ChristianC123

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  1. Overview of Port Security You can use the port security feature to restrict input to an interface by limiting and identifying MAC addresses of the workstations that are allowed to access the port. When you assign secure MAC addresses to a secure port, the port does not forward packets with source addresses outside the group of defined addresses. If you limit the number of secure MAC addresses to one and assign a single secure MAC address, the workstation attached to that port is assured the full bandwidth of the port. If a port is configured as a secure port and the maximum number of secure MAC addresses is reached, when the MAC address of a workstation attempting to access the port is different from any of the identified secure MAC addresses, a security violation occurs. After you have set the maximum number of secure MAC addresses on a port, the secure addresses are included in an address table in one of these ways: •You can configure all secure MAC addresses by using the switchport port-security mac-addressmac_address interface configuration command. •You can allow the port to dynamically configure secure MAC addresses with the MAC addresses of connected devices. •You can configure a number of addresses and allow the rest to be dynamically configured. Note If the port shuts down, all dynamically learned addresses are removed. •You can configure MAC addresses to be sticky. These can be dynamically learned or manually configured, stored in the address table, and added to the running configuration. If these addresses are saved in the configuration file, the interface does not need to dynamically relearn them when the switch restarts. Although sticky secure addresses can be manually configured, it is not recommended. You can configure an interface to convert the dynamic MAC addresses to sticky secure MAC addresses and to add them to the running configuration by enabling sticky learning. To enable sticky learning, enter the switchport port-security mac-address sticky command. When you enter this command, the interface converts all the dynamic secure MAC addresses, including those that were dynamically learned before sticky learning was enabled, to sticky secure MAC addresses. The sticky secure MAC addresses do not automatically become part of the configuration file, which is the startup configuration used each time the switch restarts. If you save the sticky secure MAC addresses in the configuration file, when the switch restarts, the interface does not need to relearn these addresses. If you do not save the configuration, they are lost. If sticky learning is disabled, the sticky secure MAC addresses are converted to dynamic secure addresses and are removed from the running configuration. After the maximum number of secure MAC addresses is configured, they are stored in an address table. To ensure that an attached device has the full bandwidth of the port, configure the MAC address of the attached device and set the maximum number of addresses to one, which is the default. Note When a Catalyst 4500 series switch port is configured to support voice as well as port security, the maximum number of allowable MAC addresses on this port should be changed to three. A security violation occurs if the maximum number of secure MAC addresses has been added to the address table and a workstation whose MAC address is not in the address table attempts to access the interface. You can configure the interface for one of these violation modes, based on the action to be taken if a violation occurs: •Restrict—A port security violation restricts data, causes the SecurityViolation counter to increment, and causes an SNMP Notification to be generated. The rate at which SNMP traps are generated can be controlled by the snmp-server enable traps port-security trap-rate command. The default value ("0") causes an SNMP trap to be generated for every security violation. •Shutdown—A port security violation causes the interface to shut down immediately. When a secure port is in the error-disabled state, you can bring it out of this state by entering the errdisable recovery cause psecure-violation global configuration command or you can manually reenable it by entering the shutdown and no shut down interface configuration commands. This is the default mode. You can also customize the time to recover from the specified error disable cause (default is 300 seconds) by entering the errdisable recovery interval interval command. Default Port Security Configuration Table 32-1 shows the default port security configuration for an interface. Table 32-1 Default Port Security Configuration Feature Default Setting Port security Disabled on a port Maximum number of secure MAC addresses 1 Violation mode Shutdown. The port shuts down when the maximum number of secure MAC addresses is exceeded, and an SNMP trap notification is sent. Aging Disabled Aging type Absolute Static Aging Disabled Sticky Disabled Port Security Guidelines and Restrictions Follow these guidelines when configuring port security: •A secure port cannot be a trunk port. •A secure port cannot be a destination port for Switch Port Analyzer (SPAN). •A secure port cannot belong to an EtherChannel port-channel interface. •A secure port and static MAC address configuration are mutually exclusive. Configuring Port Security These sections describe how to configure port security: •Configuring Port Security on an Interface •Configuring Port Security Aging Configuring Port Security on an Interface To restrict traffic through a port by limiting and identifying MAC addresses of the stations allowed to access the port, perform this task: Command Purpose Step 1 Switch(config)# interface interface_id Enters interface configuration mode and enters the physical interface to configure, for example gigabitethernet 3/1. Step 2 Switch(config-if)# switchport mode access Sets the interface mode as access; an interface in the default mode (dynamic desirable) cannot be configured as a secure port. Step 3 Switch(config-if)# switchport port-security Enables port security on the interface. Step 4 Switch(config-if)# switchport port-security maximum value (Optional) Sets the maximum number of secure MAC addresses for the interface. The range is 1 to 3072; the default is 1. Step 5 Switch(config-if)# switchport port-security violation {restrict | shutdown} (Optional) Sets the violation mode, the action to be taken when a security violation is detected, as one of these: •restrict—A port security violation restricts data and causes the SecurityViolation counter to increment and send an SNMP trap notification. •shutdown—The interface is error-disabled when a security violation occurs. Note When a secure port is in the error-disabled state, you can bring it out of this state by entering the errdisable recovery cause psecure-violation global configuration command or you can manually reenable it by entering the shutdown and no shut downinterface configuration commands. Step 6 Switch(config-if)# switchport port-security limit rate invalid-source-mac Sets the rate limit for bad packets. Step 7 Switch(config-if)# switchport port-security mac-address mac_address (Optional) Enters a secure MAC address for the interface. You can use this command to enter the maximum number of secure MAC addresses. If you configure fewer secure MAC addresses than the maximum, the remaining MAC addresses are dynamically learned. Step 8 Switch(config-if)# switchport port-security mac-address sticky (Optional) Enable sticky learning on the interface. Step 9 Switch(config-if)# end Returns to privileged EXEC mode. Step 10 Switch# show port-security address interface interface_id Switch# show port-security address Verifies your entries. •To return the interface to the default condition as not a secure port, use the no switchport port-security interface configuration command. •To return the interface to the default number of secure MAC addresses, use the no switchport port-security maximum value. •To delete a MAC address from the address table, use the no switchport port-security mac-addressmac_address command. •To return the violation mode to the default condition (shutdown mode), use the no switchport port-security violation {restrict | shutdown} command. •To disable sticky learning on an interface, use the no switchport port-security mac-address stickycommand. The interface converts the sticky secure MAC addresses to dynamic secure addresses. •To delete a sticky secure MAC addresses from the address table, use the no switchport port-security sticky mac-address mac_address command. To delete all the sticky addresses on an interface or a VLAN, use the no switchport port-security sticky interface interface-id command. •To clear dynamically learned port security MAC in the CAM table, use the clear port-security dynamic command. The address keyword enables you to clear a secure MAC addresses. The interface keyword enables you to clear all secure addresses on an interface. This example shows how to enable port security on Fast Ethernet port 12 and how to set the maximum number of secure addresses to 5. The violation mode is the default, and no secure MAC addresses are configured. Switch# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)# interface fastethernet 3/12 Switch(config-if)# switchport mode access Switch(config-if)# switchport port-security Switch(config-if)# switchport port-security maximum 5 Switch(config-if)# switchport port-security mac-address sticky Switch(config-if)# end Switch# show port-security interface fastethernet 3/12 Port Security :Enabled Port Status :Secure-up Violation Mode :Shutdown Aging Time :0 Aging Type :Absolute SecureStatic Address Aging :Enabled Maximum MAC Addresses :5 Total MAC Addresses :0 Configured MAC Addresses :0 Sticky MAC Addresses :11 Last Source Address :0000.0000.0401 Security Violation Count :0 This example shows how to configure a secure MAC address on Fast Ethernet port 5/1 and verify the configuration: Switch# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)# interface fastethernet 5/1 Switch(config-if)# switchport mode access Switch(config-if)# switchport port-security Switch(config-if)# switchport port-security maximum 10 Switch(config-if)# switchport port-security mac-address 0000.0000.0003 (Static secure MAC) Switch(config-if)# switchport port-security mac-address sticky Switch(config-if)# switchport port-security mac-address sticky 0000.0000.0001 (Sticky static MAC) Switch(config-if)# switchport port-security mac-address sticky 0000.0000.0002 Switch(config-if)# end Switch#show port address Secure Mac Address Table ------------------------------------------------------------------------ Vlan Mac Address Type Ports Remaining Age (mins) ---- ----------- ---- ----- ------------- 1 0000.0000.0001 SecureSticky Fa5/1 - 1 0000.0000.0002 SecureSticky Fa5/1 - 1 0000.0000.0003 SecureConfigured Fa5/1 - ------------------------------------------------------------------------ Total Addresses in System (excluding one mac per port) : 2 Max Addresses limit in System (excluding one mac per port) : 1024 Configuring Port Security Aging You can use port security aging to set the aging time and aging type for all secure addresses on a port. Use this feature to remove and add PCs on a secure port without manually deleting the existing secure MAC addresses while still limiting the number of secure addresses on a port. To configure port security aging, perform this task: Command Purpose Step 1 Switch(config)# interface interface_id Enters interface configuration mode for the port on which you want to enable port security aging. Step 2 Switch(config-if)# switchport port-security [ aging {static | time aging_time | type {absolute | inactivity} ] Sets the aging time for the secure port. The static keyword enables aging for statically configured secure addresses on this port. The time aging_time keyword specifies the aging time for this port. Valid range for aging_time is from 0 to 1440 minutes. If the time is equal to 0, aging is disabled for this port. The type keyword sets the aging type as absolute or inactive. For absolute aging, all the secure addresses on this port ago out exactly after the time (minutes) specified and are removed from the secure address list. For inactive aging, the secure addresses on this port ago out only if there is no data traffic from the secure source address for the specified time period. Step 3 Switch(config-if)# end Returns to privileged EXEC mode. Step 4 Switch# show port security [interface interface_id] [address] Verifies your entries. To disable port security aging for all secure addresses on a port, use the no switchport port-securityaging time interface configuration command. This example shows how to set the aging time as 2 hours for the secure addresses on the Fast Ethernet interface 5/1: Switch(config)# interface fastethernet 5/1 Switch(config-if)# switchport port-security aging time 120 This example shows how to set the aging time as 2 minutes: Switch(config-if)# switchport port-security aging time 2 You can verify the previous commands by entering the show port-security interface interface_id command. Displaying Port Security Settings Use the show port-security command to display port-security settings for an interface or for the switch. Regards Christian Network Admin
  2. Class A Subnets In Class A, only the first octet is used as Network identifier and rest of three octets are used to be assigned to Hosts (i.e. 16777214 Hosts per Network). To make more subnet in Class A, bits from Host part are borrowed and the subnet mask is changed accordingly. For example, if one MSB (Most Significant Bit) is borrowed from host bits of second octet and added to Network address, it creates two Subnets (21=2) with (223-2) 8388606 Hosts per Subnet. The Subnet mask is changed accordingly to reflect subnetting. Given below is a list of all possible combination of Class A subnets: In case of subnetting too, the very first and last IP address of every subnet is used for Subnet Number and Subnet Broadcast IP address respectively. Because these two IP addresses cannot be assigned to hosts, sub-netting cannot be implemented by using more than 30 bits as Network Bits, which provides less than two hosts per subnet. Class B Subnets By default, using Classful Networking, 14 bits are used as Network bits providing (214) 16384 Networks and (216-2) 65534 Hosts. Class B IP Addresses can be subnetted the same way as Class A addresses, by borrowing bits from Host bits. Below is given all possible combination of Class B subnetting: Class C Subnets Class C IP addresses are normally assigned to a very small size network because it can only have 254 hosts in a network. Given below is a list of all possible combination of subnetted Class B IP address: Regards Christian Network Admin