It is important to understand that any TCP packet that is routed over a network requires bi-directional support. This means that even though I may have a route on my router to your network, if you don’t have a route back to me, the transmission of packets will fail. TCP uses acknowledgments to confirm the [...]

OSPF (Open Shortest Path First) is an industry open standard supported by almost every router on the planet.   OSPF is a classless routing protocol so subnetmask values are sent in the update and it supports CIDR. OSPF does not send periodic updates and is designed to only send updates when something has changed or [...]

EIGRP (Enhanced Inter-Gateway Routing Protocol) is one of the fastest most reliable routing protocols available today, but it’s drawback is that it’s a Cisco proprietary protocol which means you either need a network that is running 100% Cisco, or have devices that support EIGRP in your network.   EIGRP is a classless routing protocol so [...]

A routing protocol is a method that routers use to share information with each other about networks they are connected to. We have seen in previous posts on this website (Creating a Static Route and Default Gateway of Last Resort) how we make routes ourselves and how to teach a router how to send packets [...]

Before we can start to explain how routing protocols work, we need an understanding of wildcard masks.   The concept of wildcard mask is one that many people struggle with at first, but with a little time and practice it’s becomes second nature. Converting a full class subnet mask into a wildcard mask quite straight [...]

The Cisco administrative distance is a value assigned to all routing protocols to define how trustworthy the information is.   If a Cisco router has multiple routes in its routing table for the same network, it looks to see which route has the lowest cost/metric value. The problem with using cost values is that different [...]

In yesterday’s post ‘Static Routing’ we saw that we needed to create a static route to allow the Cisco router “AOIP.ORG” to ping “R2″. The static route that we created was ‘ip route 10.0.1.0 255.255.255.0 192.168.1.1′ and ping was successful to the IP address 10.0.1.2 (R2′s Serial interface). The problem with that configuration was that [...]

A router by default only knows about networks that are directly connected to it. If a router is not directly connected to the final destination subnet, then the router needs to learn, or be told how to get to that destination.   Learning routes can take place through the use of routing protocols, however in [...]

In order to set up an IP address on an interface, we need to be in the interface level of the command line. This is a level within the global configuration level. From global configuration mode, we can enter the ‘interface serial 1/0’ command. If you are unsure of what interfaces are on the router, [...]

Every Cisco device has 2 sets of configurations. On routers and switches these configurations are called ‘running-config’ and ‘startup-config’ When you make any changed on a router or switch, the change applies to the running-configuration and will affect the router or switch with immediate effect. However, if the device is reloaded for whatever reason, all [...]