Cisco IOS supports multiple IP Addresses on an interface. There will be one Primary IP Address on the interaface and multiple Secondary IP Addresses on the interface. There is no limit on the number of IP Addresses that can be configure on an interface. Configurng multiple IP Addresses on your cisco routers can sometime help where you have multiple subnets having one physical router interface.
The IP Addresses can be from different subnets and from different networks.
In Cisco IOS, "interface range" command can help you configure multiple interfaces in one single command. This can be a range of switch ports on a module or multiple ports on multiple module be it FastEthernet or GigabitEthernet or vlans on a Cisco Switch or a Router.
Sometimes, simple tasks like enabling a bunch of Administratively shutdown ports, assigning a range of switchports to a particular VLAN can become boring and tedious. This is where the "interface range" can help where we can specify a comma seperated list of range of ports or vlans in the interface configuration mode and any command issued from there will apply to all switchports.
Cisco routers running Cisco IOS supports pased based IP Routing which can route packets based on a set IP Policy exiting an Interface.
Policy based routing in Cisco ROuters can be performed by using "route-map" and then applying as a policy to the interface of the IP Packets.
The route-map has a list of "match" and "set" commands where match defines the criteria under which the policy routing is performed (say, match a destination IP or a standard or Extended ACL) and set defines the actions to perform when match criteris met (say, set next hop).
Cisco Catalyst Switches like Catalyst 6500 series and Catalyst 4500-R series and highend routers lsupport Redundant Supervisor modules to be installed. The Redudndant Supervisor Modules startup and run as a standby device and takes over when the active module fails. The Active Supervisor Engine syncs time and config onto the redundant supervisor engine every 1 sec and when running-config is copied to the Start-up config. The failover mode Stateful switchOver (SSO) we use here allows failover in 1 second or more.
Check your Catalyst switch / Routers and the Supervisor Engine documentation for the supported modes of redundancy.
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.
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.
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.