On Junos, both OSPF and IS-IS have an overload setting. Although they perform a similar function, they achieve this through different methods. This leads to slightly different results when applying the overload setting. Note: Cisco does not have an overload command for OSPF. Instead, it has the ‘max-metric router-lsa’, which does a similar job. Why […]
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It can be difficult to troubleshoot the establishment of BGP sessions. Sometimes the issue is obvious, but other times it can be a vague and frustrating process. In this post, we will run through some of the tools available, the BGP Finite State Machine (FSM), and a general approach for troubleshooting BGP establishment. BGP Troubleshooting
Troubleshooting BGP Establishment Read More »
In the early stages of learning about BGP, we learn to set Local Preference on routes we learn from other networks to control how outbound traffic leaves our network. Then we learn to set AS Path prepending on routes we advertise to external networks to control how inbound traffic enters our network. We manipulate the
Why AS Path Prepending Doesn’t Always Work Read More »
What Is Proxy ARP? Proxy ARP is where one host responds to an ARP request on behalf of another device. Typically this is done by a router. The most common scenario is where a host on one network ARPs for a host on a remote network. The router detects this ARP and responds with its
What is the difference between a VLAN and a subnet? At first glance, they can feel very similar. This is especially true when the two terms are used somewhat interchangeably. When we connect a new device to the network and want to know how to address it, we might say any of the following: Each
VLANs versus Subnets – What’s The Difference Read More »
Is Static Routing More Secure Than Dynamic Routing? In static vs dynamic routing, I said that static routing is potentially more secure than dynamic routing. Let’s discuss this a bit more because there is little supporting information about why static routes are seen as more secure. And I’m not sure I agree that they are.
Are Static Routes More Secure Read More »
What Is A Static Route Static routes are routes that have been manually configured on a device by a network admin. These routes do not change until they are manually adjusted. Advantages Of Static Routing Disadvantages Of Static Routing Use Cases For Static Routing Static routing is normally used when: Let’s look at a few
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In this post, we will look at Cisco’s Administrative Distance (AD) and Juniper’s Route Preference. What Is Admin Distance And Route Preference Administrative distance on Cisco or route preference on Juniper is used to choose what route to use when the exact same route is learned via different routing protocols. It is a measure of
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What is the difference between a ping scan and an ARP scan? Why might these give different results? Both are used to identify what hosts are available or “alive” on a network but use different mechanisms for detecting hosts. Ping works by sending an ICMP Echo Request packet to the destination host and waiting for
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What is Gratuitous ARP? A Gratuitous ARP (or GARP) is where an ARP message is sent without a request being made. Why Use Gratuitous ARP? There are several reasons to use a Gratuitous ARP: Some common scenarios where a Gratuitous ARP might be sent include: Note that GARP is not used in duplicate address detection,