When two or more sources are giving you information about a certain prefix you need to choose which information you are going to use. For example OSPF might tell you to go “left” if you want to reach network X, EIGRP might tell you that you need to go “right”. Who do you trust? OSPF or EIGRP? You can’t put both in the routing table for network X.
Perhaps you have heard about the term “wirespeed” before. It’s something the marketing department likes to use when it comes to selling networking equipment. It means that packets can be forwarded without any noticeable delay. Oh btw, for the remaining of this lesson the words “multilayer switch” and “router” are the same thing. Everything that I explain about the multilayer switches from now on also applies to routers.Let’s take a look at the difference between layer 2 and multilayer switches from the switch’s perspective:
Policy-based routing can be used to change the next hop IP address for traffic matching certain criteria. This can be useful to overrule your routing table for certain traffic types. I will show you how to configure policy based routing.
IP SLA (Service-Level Agreement) is a great feature on Cisco IOS devices that can be used to “measure” network performance.
This can be something simple like a ping where we check the round-trip time or something more advanced like a VoIP RTP packet where we check the delay, jitter and calculate a MOS score that gives you an indication what the voice quality will be like.
IP SLA is a great tool on Cisco routers that allows us to generate traffic which can be used to check delay/latency, jitter but can also be combined with object tracking. This allows us to check the reachability of a certain IP address (by pinging) or a certain service by connecting to it (using TCP). If the IP address/service is unreachable we can apply a certain action. A simple example to demonstrate IP SLA is when you have a single router that is connected to two ISPs:
In previous blogs we discussed how wecan use PBR (Policy Based Routing) to overrule the routing table for certain types of traffic. we also discussed in another blog how IP SLA can be used to measure your network performance.