CISCO BGP protocol reduction techniques

">1 BGP BGP 1) is a kind of inter Cisco 3945 Cisco 3945 domain routing protocol (IDRP), the autonomous systemnumber is a 16 bit digital, which ranges from 1~6553564512~65535 AS number reserved for private: 2) between different autonomous system router running BGP, known as the external BGP(EBGP); between the same autonomous system router running BGP, known as BGP (IBGP); 3) EBGP usually are directly connected to each other, TTL value, the default value is 1; IBGP routers do not need to be directly connected neighbors, but the need to establish IGP,transmission is not required for IGP; 4) BGP routers only need to send the incremental update, BGP sends a live news; 5) was informed that the external network way: all BGP routing redistribution to all routers in theIGP; IBGP AS; 6) BGP maintenance: optimization; synchronization with IGP; the next hop up to; 7) routing will not run IBGP router from the neighbors learned to other routers; 8) BGP level segmentation, only the optimization of routing can be spread; 2 the BGP message type 1) to open the message (open): hold contains time and BGP routingID; 2) survival message (keeplive): three times in hold time; 3) update message (update): updates in the routing to the BGP optimal; 4) a notification message (notification):BGP routing error and BGP connection is management closure; 3 BGP Idle 1): the route table lookup, the router performs resource initialization, initiate a TCP connection, and listen to the remote BGP 2) Connect: find the routing table three handshake of TCP, TCP successfully connected toOpen sent state, if it fails, go to the idle to connect; 3) Open sent: open the information sending message; Open confirm: 4) received open message each other to neighbor relations, consultation; 5) Established: the final state. 4 BGP attribute 1) recognized attributes: recognized attributes are all manufacturers BGP implementation must be able to identify the attributes, recognized as mandatory attribute must appear on all BGP routing updates; recognized the freedom to decide property can not appear in the BGP update; 2) optional attribute: non recognized attribute called is optional, optional attributes can bedelivery or non delivery; 3) the BGP property defined: recognized as mandatory attribute; attribute recognized the freedom to decide; optional transfer property; optional non transitive properties; 4) AS path: a well-known property, to avoid the loop; 5) the next hop attribute: jump to BGP is AS, instead of the router, for another AS network, the next hop is the path to the network, a AS entrance IP address; 6) source: source is recognized as mandatory attribute, which defines the path informationsource, indicating the route is learned through what way. N IGP: internal routing in the initial AS; N EGP: routing through EGP was informed, in the form of BGP e, for example: weightdistribution; N incomplete: unknown source routing or by other methods such as: informed, redistribution or static routing; 7) local priority: the local AS to other AS multiple path first choose a path, the default local preference value is 100, the greater the value, the higher the priority; 8) community: a method for filtering into the station and the station route; community is optionalif the router does not recognize the transfer property, community, will leave it to the next routerto deal with; if the router to identify community, you must configure it, to spread the community,otherwise the community will be dropped; 9) MED (multi exit discriminators property): for external neighbor points out the preferred pathinto the AS. When the entrance with a plurality of time, AS can use MED to dynamically influence the other AS how to choose to enter the path, MED is the only attribute to a can influence the data into the AS, MED only in the EBGP transmission, the MED value is smaller,the more optimal path; Note: the effect of MED into the AS data stream, and the local priority effects of left AS data stream. 10) weight (Cisco only): is the router exports, while local priority attribute refers to the AS export,weight of attribute is in the router configuration, will not spread to any other router, only localdelivery, value is greater, the higher priority, the optimal path; the value range of 0~65535, the default weight path router advertisement the value is 32768; 5 routing decision process 1) preferred the highest weight router; (Cisco special, only for the current router) 2) select the local highest priority routing; (local priority for AS internal) 3) preferred local router Router: local network, need to configure the aggregated distribution or IGP; (the current router announcement the next hop routing for 0.0.0.0) 4) select AS shortest path routing; 5) source code path of minimal (IGPCisco 3925 price

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