We've just finished discussing route collectors so let's have a look at a route server. It has got all the features of a route collector but also announces routes to participating exchange point members according to the routing policy definitions and is implemented using the same specification as for a route collector. So the typical features of a route server are these: it helps scale route distribution for exchange points, forwarding of packets is unaffected, traffic does not go through a route server because it makes use of a BGP functionality known as third party next-hop, which we covered in the BGP attribute introduction, it simplifies the routing processes on ISP routers, participation is optional, is provided by the exchange point as a service to members, it is never mandatory if a traditional router is used and that's getting rarer and rarer these days it will result in insertion of the route server autonomous system number in the air span so we generally want to avoid this the route server is there to scale route distribution not look like an alternative path through the exchange point route service optionally could use policy which is registered and internet routing registry to facilitate the peering configuration between exchange point members the diagram shows the typical n-squared peering mesh I remember we add at the exchange point means that member will have to set up peering with every other member if appropriate and for large exchange points maintaining this large pyramid becomes cumbersome and is often too hard a better solution as the diagram shows is to implement the route service the two in the diagram and the ISP routers will appear with the two right servers there this means they only need two ebgp session rather than ebgp with every other member at the exchange point the route server routing information flow is shown in this diagram and the route servers there to scale BGP the traffic flow follows the solid arrows the routing information flow follows the dotted arrows a common misconception is somehow that the route server is going to carry all the exchange point traffic as well it doesn't all the carries is the routing information shared between the various exchange point members traffic remains running directly between the connected routers over the exchange point Ethernet LAN it does not go anywhere near the right server so the advantages of a route server are that they help scaling the larger exchange points by scaling the ebgp mesh and scaling prefix distribution it separates the routing and the forwarding and it simplifies the BGP configuration management on is paratus meaning the ISPs don't need to maintain a large number of ebgp peers as they only need to peer with the route server of course there are a few disadvantages which should be considered as well ISPs could lose direct policy control if route servers the only peer the ISPs have no control over who the prefixes are distributed to and this is fine if the ISP has an open peering policy with selective or restricted peering policy is not clear of a route server would be useful for the ISP member the eye speed becomes completely dependent on a third party the configuration troubleshooting and reliability of the right server if there's a problem with the route server the ISP will lose the peering and connectivity with the peers it has learned through the right server and there's the possible insertion of the right servers a s number into the routing path and this happens if using a router rather than a dedicated route server bgp implementation and so if this happens traffic engineering and multihoming needs more care so route servers are provided as an optional service these days at exchange points and indeed most exchange points now offer a route server as a service to members even you exchange points with just a few members ISPs peer directly with significant peers and with the right server for the rest is peas with an open peering policy usually prefer to appear with a right server the implementations we see today are shown on the slide the most common and the standard which works best is burped at the URL shown on the screen gule BGP is also being used by some exchangers now and quagga a long-term favorite is also used at some exchange parts but note this is quagga that has been developed and improved by links to help with scaling of that exchange point in the UK there's also a new fork of quagga where the software is being worked on to improve it to help it scale better than the original implementation routers can be used and any router will work just fine but with the caveat of the right server autonomous system appearing in the air spaz indeed Cisco IOS 15.2 onwards and iOS X e 3.7 onwards has a route server client configuration available but very few exchange points actually use a physical router for this function given berried is pretty much the world standard for the route server implementation so some things to think about for new exchange points. Would a route server benefit your exchange point? It's certainly helpful for when BGP knowledge is limited but, of course, is not an excuse not to learn BGP and it does help having to avoid maintaining a large number of eBGP peers.
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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