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GT ECE 4110 - Border Gateway Protocol

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Slide 1Path Vector RoutingSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 171Border Gateway Protocol (BGP)Between Autonomous Systems: uses path vector routing.This routing protocol uses TCP and port #179. Messages are encapsulated in TCP.For between autonomous systems:•Distance Vector not good to use because do not always want to use smallest hop count•Link state not good - Internet is too large for this approach. Data base too large, shortest path algorithm calculations do not scale wellSource: TCP/IP Protocol Suite, by Fourouzan2Path Vector RoutingRouting table entries consist of destination network, next router, autonomous system path to reach destinationExample path vector routing tableDestination Network Next Router PathN01 R07 AS5, AS19, AS21N02 R10 AS14, AS8, AS7N03 R2 AS4, AS9, AS6N04 R3 AS1, AS2Autonomous Boundary Routers advertise to their neighbors how to get to networks inside their own autonomous systems34BGP Types of MessagesTypes are: OPEN, UPDATE, KEEPALIVE,NOTIFICATIONPacket Formats:All BGP packets have same common header:Marker 16 bytesType 8 bitsLength 16 bitsMarker - Fields for authenticationLength - Length of entire BGP message including common header shown hereType - Identifies which of the four message types this is.5Open MessageBGP Identifier 32 bitsVersion 8 bitsMy autonomous system 16 bits Hold Time 16 bitsOption LengthVariable Length OptionType in common header = 1Version - Version is 4 at present in the internetMy Autonomous System - Autonomous System NumberHold Time - Max number of seconds before must receive update or a keep alive message or we consider other router deadBGP ID - Four byte IP of router sending OptionsUse this message type to open a connection (TCP connection used) with neighbor6Update MessageUsed to remove destinations that were advertised previously, announce new route. BGP is allowed to remove several destinations but only to add one new in each update message.Path Attribute Length 16 bitsUnfeasible Routes Length 8 bitsWithdrawn Routes is of variable lengthVariable Length Path AttributesVariable Length Network Layer Reachability InfoUnfeasible Routes Length - Length of next fieldWithdrawn Routes - List of routes to removePath Attributes Length - Length of next fieldPath Attributes - Info like ORIGIN: RIP, OSPF, etc generated route info;AS_PATH: List of autonomous systems through which we go to get to destination;Next Hop: Router where we should send packetNetwork Layer Reachability Info - Network IP and number of bits in mask7Keep Alive MessageThe Routers exchange Keep Alive messages. (2 Minutes common)The message itself is just a common BGP Header Message with Type = 3Notification MessageSent when error is detected or router wants to close the connection.Message consists of error codes, error subcase, and error data.Type = 4 Error Code 8 bitsVariable Length Error dataError Subcode 8 bits8spawn telnet route-server.ip.att.netTrying 12.0.1.28...Connected to route-server.cbbtier3.att.net.Escape character is '^]'.CCC############## route-server.ip.att.net ######################## AT&T IP Services Route Monitor ########### This router maintains peerings with customer-facing routersthroughout the AT&T IP Services Backbone: 12.123.21.243 Atlanta, GA 12.123.133.124 Austin, TX 12.123.41.250 Cambridge, MA 12.123.5.240 Chicago,IL 12.123.17.244 Dallas, TX 12.123.139.124 Detroit, MI 12.123.37.250 Denver, CO 12.123.134.124 Houston, TX 12.123.29.249 Los Angeles, CA 12.123.1.236 New York, NY 12.123.33.249 Orlando,FL 12.123.137.124 Philadelphia, PA 12.123.142.124 Phoenix, AZ 12.123.145.124 San Diego, CA 12.123.13.241 San Francisco, CA 12.123.25.245 St. Louis, MO 12.123.45.252 Seattle, WA 12.123.9.241 Washington, DC This router has the global routing table view from each of the aboverouters, providing a glimpse to the Internet routing table from theAT&T network's perspective.9route-server>Kerberos: No default realm defined for Kerberos!term len 0route-server>sh ip bgp sumBGP router identifier 10.1.2.5, local AS number 65000BGP table version is 1286647, main routing table version 1286647163458 network entries using 16509258 bytes of memory3370426 path entries using 161780448 bytes of memory37373 BGP path attribute entries using 2093112 bytes of memory33667 BGP AS-PATH entries using 879950 bytes of memory5 BGP community entries using 136 bytes of memory0 BGP route-map cache entries using 0 bytes of memory0 BGP filter-list cache entries using 0 bytes of memoryBGP using 181262904 total bytes of memoryDampening enabled. 1389 history paths, 994 dampened paths163353 received paths for inbound soft reconfigurationBGP activity 181085/17627 prefixes, 5037513/1667087 paths, scan interval 60 secsNeighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd10.0.0.2 4 7018 0 0 0 0 0 never Idle (Admin)12.0.1.63 4 7018 397245 12186 1286648 0 0 1w1d 012.123.1.236 4 7018 387448 12185 1286645 0 0 1w1d 16335312.123.5.240 4 7018 346180 12186 1286645 0 0 1w1d 16335212.123.9.241 4 7018 419257 12185 1286645 0 0 1w1d 16335312.123.13.241 4 7018 356320 12185 1286645 0 0 1w1d 16335412.123.17.244 4 7018 411677 12189 1286645 0 0 2d20h 16335412.123.21.243 4 7018 474681 12185 1286645 0 0 1w1d 16335112.123.25.245 4 7018 348068 12186 1286645 0 0 1w1d 16335312.123.29.249 4 7018 347119 12186 1286645 0 0 1w1d 16335412.123.33.249 4 7018 501231 12185 1286645 0 0 1w1d 16335212.123.37.250 4 7018 521938 12167 1286645 0 0 1d19h 16335410BGP table version is 1286649, local router ID is 10.1.2.5Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, S StaleOrigin codes: i - IGP, e - EGP, ? - incomplete Network From Reuse Path*d 193.178.117.0 12.123.9.241 00:01:30 7018 5400 5400 5400


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GT ECE 4110 - Border Gateway Protocol

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