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Category Archives: Networking
Prevent IP Access by Routing to Null
The goal of a router is to send network traffic to its destination based on its routing table. Some times its necessary to prevent traffic form flowing through a router. This can typically be achieved with access control lists, but a cost. ACLs, particularly long and complicated ones, come with the cost of performance. When preventing access to an entire subnet it is possible to simply route traffic into a “black hole” where it will be discarded. This is achieved without using an ACL. Continue reading
Posted in Networking Tagged cisco, configuration, IOS, logging, networking, security Leave a comment
Introduction to Virtual Routing and Forwarding (VRFs)
If you have listened to anything IT in the past five plus years you have probably heard of and experienced the “virtualization” buzz word. Typically, it’s referencing host or server virtualization as this is the most common and well known. There are, however, other instances where virtualization of sorts can be used to break hardware into isolated network building blocks. Virtual Routing and Forwarding instances (VRFs) on Cisco routing devices are one such example. Continue reading
Moving a Subnet to a Different VLAN
There are a few different rare cases where you may need to move a subnet to a completely new or different VLAN. Making a layer 2 connection between two different networks with overlapping VLAN space or moving off of VLAN 1 for best practice reasons would be two examples. I will be focusing on the latter in this discussion but the steps will be applicable in other instances as well. To make this more practical lets keep the idea of very little to no downtime in mind. Continue reading
Traffic Rate Limiting with Monowall
Recently I was called to implement a system to limit the bandwidth used by our guest network. There was no firewall in place for this network aside from the device provided by the ISP. Needless to say, it was junk and supported none of the more advanced features we needed. I implemented a Monowall with a fairly typical setup and jumped into configuring the traffic shaper. In this article I will only be limiting traffic Continue reading
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