We have seen earlier about the different types of peering. We have mandatory multilateral peering known as MMLP where each participant is forced to appear with every other participant as part of the membership this is no history of success and the practice is strongly discouraged. There may be a couple of instances worldwide where MMLP works out of the hundreds of exchange points in operation today. Multilateral peering known as MLP is where each participant peers with other participants usually via our art server we'll have a look at what a route server is soon bilateral peering is where participants at appearing with each other according to their own requirements and business relationships this is the most common situation at internet exchange parts today operators have three types of peering policies there is open peering for an ISP public States that they will appear with all parties who approach them for peering and this is commonly found at exchange points for ISPs participate via our art server selective peering is where an ISP Spearing policy depends on the nature of the operator who requests peering with them at exchange points operators will not peer with the right server but will only appear bilaterally and finally there's restrictive peering where an ISP decides who is peering partners are and is generally not approachable to creating peering opportunities the peering database documents ISPs peering policies and contact information and the URL is shown on the screen all operators of autonomous systems are encouraged to register in the peering database all operators who are considering peering or are appearing must be in the peering database to enhance the peering opportunity also participation in the peering fora is strongly encouraged there's a global peering forum which is used by the mid and larger ISPs but they're also regional peering fora for example in all the major continents Europe Middle East Asia Caribbean Latin America Africa and so on and in fact many countries now have their own peering fora taking place alongside or part of the various network operations groups let's have a look at some of the routing setup the operators need to consider at exchange points the ISP border routers at the exchange point must not be configured with a default route or carry the fool internet routing table carrying the default or the full table means that this router and the ISP network is open to abuse by non peer exchange point members the correct configuration is only to carry the rights offered to IXP peers on the IXP peering rata do note that some ISPs offer transit across ix5 breaks they do so at their own risk I would not recommend this at all it's easier and better to provide that transit service with a separate private network interconnect or P&I even in the same facility as the exchange point is located much better doing that than offering the transit across the exchange point fabric the ISP border routers of the exchange point should not be configured to carry the exchange point line within the internal BGP we have seen in the initial part of these presentations about the next hop self ibgp concept it's important that this is used and this means we don't need to carry the exchange point land around within our network keeping the exchange point line address block in the IGP however ensures that trace routes across the exchange point do not break and this may be useful for troubleshooting purposes also it's really important that the service provider does not generate the aggregates on their exchange point peering router if the connection from the backbone to the exchange point peering router goes down normal BGP failover will then be successful if they generate the aggregate on the peering router and the link from the peering router to the rest of the backbone goes down the peering router has no way of knowing that that link is broken and will carry on announcing the ISPs aggregate to the exchange point members while outbound traffic will proceed just fine from the member to the others via the members upstream transit provider the return traffic best path will be to the peering router that's just been disconnected from the backbone thereby cutting off the member from all the others across the exchange point.

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

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