What is the difference between explicit versus default routing? Default routing points all destinations to another device this is very simple and cheap as it requires very low cpu, memory and bandwidth. It also has no overheads and has very low granularity. Explicit routing points to every known destination this is also known as the default free zone this is very complex and expensive as it requires a lot of cpu memory and bandwidth it also has very high overheads and high granularity a compromise between default and explicit routing is the hybrid routing this contains the default routing plus some known destinations this minimizes overheads and also provides useful granularity knowledge of filtering is required for implementing hybrid routing we're now going to talk about egress traffic when we talk about egress traffic we mean how do packets leave your network egress traffic depends on route availability this is what others send around acceptance this is what you accept from others policy and tuning this is what you do with the route from others as well as your peering and transit agreements when we talk about inquest traffic we mean how packets enter your network ingress traffic depends on what information you send and to whom it's also based on your addressing and your ass and it's also based on others policy this is what they accept from you and what they do with it when we talk about autonomous systems we mean a collection of networks with the same routing policy and single routing protocol asses are usually under single ownership trust and administrative control we're going to talk about a few more definitions when you hear the term neighbors this simply means asses which directly exchange routing information and it can also mean routers which exchange routing information when we talk about announcements we mean sending routing information to a neighbor accepting a route means receiving and using routing information sent by a neighbor originating a route implies inserting routing information into external announcements usually as a result of igp and when we talk about pairs we usually refer to routers in neighboring ass or within one as which exchange routing and policy information we're now going to talk about routing versus packet flow as you can see from the screen you have two different ass this is as1 and as2 for networks in as1 and as2 to communicate as1 must first announce to as2 as2 must then accept from as1 for packet to flow from as1 to as2 for packets to fall from as2 to as1 as2 must announce to as1 as1 was 10 except from as2 for packets to flow from as2 to as1 Routing and traffic flow. Traffic flow is usuallyin the opposite direction of the flow of routing information. Please remember that filteringoutgoing routing information inhibits traffic flow inbound whereas filtering inbound routing information inhibits traffic flow outbound.

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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