Switch administration

1.1.a i Managing MAC address table

CAM table

Content Addressable Memory

General information on “CAM Table”:

• Also known as MAC Address Table
• MAC address-to-port mappings
• Used for Layer 2 forwarding decisions
• Table is built by recording the source MAC address, inbound port and VLAN but can also be filled manually
• If destination MAC address is known = direct forwarding to specific port
• If destination MAC address is unknown = flooding out of all ports within the VLAN (except the receiving one)
• Space in CAM table is limited so that MAC addresses which haven’t been heard of within a given time age out (stale entries, can be disabled)
• The CAM table logic provides two results: 0 (true), 1 (false)

“CAM Table” timers default values:

• Aging time: 300 seconds (5 minutes)

“CAM Table” CLI configuration commands:

## Configuring a static MAC table entry
Switch(config)# mac address-table static <mac-addr> vlan <vlan-id> interface <if>

## Modifying the MAC table age-out timer
Switch(config)# mac address-table aging-time <aging-time>

“CAM Table” CLI show commands:

## Showing all current MAC table entries
Switch# show mac address-table

## Showing the current MAC table count and remaining available address space
Switch# show mac address-table count

TCAM Table

Ternary Content Addressable Memory

General information on “TCAM Table”:

• Found in multilayer switches and routers
• Contains all the information from ACLs, QoS and other for upper-layer processing
• Switches can have multiple TCAM tables to boost performance
• Multiple TCAM tables allow multiple checks in parallel
• Each TCAM table consists of three field: value, mask, result (VMR)
• Value and mask field are 134 bit in size
• For complex ACLs (eg. With port range, …) a LOU (Logical Operation Unit) register is created within the table The CAM table logic provides three results: 0 (true), 1 (false), “don’t care”

“TCAM table” CLI show commands:

## Showing the current TCAM table utilization
Switch# show platform tcam utilization

1.1.a ii Errdisable recovery

General information on “Errdisable recovery”:

• By default, an errdisabled port must be manually reset
• Automatic errdisable recovery is possible
• It is configured on a global basis
• Can be enabled for all or only specific causes
• Errdisable interval can be fine-tuned based on environment needs

“Errdisable recovery” default timers:

• Interval: 300 seconds (5 minutes)

“Errdisable recovery” CLI configuration commands:

## Configuring the disabled/enabled errdisable detection causes
Switch(config)# errdisable detect cause [all | <specific>]

## Configuring the disabled/enabled errdisable recovery causes
Switch(config)# errdisable recovery cause [all | <specific>]

## Modifying the errdisable recovery interval
Switch(config)# errdisable recovery interval <seconds>

“Errdisable recovery” CLI show commands:

## Showing the disabled/enabled errdisable detection causes
Switch# show errdisable detect

## Showing the disabled/enabled errdisable recovery causes and interval
Switch# show errdisable recovery

1.1.a iii L2 MTU

Layer 2 Maximum Transmission Unit

General information on “L2 MTU”:

• Defines the Layer 2 MTU size for all interfaces on a switch
• This is the maximum size of an Ethernet Frame (excluding header and checksum) the switch can forward
• The default value is 1500 bytes

“L2 MTU” CLI configuration commands:

## Configuring the L2 MTU
Switch(config)# system mtu <size>

“L2 MTU” CLI show commands:

## Showing the currently configured L2 MTU
Switch# show system mtu