Border 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 well Source: TCP/IP Protocol Suite, by Fourouzan

Path Vector Routing Routing table entries consist of destination network, next router, autonomous system path to reach destination Example path vector routing table Destination Network Next Router Path N01 R07 AS5, AS19, AS21 N02 R10 AS14, AS8, AS7 N03 R2 AS4, AS9, AS6 N04 R3 AS1, AS2 Autonomous Boundary Routers advertise to their neighbors how to get to networks inside their own autonomous systems

BGP Types of Messages Types are: OPEN, UPDATE, KEEPALIVE,NOTIFICATION Packet Formats: All BGP packets have same common header: Marker 16 bytes Length 16 bits Type 8 bits Marker - Fields for authentication Length - Length of entire BGP message including common header shown here Type - Identifies which of the four message types this is.

My autonomous system 16 bits Open Message Use this message type to open a connection (TCP connection used) with neighbor Version 8 bits My autonomous system 16 bits Hold Time 16 bits BGP Identifier 32 bits Option Length Variable Length Option Type in common header = 1 Version - Version is 4 at present in the internet My Autonomous System - Autonomous System Number Hold Time - Max number of seconds before must receive update or a keep alive message or we consider other router dead BGP ID - Four byte IP of router sending Options

Unfeasible Routes Length 8 bits Update Message Used 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. Unfeasible Routes Length 8 bits Withdrawn Routes is of variable length Path Attribute Length 16 bits Variable Length Path Attributes Variable Length Network Layer Reachability Info Unfeasible Routes Length - Length of next field Withdrawn Routes - List of routes to remove Path Attributes Length - Length of next field Path Attributes - Info like ORIGIN: RIP, OSPF, etc generated route info;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 packet Network Layer Reachability Info - Network IP and number of bits in mask

Variable Length Error data Keep Alive Message The Routers exchange Keep Alive messages. (2 Minutes common) The message itself is just a common BGP Header Message with Type = 3 Notification Message Sent 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 bits Error Subcode 8 bits Variable Length Error data

spawn telnet route-server.ip.att.net Trying 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 routers throughout 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 above routers, providing a glimpse to the Internet routing table from the AT&T network's perspective.

route-server>Kerberos: No default realm defined for Kerberos! term len 0 route-server>sh ip bgp sum BGP router identifier 10.1.2.5, local AS number 65000 BGP table version is 1286647, main routing table version 1286647 163458 network entries using 16509258 bytes of memory 3370426 path entries using 161780448 bytes of memory 37373 BGP path attribute entries using 2093112 bytes of memory 33667 BGP AS-PATH entries using 879950 bytes of memory 5 BGP community entries using 136 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 181262904 total bytes of memory Dampening enabled. 1389 history paths, 994 dampened paths 163353 received paths for inbound soft reconfiguration BGP activity 181085/17627 prefixes, 5037513/1667087 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 10.0.0.2 4 7018 0 0 0 0 0 never Idle (Admin) 12.0.1.63 4 7018 397245 12186 1286648 0 0 1w1d 0 12.123.1.236 4 7018 387448 12185 1286645 0 0 1w1d 163353 12.123.5.240 4 7018 346180 12186 1286645 0 0 1w1d 163352 12.123.9.241 4 7018 419257 12185 1286645 0 0 1w1d 163353 12.123.13.241 4 7018 356320 12185 1286645 0 0 1w1d 163354 12.123.17.244 4 7018 411677 12189 1286645 0 0 2d20h 163354 12.123.21.243 4 7018 474681 12185 1286645 0 0 1w1d 163351 12.123.25.245 4 7018 348068 12186 1286645 0 0 1w1d 163353 12.123.29.249 4 7018 347119 12186 1286645 0 0 1w1d 163354 12.123.33.249 4 7018 501231 12185 1286645 0 0 1w1d 163352 12.123.37.250 4 7018 521938 12167 1286645 0 0 1d19h 163354

BGP table version is 1286649, local router ID is 10.1.2.5 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, S Stale Origin 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 5588 8246 34765 34765 34765 34765 34765 34765 i *d 12.174.7.0/24 12.123.17.244 00:01:40 7018 10428 i *d 193.178.117.0 12.123.13.241 00:01:50 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.134.124 00:02:00 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.33.249 00:02:00 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.25.245 00:01:50 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.29.249 00:01:50 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.196.111 00:01:50 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.37.250 00:02:00 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 193.178.117.0 12.123.145.124 00:02:00 7018 5400 5400 5400 5588 8246 34765 34765 34765 34765 34765 34765 i *d 129.66.0.0/18 12.123.139.124 00:02:40 7018 701 14793 14793 14793 3464 i *d 192.54.250.0 12.123.13.241 00:02:40 7018 16928 i *d 140.157.208.0/20 12.123.13.241 00:02:40 7018 16928 i *d 140.157.64.0/20 12.123.13.241 00:02:40 7018 16928 i *d 140.157.48.0/20 12.123.13.241 00:02:40 7018 16928 i *d 140.157.32.0/20 12.123.13.241 00:02:40 7018 16928 i *d 84.44.0.0/24 12.123.5.240 00:02:40 7018 3549 12713 9121 15924 i *d 84.44.0.0/24 12.123.45.252 00:02:40 7018 3549 12713 9121 15924 i *d 84.44.0.0/24 12.123.13.241 00:02:40 7018 3549 12713 9121 15924 i

* 222.255.224.0/19 12.123.37.250 0 7018 7473 7643 i * 12.123.139.124 0 7018 7473 7643 i * 12.123.145.124 0 7018 7473 7643 i * 12.123.45.252 0 7018 7473 7643 i * 12.123.17.244 0 7018 7473 7643 i * 12.123.41.250 0 7018 7473 7643 i *> 12.123.1.236 0 7018 7473 7643 i * 12.123.142.124 0 7018 7473 7643 i * 12.123.21.243 0 7018 7473 7643 i * 12.123.137.124 0 7018 7473 7643 i * 12.123.9.241 0 7018 7473 7643 i * 12.123.13.241 0 7018 7473 7643 i * 12.123.199.239 0 7018 7473 7643 i * 12.123.133.124 0 7018 7473 7643 i * 12.123.33.249 0 7018 7473 7643 i * 12.123.196.111 0 7018 7473 7643 i * 12.123.134.124 0 7018 7473 7643 i * 12.123.5.240 0 7018 7473 7643 i * 12.123.25.245 0 7018 7473 7643 i * 12.123.29.249 0 7018 7473 7643 i

route-server>term len 512 route-server>sh ip bgp BGP table version is 1286652, local router ID is 10.1.2.5 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path * 3.0.0.0 12.123.37.250 0 7018 701 703 80 i * 12.123.139.124 0 7018 701 703 80 i * 12.123.145.124 0 7018 701 703 80 i * 12.123.45.252 0 7018 701 703 80 i * 12.123.17.244 0 7018 701 703 80 i * 12.123.41.250 0 7018 701 703 80 i * 12.123.1.236 0 7018 701 703 80 i * 12.123.142.124 0 7018 701 703 80 i * 12.123.21.243 0 7018 701 703 80 i * 12.123.137.124 0 7018 701 703 80 i * 12.123.9.241 0 7018 701 703 80 i * 12.123.13.241 0 7018 701 703 80 i * 12.123.199.239 0 7018 701 703 80 i * 12.123.133.124 0 7018 701 703 80 i * 12.123.33.249 0 7018 701 703 80 i * 12.123.196.111 0 7018 701 703 80 i * 12.123.134.124 0 7018 701 703 80 i *> 12.123.5.240 0 7018 701 703 80 i * 12.123.25.245 0 7018 701 703 80 i * 12.123.29.249 0 7018 701 703 80 i * 4.0.0.0 12.123.37.250 0 7018 3356 i * 12.123.139.124 0 7018 3356 i * 12.123.145.124 0 7018 3356 i * 12.123.45.252 0 7018 3356 i

Two More Interconnection Techniques in Addition to BGP 1. Aggregation 2. Using Static and default routes Aggregation - routing domain is represented by a single IP prefix and router sits at the aggregation point. ( can have more than one router and aggregation point ).Only the aggregate is advertised out on backbone. Example aggregation network “ Interop Net 1997 ”. Class A 45.0.0.0/8 used in convention center. One aisle was one “Routing Information Base” RIB. Each RIB had a common /16 prefix for example 45.77.0.0/16 was “RIB 77. ” Subnet mask /22 used within each RIB So only a portion of each RIB was used. R 45.0.4.1 FDDI Back Bone 45.0.4.70 RP1 RP2 45.77.0.1 45.77.0.2 45.77.0.0/22 45.77.0.7 45.77.0.11 45.77.0.21 R R R 45.77.16.0/22 45.77.0.35 45.77.44.0/22 R R 45.77.32.0/22 45.77.20.0/22 45.77.96.0/22

RIPV1 was used on the RIB because all vendors routers implement RIPv1. OSPF was used on FDDI backbone. Routers RP1 and RP2 spoke both OSPF and RIPv1 RIB’s OSPF area ID was 45.77.0.0 and each RIB was a stub area. If an exhibitor wanted to run OSPF they could do so. Routers RP1 and RP2 advertised default route onto RIB so RIB attached routers had a way out to internet. Unnecessary to advertise any other routers onto RIB. All routers on RIB learn RIP routes from each other as will as default routers from backbone routers. Backbone routers RP1 and RP2 were configured (restricted) so they could only learn RIP Routes from the /22s within 45.77.0.0/16

Examples of valid /22 prefixes that are members of this “RIB 77”: 45.77.0.0/22 45.77.4.0/22 … 45.77.248.0/22 45.77.252.0/22 Back bone routers will know about specific routes inside 45.77.0.0/16 from RIP. Any /22 routes not within 45.77.0.0/16 will not be learned by this RIB. For example 45.101.88.0/22 should be learned only by routers on RIB 101 ( 45.101.0.0/16 ). With aggregation backbone routers RP1 and RP2 do not put in their routing tables every active /22 prefix from the other RIBs Backbone routers only advertised single aggregated prefix 45.77.0.0/16 on backbone. Thus RP1 and RP2 are know to be where other backbone routers should send traffic for 45.77... When a packet arrives at RP1 or RP2 they look at RIP learned routes from their attached RIB to decide how to forward packets.

Example Forwarding Table: Known Prefixes Next-Hop Gateway Metric Source ------------------------ ------------------------------ -------------------- ----------------- 0.0.0.0/0 45.0.4.1 10 OSPF 45.0.4.0/22 45.0.4.70 0 (connected) direct 45.60.0.0/16 45.0.4.60 6 OSPF 45.61.0.0/16 45.0.4.61 6 OSPF 45.62.0.0/16 45.0.4.62 6 OSPF 45.63.0.0/16 45.0.4.63 6 OSPF 45.77.0.0/22 45.77.0.1 0 ( connected ) direct 45.77.16.0/22 45.77.0.7 1 RIP 45.77.20.0/22 45.77.0.7 2 RIP 45.77.32.0/22 45.77.0.11 1 RIP 45.77.44.0/22 45.77.0.21 1 RIP 45.77.96.0/22 45.77.0.35 1 RIP

Which router contains the previous routing table? Since 45.77.0.1 0 (connected ) must be RP1 ( Primary Router for RIB 77 ) - Note that several / 16s were learned via OSPF via 45.0.4.0/22 interface which is the FDDI backbone. These are other RIB aggregates. Their internal structure is invisible to us. (each RIB is an OSPF area ) Note 5 routes learned from RIP and match the diagram drawn of the network. - If router RP1 gets packet with destination 45.77.96.171 it will be forwarded to 45.77.0.35