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Tag: switch

  • How to create VLAN Interfaces for InterVLAN Routing in Cisco IOS

    VLAN Interfaces are required in network scenarios where you have different VLANs and need Inter-VLAN switching on Layer3 (Routing capable) switches. Every VLAN that needs to be routed should have a VLAN interface.

    Let’s say we have VLAN 10 which hosts the subnet 192.168.10.0 subnet, VLAN hosts 192.168.20.0 subnet and VLAN 30 hosts 192.168.30.0 subnet. For Inter-VLAN routing to work, we need to have a VLAN interface setup for each of these VLANs and configured with an IP address from the same subnet which will be the default Gateway for that subnet. Lets say, 192.168.10.254,192.168.20.254.192.168.30.254 are the IP addresses for VLAN Interfaces of VLAn 10,20,30 respectively.

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  • High CPU usage when SNMP is enabled in Cisco Routers

    Cisco Routers and Switches with L3 routing functions are seen to have problems with High CPU usage when SNMP is enabled. This can range anything from 15% to 40%. According to Cisco, these are low priority processes and other priority processes requiring CPU cycles are given priority over these processes and this level of CPU utilisation can be is normal. However, it is always better to be safe than sorry and get the CPU utilisation caused by SNMP to bare minimum so as to ensure the Routers function smoothly.

    The reason behind the High CPU usage can be caused by the Network Management Server (SNMP Server) like HP Openview querying for the Routing Tables and ARP tables to learn about other networks  or querying for certain MIBs which can be resource intensive.

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  • Logging Synchronous while working in Cisco Router/Switch Console

    Another beginner tip that can be useful!

    When you work on the Cisco Router or Catalyst Switch console, it would be annoying to have the console or terminal (telnet/ssh) logs to pop in between your commands. This can be even more irritating when it is busy switch or a router spitting messages continuously.

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  • Configure Access/trunk/Dynamic modes in Catalyst switches unconditionally

    In Cisco Catalyst switches, each switchport can be set to different VLAN Membership modes using the "switchport mode" command. This sets the port unconditionally.

    The different modes include

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  • VoIP Hopper – Opensource Security tool to test VoIP

    VoIP Hopper is a Unix/Linux based free opensource security tool that rapidly runs a VLAN Hop into the Voice VLAN on specific Ethernet switches. VoIP Hopper mimicks the behavior of an IP Phone, in both Cisco and Avaya IP Phone environments to hope into the Voice VLAN.  VoIP Hopper is both a VLAN Hop test tool and a tool to test VoIP infrastructure security. 

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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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