Category Archives: Vlan

Filtering traffic with vlan access list

Topology Lab setup Linux 2 belongs to vlan 10. Linux 3 and 4 belong to vlan 20. Router is the dhcp server for vlan 10 and 20. A default route goes from Router to the internet where the web application … Continue reading

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VLAN Trunking Protocol

This is a Cisco proprietary protocol that is designed to ease Vlan database management, it has nothing to do with trunking. The concept is that a switch with a VTP server mode will propagate VLAN database down to all switches … Continue reading

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Catalyst Switch: Turn off trunking negotiation

To turn off dynamic trunking protocol (DTP) and use dot1q standard. It is recommended to turn off trunking protocol and put vtp to transparent mode, this is because a newly introduced Catalyst switch may form undesired switch topology and if … Continue reading

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Catalyst Switch: No trunks is formed

I have connected two Cisco Catalyst 3560 switches together by a pair of fibre cables. No trunk was formed. The default interface configuration for Catalyst 3560 is dynamic auto, in Catalyst 3550 the default was dynamic desirable. Dynamic desirable is … Continue reading

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Security: Private vlan example

Private vlan 1. Before you start make sure the vtp mode is set to transparent. 2. The difference between private vlan and protected port is protected port is localized within the switch itself, but private vlan can propagate among switches. … Continue reading

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