you may also have heard of something called a layer three exchange part these days it's a marketing concept used by transit ISPs some incumbent telcos call their domestic or international transit businesses exchanges they're exchanging packets so their argument is that they're an exchange point but they are not real internet exchange points are only layer two and layer two is the accepted international standard if we look at a layer three exchange design there are many things that cause problems for potential members first off there's one extra autonomous system hop between peers and that makes the path via the exchange point suboptimal or less preferred path between peers usually remains with the upstream transit provider unless the members are adept at doing the traffic engineering members cannot be with whom they please and basically you see the layer three exchange so-called implementing mandatory multilateral peering unless the exchange operator is very adept at handling BGP and BGP attributes the third party operator has to configure all the peering sessions configure the peering policy and manage the peering between the different members at the members requirements that's more complicated troubleshooting troubleshooting peering problems has to involve the exchange point operator as well there's no policy control BGP attributes share between members get dropped by the exchange point router common examples of those dropped would be the BGP communities and multi exit discriminators other issues include the fact that CD ends the content distribution networks won't join they often have requirements to peer directly with exchange point members and the redundancy issues as well layer three exchanges with dual sites appear as two separate transit providers between peers and then again it begs the question of how the traffic engineering could work and the final issue is that the layer three exchange part operator requires strong bgp skills so the general advisors do not even consider layer three exchange parts they're not internet exchange parts there are service providers transit network masquerading as an Internet the industry standard doesn't mentioned in the start of this clip is layer two and today that is really just an Ethernet switch

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

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