Question? Leave a message!




Exterior Gateway Protocols

Exterior Gateway Protocols: EGP, BGP-4, CIDR and interior and exterior gateway routing protocols ppt and what are exterior gateway protocols
Dr.ShivJindal Profile Pic
Dr.ShivJindal,India,Teacher
Published Date:19-07-2017
Website URL
Comment
Exterior Gateway Protocols: EGP, BGP-4, CIDR Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Cores, Peers, and the limit of default routes  Autonomous systems & EGP  BGP4  CIDR: reducing router table sizes  Refs: Chap 10,14,15. Books: “Routing in Internet” by Huitema, “Interconnections” by Perlman, “BGP4” by Stewart, Sam Halabi, Danny McPherson, Internet Routing Architectures  Reading: Geoff Huston, Commentary on Inter-domain Routing in the Internet  Reference: BGP-4 Standards Document: In TXT  Reading: Norton, Internet Service Providers and Peering  Reading: Labovitz et al, Delayed Internet Routing Convergence  Reference: Paxson, End-to-End Routing Behavior in the Internet,  Reading: Interdomain Routing: Additional Notes: In PDF In MS Word  Reference Site: Griffin, Interdomain Routing Links Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2History: Default Routes: limits  Default routes = partial information  Routers/hosts w/ default routes rely on other routers to complete the picture.  In general routing “signposts” should be: Consistent, I.e., if packet is sent off in one direction then another direction should not be more optimal. Complete, I.e., should be able to reach all destinations Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Core  A small set of routers that have consistent & complete information about all destinations.  Outlying routers can have partial information provided they point default routes to the core Partial info allows site administrators to make local routing changes independently. CORE . . . S1 S2 Sm Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Peer Backbones  Initially NSFNET had only one connection to ARPANET (router in Pittsburg) = only one route between the two.  Addition of multiple interconnections = multiple possible routes = need for dynamic routing  Single core replaced by a network of peer backbones = more scalable Today there are over 30 backbones  Routing protocol at cores/peers: GGP - EGP- BGP-4 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Exterior Gateway Protocol (EGP)  A mechanism that allows non-core routers to learn routes from core (external routes) routers so that they can choose optimal backbone routes  A mechanism for non-core routers to inform core routers about hidden networks (internal routes)  Autonomous System (AS) has the responsibility of advertising reachability info to other ASs. One+ routers may be designated per AS. Important that reachability info propagates to core routers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Purpose of EGP you can reach net A via me AS2 EGP AS1 R3 R2 traffic to A R1 A table at R1: border router R dest next hop A R2 internal router Shivkumar Kalyanaraman RenssShare elaer Polytechnic Iconne nstitute ctivity information across ASes 7EGP Operation  Neighbor Acquisition: Reliable 2-way handshake  Neighbor Reachability:  Hellos: j out of m hellos OK = Neighbor UP  k out of n hellos NOT OK = Neighbor DOWN  Updates/Queries:  EGP is an incremental protocol. New info = send updates  Each router can query neighbors as well  Reachability advertized; metrics ignored  Requires a tree topology of ASes to avoid loops (eg: see next slide) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Why EGP Requires a Tree Structure.. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9EGP weaknesses  EGP does not interpret the distance metrics in routing update messages = cannot be compute shorter of two routes  As a result it restricts the topology to a tree structure, with the core as the root Rapid growth = many networks may be temporarily unreachable Only one path to destination = no load sharing  Need new protocol = BGP-4 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10Today’s Big Picture Large ISP Large ISP Stub Small ISP Dial-Up Access ISP Network Stub Stub Large number of diverse networks Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Internet AS Map: caida.org Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Autonomous System(AS)  Internet is not a single network Collection of networks controlled by different administrations  An autonomous system is a network under a single administrative control  An AS owns an IP prefix  Every AS has a unique AS number  ASes need to inter-network themselves to form a single virtual global network Need a common protocol for communication Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Intra-AS and Inter-AS routing C.b Gateways: B.a •perform inter-AS A.a routing amongst A.c b c themselves a a C •perform intra-AS b a B routers with other d routers in their AS c b A network layer inter-AS, link layer intra-AS physical layer routing in gateway A.c Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Who speaks Inter-AS routing? AS2 BGP AS1 R3 R2 R1 border router internal router R  Two types of routers  Border router(Edge), Internal router(Core)  Two border routers of different ASes will have a BGP Shivkumar Kalyanaraman session Rensselaer Polytechnic Institute 15Intra-AS vs Inter-AS  An AS is a routing domain  Within an AS:  Can run a link-state routing protocol  Trust other routers  Scale of network is relatively small  Between ASes:  Lack of information about other AS’s network (Link- state not possible)  Crossing trust boundaries  Link-state protocol will not scale  Routing protocol based on route propagation Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Autonomous Systems (ASes)  An autonomous system is an autonomous routing domain that has been assigned an Autonomous System Number (ASN). All parts within an AS remain connected. … the administration of an AS appears to other ASes to have a single coherent interior routing plan and presents a consistent picture of what networks are reachable through it. RFC 1930: Guidelines for creation, selection, and registration of an Autonomous System Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17IP Address Allocation and Assignment: Internet Registries IANA www.iana.org APNIC ARIN RIPE www.apnic.org www.arin.org www.ripe.org Allocate to National and local registries and ISPs Addresses assigned to customers by ISPs RFC 2050 - Internet Registry IP Allocation Guidelines RFC 1918 - Address Allocation for Private Internets RFC 1518 - An Architecture for IP Address Allocation with CIDR Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18AS Numbers (ASNs) ASNs are 16 bit values. 64512 through 65535 are “private” Currently over 11,000 in use. • Genuity: 1 • MIT: 3 • Harvard: 11 • UC San Diego: 7377 • AT&T: 7018, 6341, 5074, … • UUNET: 701, 702, 284, 12199, … • Sprint: 1239, 1240, 6211, 6242, … • … Shivkumar Kalyanaraman Rensselaer Polytechnic Institute ASNs represent units of routing policy 19Nontransit vs. Transit ASes Internet Service ISP 2 providers (ISPs) ISP 1 have transit networks NET A Nontransit AS Traffic NEVER might be a corporate flows from ISP 1 or campus network. through NET A to ISP 2 Could be a “content provider” Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20