redes e serviços internet - ubingarcia/old/rsi1213/ubi 1011 rsi aula 9.pdf · • exemplos na...

Ano Lectivo 2012/2013 * 2º Semestre

Licenciatura em Engenharia Informática

Aula 9

UNIVERSIDADE DA BEIRA INTERIORFaculdade de EngenhariaDepartamento de Informática

Nuno M. Garcia, [email protected]

Redes e Serviços Internet (5388)

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Redes e Serviços Internet

• Agenda

• Não esquecer o trabalho teórico pedido

• Routing• (adaptado de Kurose, Computer Networking, e de http://netlab.ulusofona.pt; Murphy, University College Dublin, http://

www.csi.ucd.ie/Staff/jmurphy/networks/csd8_7-routing.pdf; Varadarajan, Virginia Tech, http://courses.cs.vt.edu/~cs5516/

spring03/slides/net_routing_1.pdf)

• outros assuntos?



• Estratégias para limitar o número de entradas numa tabela de routing:

• Routing por intervalos ou routing por classes (CIDR)

• Prefix matching




• Prefix matching

•




• Classless InterDomain Routing (CIDR)

• A zona de rede tem um comprimento arbitrário

• O formato usado é xxx.yyy.zzz.kkk / nn em que nn é o número de bits do endereço de rede

Redes e Serviços Internet (R)



• CIDR

The Internet Assigned Numbers Authority (IANA) issues to regional Internet registries (RIRs) large, short-prefix CIDR blocks. For example, 62.0.0.0/8, with over sixteen million addresses, is administered by RIPE NCC, the European RIR. The RIRs, each responsible for a single, large, geographic area, such as Europe or North America, then subdivide these blocks into smaller blocks and issue them local Internet registries. This subdividing process can be repeated several times at different levels of delegation. End user networks receive subnets sized according to the size of their network and projected short term need. Networks served by a single ISP are encouraged by IETF recommendations to obtain IP address space directly from their ISP. Networks served by multiple ISPs, on the other hand, may obtain provider-independent address space directly from the appropriate RIR.


For example, in the late 1990s, the IP address 208.130.29.33 (since reassigned) was used by www.freesoft.org. An analysis of this address identified three CIDR prefixes. 208.128.0.0/11, a large CIDR block containing over 2 million addresses, had been assigned by ARIN (the North American RIR) to MCI. Automation Research Systems, a Virginia VAR, leased an Internet connection from MCI and was assigned the 208.130.28.0/22 block, capable of addressing just over 1000 devices. ARS used a /24 block for its publicly accessible servers, of which 208.130.29.33 was one.

All of these CIDR prefixes would be used, at different locations in the network. Outside of MCI's network, the 208.128.0.0/11 prefix would be used to direct to MCI traffic bound not only for 208.130.29.33, but also for any of the roughly two million IP addresses with the same initial 11 bits. Within MCI's network, 208.130.28.0/22 would become visible, directing traffic to the leased line serving ARS. Only within the ARS corporate network would the 208.130.29.0/24 prefix have been used. (in Wikipedia.org)




in IP in Modern Networks, www.TelecomsAcademy.com



• Dois tipos fundamentais de intra-domain routing

• Link state

• Distance vector

• Há outros algoritmos para inter-domain routing (routing entre Autonomous Systems - AS)

• Um algoritmo de routing tem que ser:

• correcto, óptimo, eficiente, robusto, estável, justo (fairness), simples

• escalável?





• Link state

• Cada router troca informação com todos os routers da rede sobre os seus vizinhos, quando há uma mudança no estado da rede;

• vizinhos=routers que estão directamente ligados

• há inundação (flood) da informaçao na rede

• mudança=se um router vizinho não responde a uma mensagem

• Distance vector





• Link state• Cada router troca informação com todos os routers da rede sobre os seus vizinhos, quando há uma mudança no estado da rede;

• vizinhos=routers que estão directamente ligados

• há inundação (flood) da informaçao na rede

• mudança=se um router vizinho não responde a uma mensagem

• Distance vector

• cada router troca informações de toda a rede com os seus vizinhos, em intervalos regulares (e.g. a cada 30 segundos)




• Distance-vector routing

• usado inicialmente na Arpanet, usado na Internet de hoje como RIP (Routing Information Protocol)

• uma variação deu origem ao BGP (Border Gateway Protocol), que determina as rotas entre Autonomous Systems (AS); Um AS é uma parte da Internet gerida por uma entidade, e.g. a rede da FCCN é um AS

• o custo por link pode ser diferente de 1




• problemas conhecidos em Distance-vector routing

• em algumas condições, pode ocorrer o count-to-infinity

• baixa convergência

• baixa fidelidade quando há falhas de links, uma vez que o router só informa os seus vizinhos.




• Link-State routing tenta resolver os problemas do Distance-Vector

•




• Os algoritmos de Link-State tem várias características interessantes:

• rápida convergência

• geram pouco tráfego

• respondem rapidamente a mudanças no estado dos links

• Exemplos na Internet de hoje: OSPF (Open Shortest Path First), IS-IS (Intermediate System to Intermediate System).

• Problemas:

• o Dijkstra é muito pesado para processadores de routers,

• se houver muitas mudanças, há muitas actualizações e isso é mau,

• usa-se um reliable flooding para os pacotes de link-state.




• Autonomous system (Internet)From Wikipedia, the free encyclopedia

Within the Internet, an Autonomous System (AS) is a collection of connected Internet Protocol (IP) routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet.[1]

Originally, the definition required control by a single entity, typically an Internet service provider or a very large organization with independent connections to multiple networks, that adhere to a single and clearly defined routing policy, as originally defined in RFC 1771.[2] The newer definition in RFC 1930 came into use because multiple organizations can runBGP using private AS numbers to an ISP that connects all those organizations to the Internet. Even though there may be multiple Autonomous Systems supported by the ISP, the Internet only sees the routing policy of the ISP. That ISP must have an officially registered Autonomous System Number (ASN).

A unique ASN is allocated to each AS for use in BGP routing. AS numbers are important because the ASN uniquely identifies each network on the Internet.

Until 2007, AS numbers were defined as 16-bit integers, which allowed for a maximum of 65536 assignments. The Internet Assigned Numbers Authority (IANA) has designated AS numbers 64512 through 65534 to be used for private purposes. The ASNs 0, 56320–64511, and 65535 are reserved by the IANA and should not be used in any routing environment. ASN 0 may be used to label non-routed networks. All other ASNs (1–54271) are subject to assignment by IANA, and, as of September 9, 2008, only 49152–54271 remained unassigned. RFC 4893 introduced 32-bit AS numbers, which IANA has begun to allocate. These numbers are written either as simple integers, or in the form x.y, where x and y are 16-bit numbers. Numbers of the form 0.y are exactly the old 16-bit AS numbers, 1.y numbers and 65535.65535 are reserved, and the remainder of the space is available for allocation.[3]The accepted textual representation of Autonomous System Numbers is defined in RFC 5396.[4]

The number of unique autonomous networks in the routing system of the Internet exceeded 5000 in 1999, 30000 in late 2008, and 35000 in mid 2010.[5

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• Na próxima semana, Aplicações Internet!

• Questões?


redes e serviços internet - ubingarcia/old/rsi1213/ubi 1011 rsi aula 9.pdf · • exemplos na...

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