Overview of the Catalyst 8510 Campus Switch Router

The Catalyst 8510 places no dependencies on which ports are configured in the channel. The ports can exist on the same or on different line modules in the chassis.

Each line module includes a micro-coded processor that handles all packet forwarding. The main functions of the control layer between the routing protocol and the firmware datapath microcode include:

• Managing the internal data and control circuits for the packet forwarding and control functions

• Extracting the other routing and packet forwarding related control information from the Layer 2 and Layer 3 bridging and routing protocols and the configuration data; then convey the information to the line module to control the datapath

• Collecting the datapath information, such as traffic statistics, from the line module to the switch route processor

• Handling certain data packets sent from the Ethernet line modules to the switch route processor

On any Catalyst 8510 system in the network, the frame and packet scheduling and discarding policies are determined by the class to which the frames and packets belong. For example, the overall service given to frames and packets in the premium class will be better than that given to the standard class; the premium class is expected to experience lower loss rate or delay.

Table 1-1: Catalyst 8510 Layer 1 and Layer 2 Features

Layer 1 Features
100BaseFX full and half duplex
10/100BaseTX full and half duplex with auto-negotiation
Layer 2 Bridging Features
Layer 2 transparent bridging
Layer 2 MAC learning, aging, and switching by hardware
Spanning tree protocol (IEEE 802.1d) support per bridge group
Support for a maximum of 64 active bridge groups
Integrated Routing and Bridging (IRB) mode support
Virtual LAN (VLAN) Features
Inter-Switch Link (ISL)-based VLAN trunking support on Ethernet ports
Fast EtherChannel (FEC) Features
Bundling of up to 4 Fast Ethernet ports
Load sharing based on source and destination IP addresses of unicast packets
Load sharing for bridge traffic based on MAC address
Inter-Switch Link (ISL) support on the Fast EtherChannel

This section describes the notable Layer 2 features supported by the Catalyst 8510 campus switch router.

The ISL frame is a standard Ethernet or IEEE 802.3 frame, tagged with a VLAN ID. The system sends the ISL frame as a multicast, but it is meaningful only to ISL devices. Since it is a standard frame, repeater hubs and transparent bridges forward it as they would any other frame. Any 100 Mbps Ethernet link can support this protocol. The link can run at either half duplex or full duplex.

The Catalyst 8510 supports up to 255 VLANs per system. Because routing will take place, each VLAN is assumed to terminate at the Catalyst 8510. This may not necessarily be the case, so the switch router also supports integrated routing and bridging (IRB). The Catalyst 8510 supports VLAN trunking through Cisco ISL technology.

Each device configured for CDP sends periodic messages to a multicast address. Each device advertises at least one address at which it can receive Simple Network Management Protocol (SNMP) messages.

This section describes the notable Layer 3 features supported by the Catalyst 8510.

CEF manages route distribution and forwarding by distributing routing information from the switch route processor (SRP) to the individual Ethernet line modules. This technology, utilized within the Internet, provides scalability in large campus core networks. CEF provides Layer 3 forwarding based on a topology map of the entire network, resulting in high-speed routing table lookups and forwarding.

One of the key benefits of CEF in the Catalyst 8510 is its routing convergence. Since the forwarding information base (FIB) is distributed to all line modules, whenever a route goes away or is added, the FIB updates that information and provides it to the line modules. Thus, SRP interrupts are minimized. The line modules receive the new topology very quickly and reconverge around a failed link based on the routing protocol being used.

The Cisco IOS software has two load balancing schemes for IP traffic: per-packet load balancing and per-destination load balancing.

Per-packet load balancing allows the router to send data packets over equal-cost paths without regard to the individual end-host or user session. Though packets are evenly distributed in this scheme, they can also get out of order because per-packet load balancing uses a round-robin paradigm.

Per-destination load balancing allows a router to achieve load sharing using equal-cost paths by ensuring that packets for a given destination always take the same path. Note that the path utilization of this scheme might not be as efficient as per-packet load balancing, but the packets cannot be received out of order.

• Per-destination load balancing is enabled by default when the forwarding information base (FIB) is enabled.

• In Cisco IOS software, if you want to enable per-packet load sharing to a particular destination, you must enable per-packet load sharing for all interfaces that can forward traffic to the destination.

• Currently, the FIB supports up to 6 equal-cost paths; the default is 4.

One of the shortcomings of per-destination load balancing, then, is that it does not take into account the source of the packet. If multiple sources (servers) send the IP packets to the same destination, the packets use the same route---even if there are multiple equal-cost paths available.

The implementation of load balancing on the Catalyst 8510 employs a source + destination-based load balancing scheme, which is an enhanced version of the Cisco IOS software per-destination load balancing method. Essentially, this method takes certain bits from the source and destination IP addresses and maps this addressing information into a path. There are two benefits of using this method:

• The traffic is distributed more effectively.

• There is almost no impact on the datapath performance.

This release of the Catalyst 8510 campus switch router supports load balancing for two equal-cost paths. The switch router does not support per-packet load balancing.

Specifically, local or unroutable traffic will be bridged among the bridged interfaces in the same bridge group, while routable traffic will be routed to other routed interfaces or bridge groups.

The Catalyst 8510 supports IRB for IP and IPX only.

Some examples of when to use IRB follow:

• When you want to interconnect a bridged network with a routed network, the IRB feature enables the switch router to act as a true brouter.

For example, when you are migrating a bridged network to a routed network, or when the remote site does not have routing capabilities, you can use the switch router to interconnect the bridged and routed networks.

• When you want to conserve IP or IPX addresses by connecting network segments with bridges and assigning each bridge group one network address.

• When you want to break one big segment into several small segments to increase end stations' performance.

The command interpreter is called the EXEC. You must log into the switch router or switch before you can enter an EXEC command. For security purposes, Cisco IOS software provides two levels of access to commands: user and privileged. The user mode is called user EXEC mode. The privileged mode is called privileged EXEC mode and requires a password.

Table 1-3 describes some of the most commonly used modes, how to enter the modes, and the resulting prompts. The prompt helps you identify which mode you are in and, therefore, which commands are available to you.

Table 1-3: Cisco IOS Command Modes

Command Mode	Usage	How to Enter the Mode	Prompt Display
User EXEC	Allows you to connect to remote devices, change terminal settings on a temporary basis, perform basic tests, and display system information. The EXEC commands available at the user level are a subset of those available at the privileged level.	Log in.	Router>
Privileged EXEC	Sets operating parameters. The privileged command set includes the commands in user EXEC mode, as well as the configure command. Use this command to access the other command modes. Privileged EXEC mode also includes high-level testing commands, such as debug.	From the user EXEC mode, enter the enable command.	Router#
Global configuration	Apply to features that affect the system as a whole.	From the privileged EXEC mode, enter the configure terminal command.	Router(config)#
Interface configuration	Many features are enabled for a particular interface. Interface commands modify the operation of an Ethernet port. You initiate interface configuration with the interface command, which defines the interface type. You can configure several virtual interfaces on a single physical serial interface. These virtual interfaces are logical constructs called subinterfaces.	From global configuration mode, enter the interface type number command. For example, enter interface fa0/0/0 to configure the Fast Ethernet 0/0/0 interface.	Router(config-if)#
Console configuration	From the directly connected console or the virtual terminal used with Telnet, use this configuration mode to configure the console port.	From global configuration mode, enter the line console 0 command.	Router(config-line)#

When you type exit, the switch router backs out one level. In general, typing exit from one of the specific configuration modes returns you to global configuration mode. To exit configuration mode completely and return to privileged EXEC mode, press <Ctrl-Z>.

You can also abbreviate commands and keywords by entering just enough characters to make the command unique from other commands. For example, you can abbreviate the show command to sh.

Router> ?

To obtain a list of commands that begin with a particular character sequence, type in those characters followed immediately by the question mark ( ? ). Do not include a space. This form of help is called word help, because it completes a word for you.

Router# co?
configure connect copy

To list keywords or arguments, enter a question mark in place of a keyword or argument. Include a space before the question mark. This form of help is called command syntax help, because it reminds you which keywords or arguments are applicable based on the command, keywords, and arguments you have already entered.

Router# configure ?
memory Configure from NV memory
network Configure from a TFTP network host
terminal Configure from the terminal

To redisplay a command you previously entered, press the up-arrow key. You can continue to press the up-arrow to see more previously issued commands.

TimeSaver Each command mode restricts you to a subset of commands. If you are having trouble entering a command, check the prompt, and enter the question mark ( ? ) for a list of available commands. You might be in the wrong command mode or using incorrect syntax.

You can press <Ctrl-Z>in any mode to immediately return to Privileged EXEC (enable) mode (8510#), instead of entering exit, which returns you to the previous mode.