 0 0 110...
Understanding VTP
VTP is a Cisco proprietary, Layer 2 multicast messaging protocol that can ease some of the administrative burden associated with maintaining VLANs. VTP maps VLANs across all media types and VLAN tagging methods between switches, enabling VLAN configuration consistency throughout a network. VTP reduces manual configuration steps required at each switch to add a VLAN when the VLAN extends to other switches in the network. Further, VTP minimizes potential configuration mismatches and manages the...
One Broadcast Domain
Collision Domain - Broadcast Domain This significant improvement in bandwidth demonstrates why segmenting a LAN benefits users. The same number of users in the network in Figure 2-8 now have more available bandwidth than they did in the network in Figure 2-5. Although switching is discussed later in the chapter, it is valid to comment now that the ultimate bandwidth distribution occurs when you dedicate one user for each bridge interface. Each user then has all of the local bandwidth to...
Figure 88 Using Token Ring Isl Trisl to Transport Token Ring Over an Ethernet Trunk
Unfortunately, Token Ring attributes differ significantly from Ethernet. Differences between Token Ring and Ethernet include the following Frame sizes Token Ring supports frames both smaller and extremely larger than Ethernet. Routing Information Field Token Ring frames can include an RIF which is meaningless in an Ethernet system. Explorer frames Token Ring stations can transmit an explorer frame to discover the relative location of a destination device. This frame type includes a bit...
IP Addressing
Each VLAN utilizes a single IP subnet. Happy Homes will use network 10.0.0.0 with Network Address Translation (NAT) to reach the Internet. The design document calls for the following IP address scheme The subnet mask will be 24 (or 255.255.255.0) for all links. For example, the thirtieth address on the Sales VLAN in Building 1 would be 10.1.11.30. Because HSRP will be in use, three node addresses are reserved for routers on each subnet. The .1 node address is reserved for the shared HSRP...
Example 51 Router on a Stick Configuration File
Interface fastethernet 2 0.1 ip address 172.16.10.1 255.255.255.0 ipx network 100 encapsulation isl 100 interface fastethernet 2 0.2 ip address 172.16.20.1 255.255.255.0 ipx network 200 encapsulation isl 200 interface fastethernet 2 0.3 ip address 172.16.30.1 255.255.255.0 encapsulation isl 300 Example 5-1 sets up a trunk between a device and the router. Trunks and InterSwitch Link (ISL) encapsulation are discussed in more detail in Chapter 8. Trunks allow traffic from more than one VLAN to...
Telnet Configuration
Before you can Telnet to a Catalyst, you need to assign an IP address to the sc0 interface on the Supervisor module. The previous section, Console Configuration, demonstrated how to do this. You can Telnet to a Catalyst as long as your Telnet device can reach the VLAN and IP network that the sc0 interface belongs to. Telnetting to the Catalyst allows you to perform any command as if you were directly attached to the Catalyst console. You do, however, need to know the normal mode and privileged...
Media Independent Interface MII
When you order networking equipment, you usually order the system with a specific interface type. For example, you can purchase a router with a 100BaseTX connection. When you buy it with this kind of interface, the 100BaseTX transceiver is built in to the unit. This connection is fine, as long as you only attach it to another 100BaseTX device such as another workstation, hub, or switch. What if you decide at a later time that you need to move the router to another location, but the distance...
Layer 3 Switching and the Catalyst 60006500s
This chapter covers the following key topics Catalyst 6000 Layer 2 Characteristics Discusses the base Catalyst 6000 and 6500 configuration. MSM Layer 3 Switching The Multilayer Switch Module (MSM) is a router-on-a-stick configuration that provides ASIC-based routing for IP, IPX, and multicast traffic. This section discusses how to configure, use, and deploy these devices. MSFC Hybrid Mode Layer 3 Switching The Multilayer Switch Feature Card (MSFC) Hybrid Mode is an implementation of Multilayer...
Duplicate Ring Protocol DRiP
In a Token Ring environment, each ring has a unique ring number identifying it for source-route bridging. Similarly, in a switched Token Ring, except for the default and backup TrCRFs mentioned earlier, each TrCRF has a unique ring number. If an administrator accidentally misconfigures another TrCRF with the same ring number, shown in Figure 3-11, the Token Ring switching process gets confused. Figure 3-11 Do not attempt this. Duplicate ring numbers are not allowed on multiple switches. Figure...
PVST Mapping and Tunneling
PVST+ utilizes two techniques to provide transparent STP support across the three types of regions Mapping is used between PVST and PVST+ regions. Each Spanning Tree in a PVST region maps to a separate Spanning Tree in PVST+ on a one-to-one basis. The same occurs in the reverse direction. This process is both simple and obvious. On the other hand, when converting between MST and PVST+ regions, both mapping and tunneling must be used. The single Spanning Tree used in the MST region maps to a...
Storeand Forward Switching
The store-and-forward switching mode receives the entire frame before beginning the switching process. When it receives the complete frame, the switch examines it for the source and destination addresses and any errors it may contain, and then it possibly applies any special filters created by the network administrator to modify the default forwarding behavior. If the switch observes any errors in the frame, it is discarded, preventing errored frames from consuming bandwidth on the destination...
Bundling Ports
When bundling ports for EtherChannel using early EtherChannel-capable line modules, you must follow a couple of rules Use contiguous ports for a bundle. All ports must belong to the same VLAN. If the ports are used for trunks, all ports must be set as a trunk. If you set the ports to trunk, make sure that all ports pass the same VLANs. Ensure that all ports at both ends have the same speed and duplex settings. You cannot arbitrarily select ports to bundle. See the following descriptions for...
Fragment Free Switching
Another alternative offers some of the advantages of cut-through and store-and-forward switching. Fragment-free switching behaves like cut-through in that it does not wait for an entire frame before forwarding. Rather, fragment-free forwards a frame after it receives the first 64 octets of the frame (this is longer than the six bytes for cut-through and therefore has higher latency). Fragment-free switching protects the destination segment from fragments, an artifact of half-duplex Ethernet...
Calculating Endto End BPDU Propagation Delay for Max Age
End-to-End BPDU Propagation Delay is the amount of time that it takes for a BPDU to travel from one edge of the network to the other edge of the network. The 802.1D specification assumes that up to three BPDUs can get lost along the way, the maximum distance between any two nodes in the network is seven bridge hops, and each bridge can take up to one second to propagate a BPDU after receiving it. Also, the default Hello Time interval of two seconds is assumed. Table 7-2 documents these...
Advantages of Campus Wide VLANs
As the paragraphs that follow attest, there are some alluring aspects to the flat earth approach. First, the campus-wide VLANs model allows network designers to create a direct Layer 2 path from end stations to the most commonly used servers. By deploying Layer 2 switching in all three layers of the access distribution core model, campuswide VLANs should dramatically increase available bandwidth. The second advantage of the campus-wide VLANs model is that VLANs can be used to provide logical...
Example 41 clear config all Output
Console> (enable) clear config Usage clear config all clear config < mod_num> clear config rmon Console> (enable) clear config all This command will clear all configuration in NVRAM. This command will cause ifIndex to be reassigned on the next system startup. Do you want to continue (y n) n System configuration cleared. Use 'session' command to clear ATM or Router specific configurations. Console> (enable) From the Supervisor console, or via Telnet, you can clear the Catalyst...
Ethernet LANE Frame Format
Ethernet LANE traffic that passes over the Data Direct uses the frame format illustrated in Figure 9-15. Figure 9-15 Ethernet Data Frame Format for LANE Figure 9-15 Ethernet Data Frame Format for LANE If you compare the LANE Version 1.0 format to the traditional Ethernet frame you will notice two changes The addition of the 2-byte LEC ID field As LECs contact the LES, they are assigned a unique, 2-byte LECID identifier. In practice, the first LEC that joins is 1, the second is 2, and so on. The...
Figure 1129 A Logical Representation of a BVI
If interface fa0 0 4 receives a frame with Host-D's MAC address, it bridges it out interface fa0 0 3. However, if Host-D pings Host-A, Host-D sends the IP packet to its default gateway, address 10.1.4.1 (the BVI's address). If necessary, Host-D ARPs for 10.1.4.1 to learn the BVI's MAC address. When interface fa0 0 4 receives the traffic with a MAC address that belongs to the BVI, it knows to route, not bridge, the traffic. The normal routing process then sends the traffic out interface fa0 0 0....
Carrier Sense with Multiple Access with Collision Detection CSMACD
Carrier sense multiple access collision detect (CSMA CD) describes the Ethernet access method. CSMA CD follows rules similar to those in a meeting. In a meeting, all individuals have the right to speak. The unspoken rule that all follows, though, is Only one person can talk at a time. If you have something to say, you need to listen to see if someone is speaking. If someone is already speaking, you must wait until they are finished. When you start to speak, you need to continue to listen in...
Catalyst 6000 Layer 2 Characteristics
In many respects, Catalyst 6000s can be viewed as bigger versions of Catalyst 5000s. This is especially true when Catalyst 6000s are configured to run the traditional Catalyst XDI CatOS images. In this case, Catalyst 6000s use exactly the same user interface discussed in Chapter 4. Virtually every feature discussed throughout the book is supported using the same configuration steps on both products. In short, Layer 2 Catalyst 6000s look completely familiar to anyone who has configured a...
Troubleshooting Philosophy 2 Evaluate Layers of the OSI Model
The other troubleshooting philosophy looks at problems according to the OSI model that divide network technology into identifiable components. As you identify problems at each of the layers, you will find that you can place them into one of the three buckets discussed in the previous section. You can, for example, look at the physical layer. Problems at the physical layer relate to cables and media. Is there too much cable Not enough Did you connect the cable into the correct port Clearly these...
Figure 154 A Split Layer 2 Core
In this case, the key to creating a fast-converging and resilient core is to actually partition the core into two separate VLANs and not cross-link the switches to each other. The first core VLAN is used for the pair of switches on the left, and the second VLAN is used for the pair of switches on the right. If the core switches in Figure 15-4 were cross-linked or fully meshed and a single VLAN were deployed, Spanning Tree convergence and load balancing issues would become a problem. Finally,...
Token Ring Components
Token Ring systems use a hub architecture to interconnect stations. The hub, called a multistation access unit (MAU), creates a logical ring from the star attached stations as shown in Figure 1-13. Figure 1-13 Token Ring Stations Attached to an MAU Figure 1-13 Token Ring Stations Attached to an MAU Internal to the MAU, the transmit from one station connects to the receive of another station. This continues between all attached stations until the ring is completed. What happens if a user...