This chapter uses an example network to illustrate hardware configuration problems and configuration troubleshooting. The example network describes the most common connections you need to troubleshoot, and enables you to apply your own enterprise network configuration to the examples.
In a well-formed hierarchical network, there are three easily defined layers, traditionally referred to as the access, distribution, and core layers.
In an enterprise network, each layer provides different functions. Because these layers are not always recognized by their traditional names, the names have been modified to access or workgroup, distribution or policy, and core or backbone.
The access or workgroup layer connects users. Other functions of this layer are shared bandwidth, switched bandwidth, MAC-layer filtering, and micro segmentation. LAN switches, such as the Catalyst 5000 and Catalyst 6000 family of switches, exist most commonly in this layer of the network.
The distribution or policy layer performs the complex, CPU-intensive calculations such as filtering, access lists, inter-VLAN routing, Group Multicast Protocol (GMP), broadcast and multicast domain definition, and address or area aggregation. This layer might also contain the local servers. Routers, switch routers, and occasionally LAN switches reside in the distribution layer.
The core or backbone layer is the backbone of the network. It is high-speed and concerned with quick traffic switching. It does not get involved in expensive packet manipulation. In the following example network, ATM connections function together as the core backbone, and Fast Ethernet and Gigabit Ethernet connections function together as the redundant backbone core. The central servers might also be attached to the high-speed backbone in the core. Switch routers, high-speed routers, and occasionally LAN switches can be found in the core.
Example Networks
This section includes the following example networks:
This section uses a fictitious network to describe actual problems in troubleshooting ATM switched networks.
Figure 4-1 provides a high level overview of the campus and remote networks.
Figure 4-1 Example Network Overview
The example network in Figure 4-1 has the following components:
A campus network of four 10-story buildings
A remote sales building
A telecommuter
4,000 employees on campus
4 buildings with 1,000 employees per building
5,000 total ports
Microsoft NT servers and IP as the primary protocol
Dynamic Host Configuration Protocol (DHCP) used to automatically allocate IP addresses to clients
Approximately 100 users per Catalyst 5000 or Catalyst 5500 switch. This example network requires approximately 50 Catalyst 5000 or Catalyst 5500 switches:
One intermediate equipment closet per building that connects buildings with the ATM distribution switch routers
Fiber-optic connections between wiring closets and intermediate equipment closets
One-half of the users are on VLAN 2; the other half are on VLAN 3
Network 10.0.0.0 255.255.255.0
254 hosts per subnet
Spanning tree and root bridges enabled
No single point of failure
Workgroup servers that are connected using either ATM or Fast Ethernet in Layer 2
Enterprise servers (e-mail, Web, and meeting scheduling) located in the administration building with the edge routers and firewall protection
Switch routers that provide the following:
155-Mbps unshielded twisted-pair (UTP) Optical Carrier 3 (OC-3) connections to servers and high-bandwidth users (computer-aided design [CAD], video, and voice) to the backbone
2,488-Mbps single-mode fiber (OC-48) connections to the core between buildings in the intermediate wiring closets creating the backbone
T3 coaxial connections to the WAN
Catalyst 5000 or Catalyst 600 family LAN switches provide the following:
Access and workgroup connection to individual users of the network
Workgroup server connections
Spanning-tree loop protection and network redundancy
The remote site switch router has the following:
500 employees
750 total ports
The telecommuter router has the following:
Dialup connections
ISDN
Frame Relay
Physical Connections
The example network contains the following physical connections:
155-Mbps UTP—Using permanent virtual path (PVP) and LAN emulation (LANE), connect distribution switch routers to Catalyst 5000 or Catalyst 6000 family LAN switches
622-Mbps multimode fiber and single-mode fiber —Using PVP, connect core switch routers with tag switching enabled
T1 or E1—Using PVPs, connect to the WAN to reach remote sites such as WWW, FTP, Telnet, and e-mail
T3 or E3—Using PVPs, connect to the WAN to reach remote sites such as WWW, FTP, Telnet, and e-mail
T1 circuit emulation switch—Using PVP, connect to private branch exchange (PBX) or using switched virtual circuit (SVC), connect to coder/decoder (CODEC) for constant bit rate (CBR) video
25 Mbps—Connect to computer-aided design/computer-aided manufacturing (CAD/CAM) using a soft permanent virtual circuit (soft PVC) that provides the following QoS:
10 Mbps: video
5 Mbps: audio
5 Mbps: unspecified bit rate (UBR) for data
Frame Relay—Using PVC, connect to a telecommuter
Virtual Connections
The example network in Figure 4-2 has the following virtual connections:
PVPs—Connections between buildings
PVP tunnels—Connect to the remote site through the public network to avoid signalling
SVCs—Connect to nodes that require longer data exchanges but infrequent connections (for example, e-mail server, CAD/CAM connections)
PVC—Connect to nodes that need quick, short access without signalling delay (for example, Domain Name System [DNS] server connections)
Soft PVC—Connect to the UNIX network interface cards (NICs) that do not support signalling (for example, SGI workstations)
LAN emulation (LANE), which has the following connection types:
LAN emulation client (LEC)—Typical application from Catalyst 5000 and Catalyst 5500 to the switch router
LAN emulation configuration server/broadcast and unknown server (LECS/BUS)—Configure on a low-usage switch router, because the application is very route processor intensive
Tag switching—Connect all core switches
Figure 3-2 shows the equipment overview of the example network, including the connection types of the network.
Figure 4-2 Equipment Overview of the Example ATM Network
The engineering building in Figure 4-3 shows the following connections:
622-Mbps single-mode fiber connections between the ATM core switch router on Floor 1 and the campus backbone
T1 CES access connection to CBR and QoS video CODEC for the video conference room
155-Mbps UTP SVC connections from the access switch router to the enterprise servers
155-Mbps UTP, multimode fiber, or single-mode fiber LANE SVC connection from distribution ATM switch routers in each wiring closet to Fast Ethernet access switch routers
Figure 4-3 Engineering Building ATM Connections
The typical Floor 1 wiring closet in Figure 4-4 shows the following connection examples:
622-Mbps single-mode fiber ATM core switch router connections to the backbone
25-Mbps port adapter providing 12 PVC access connections to CAD/CAM users with SGI workstations whose NICs do not support signalling
T1 CES connection access connections to CBR and QoS video CODEC
155-Mbps UTP connection through LANE SVC to Fast Ethernet access switch router
Note Each Fast Ethernet distribution switch connection has a redundant link. (See
Figure 4-4.)
Figure 4-4 Typical Floor 1 ATM Wiring Closet
The typical core switch router configuration in Figure 4-5 shows the following connections:
622-Mbps single-mode fiber core connection through PVC for Private Network-Network Interface (PNNI) redundancy to other buildings
155-Mbps single-mode and multimode fiber distribution connection through PVC to ATM distribution switch routers within the building
The typical distribution switch router configuration in Figure 4-6 shows the following connections:
155-Mbps UTP distribution connection through PVC PNNI between core switch routers
155-Mbps UTP distribution connection through LANE SVCs to the Cisco Systems Catalyst 5000 switches running LECS/BUS
155-Mbps UTP access connection through ELAN SVCs to individual servers
155-Mbps UTP or multimode fiber access connection through SVC with a CBR connection to CODEC for videoconferencing
Figure 4-6 Typical Distribution Switch Router ATM Configuration to Floor 1
The administration building configuration in Figure 4-7 shows the following connections:
155-Mbps UTP connections using LANE SVC connections to e-mail servers, for example, that allow "bursty" traffic requiring signalling and less frequent use
155-Mbps UTP connections using PVC connections to DNS servers, for example, that allow short duration connections without signalling
T3 connection to WAN with access filtering to Hypertext Transfer Protocol (HTTP) and other users
155-Mbps UTP connection to edge router or default gateway with ATM Interface Processor (AIP) installed and tag switching enabled
T1 CES connection to PBX
Video CBR using LANE SVC connections and T1 CES port adapters providing multicast connections to selected users
Soft PVC from source video connection to a destination at a remote site
PVP tunnel to the remote sales building
Frame Relay PVC to the telecommuter
Figure 4-7 Administration Building ATM Connections
Example Mixed ATM and Layer 3 Network
This section uses the fictitious network described in the "Example ATM Network" section to illustrate actual problems in troubleshooting a mixed ATM and Layer 3 switched network.
While the example network overview is the same as shown in Figure 4-1, there are additional redundant Layer 3 Gigabit Ethernet connections between buildings, LAN switches, and some high-usage servers. These redundant Gigabit Ethernet and Gigabit EtherChannel provide the high-capacity trunks needed to connect these gigabit switches if the primary ATM connections should fail.
Physical Connections
The example network contains the following physical connections:
Gigabit Ethernet—Connect distribution Layer 3 switch routers to Catalyst 5000 or Catalyst 6000 family switches
T1 or E1—Using PVPs, connect to the WAN to reach remote sites such as WWW, FTP, Telnet, and e-mail
T3 or E3—Using PVPs, connect to the WAN to reach remote sites such as WWW, FTP, Telnet, and e-mail
T1 circuit emulation switch—Using PVPs, connect to private branch exchange (PBX) or, using switched virtual circuit (SVC), connect to coder/decoder (CODEC) for constant bit rate (CBR) video
Frame Relay—Using PVC, connect to a telecommuter
Virtual Connections
The example network in Figure 4-8 has the following virtual connections:
PVP tunnels—Connect to the remote site through the public network to avoid signalling
T1 CES access connection to CBR and QoS video CODEC for the video conference room
Figure 4-8 shows the equipment overview of the example network, including the connection types of the network.
Figure 4-8 Equipment Overview of the Example Mixed Layer 3 and ATM Network
The engineering building in Figure 4-9 shows the following connections:
Gigabit Ethernet single-mode fiber connections between the ATM core switch router on Floor 1 and the campus backbone
T1 CES access connection to CBR and QoS video CODEC for the video conference room
Gigabit Ethernet UTP SVC connections from the access switch router to the enterprise servers
Gigabit Ethernet UTP, multimode fiber, or single-mode fiber connection from distribution ATM switch routers in each wiring closet to Fast Ethernet access switch routers
Figure 4-9 Engineering Building Layer 3 and ATM Connections
The typical Floor 1 wiring closet in Figure 4-10 shows the following connection examples:
Gigabit Ethernet single-mode fiber ATM core switch router connections to the backbone
T1 CES connection access connections to CBR and QoS video CODEC
Gigabit Ethernet UTP connection to Fast Ethernet access switch
Note Each Gigabit Ethernet distribution switch connection has a redundant link. See
Figure 4-10.
