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Tag: Cisco

  • How to add/modify Standard Access Control List (ACL) Cisco router

    ACLs in Cisco IOS can be used to control traffic flow and to use it as a simple list to define another function like NATing or Route-Maps. Standard Access List (ACL) in Cisco IOS are the simplest and oldest type of ACLs. Standard ACLs simply compare the Source IP Address on the packet against the IP Address defined on the ACL and decides whether to permit or deny the traffic as per the definition in the ACL.

    When used to control traffic, it is recommended that the ACLs in general are applied to the interface closest to the segment where the traffic originates.

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  • How to set Summer Time (Daylight Savings Time) in Cisco IOS

    The Day Light savings time kicked in today in the UK today and it is this part of the year (and when the GMT kicks back in) we do a sanity check on all the Network Devices, Appliances and Servers for time.

    It is important to set the time appropriately on the devices as an incorrect time on the devices can cause authentication issues and ofcourse incorrect time stampls on the logs.

    You can enable the Day Light Savings time in Cisco IOS. This just takes a couple of commands from the Global Configuration mode.

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  • How to configure HSRP in Cisco IOS Routers

    HSRP stands for Hot Standy Routing Protocol which provides Automatic Router backup when an active router in the group fails. HSRP allows building resiliency in the network gateways wherein should an Active Router fail in a HSRP group, the standby router assumes the role of the active router and continue routing packets.

    HSRP works by sending multicast "Hello" messages (default: every 3 secs). If the Standby router do not receive any Hello packets from the active router for a preset time (default 10secs) then it assumes the active router is down and becomes the active router. Also, if we are tracking an interface and if the tracked interface is down, the Active Router reduces its priority so a Standby Router can assume to role of Primary Router.

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  • How to set Passwords in Cisco IOS Routers and Switches

    One of the basic configurations when setting up a Cisco Router or a Cisco Switch is setting the passwords. This includes, setting the passwords for the Console, Telnet/SSH and the Enable (Enable Secret)

    The following procedure will help starters set up passwords in Cisco Routers and Switches running Cisco IOS.

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  • How to setup 802.1q Trunk Port in Cisco Switches (IOS)

    Trunk Ports are switchports on Cisco switches that interconnect switches. The trunk port carries traffic for all the VLans across the switches it interconnects. switchport can be enabled and configured as trunks without much trouble.

    The following procedure helps setting a switchport into a Trunk port with 802.1q encapsulation.

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  • How to prevent Routing updates on interfaces of Cisco Routers

    When we configure a routing protocol on Cisco IOS Routers, it is important to consider preventing Routing updates sent on interfaces that are not required to (say a LAN where there is no other router in the segment to receive any updates). This ensure we are not passing updates that could cause network issues. Needless to say, the network becomes less chatty and can make life more easy when sniffing or spanning for network troubleshooting.

    In Cisco IOS we can globally or selectively prevent interfaces on which we do not want routing updates to be sent. Ideally, it would be better that we do this globally and then selectively allow interfaces that can send routing updates.

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