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Tag: Cisco

  • How to configure Cisco Router as Authoritative DNS Server

    While we saw here how to setup a Cisco Router as a Caching/Forwarding DNS Server. We can now look at how to make your Cisco Router as an Authoritative DNS server. When configured as an authoritative name server for its own local host table, the router listens on port 53 for DNS queries and then answers DNS queries using the permanent and cached entries in its own host table.

    Careful consideration has to be given as this can consume considerable amount of resources like CPU cycles on the Cisco Router. If you are a small network and realise your Cisco ROuter is under utilised then there is a good business case to turn your router into a DNS server.

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  • Enable/Disable subnet Zero in Cisco Routers (IOS 12.x)

    When you subnet a network into multiple subnets, the first subnet created is called the Subnet Zero whose network address will be exactly be the same as the actual Network Address.

    This can create confusions and importantly in legacy hardware can cause routing issues. However, newer network routers and Cisco Routers running Cisco IOS 12.x can handle these Subnet-Zero without any problem. Cisco IOS 12.x by default enables subnet-zero.

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  • Configure Cisco Router as Caching/Forwarding DNS Server

    A Cisco Router running Cisco IOS can function as a Caching or Forwarding DNS Server which answers to DNS queries from clients either from its host table or cache or forward it to a DNS server which can respond to the query.

    This feature can come in handy in small network environments where the router can act as a Caching DNS server forwarding queries to the ISPs DNS servers or infact any external DNS servers. Also, makes sense using on under utilized DNS servers.

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  • Configure Multiple IP Address on a Cisco Router Interface

    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.

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  • How to Configure Multiple Interfaces in Cisco IOS

    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.

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  • How to setup IP Policy based routing in Cisco Router(IOS)

    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).

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  • How to configure Redundant Supervisor Engine module in Cisco IOS

    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.

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