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ECE544_Lec5_DR08 - ECE544 Communication Networks-II Spring...

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ECE544: Communication Networks-II, Spring 2008 D. Raychaudhuri Lecture 5 Includes teaching materials from L. Peterson, J. Kurose, K. Almeroth
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Today’s Lecture Scalable Addressing  Sub-netting Super-netting (CIDR) Route Aggregation Examples BGP Global Internet routing BGP protocol outline Multicast General discussion  Internet Group Management Protocol (IGMP) Routing Protocols – MOSPF, PIM
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Scalable IP Routing
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Internet Structure Recent Past NSFNET backbone Stanford BARRNET regional Berkeley P ARC NCAR UA UNM Westnet regional UNL KU ISU MidNet regional
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Internet Structure Today Backbone service provider Peering point Peering point Large corporation Large corporation Small corporation “Consumer ” ISP “Consumer” ISP Consumer” ISP
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IP Address 0 network host 10 network host 110 network host 1110 multicast address A B C D class 1.0.0.0 to 127.255.255.255 128.0.0.0 to 191.255.255.255 192.0.0.0 to 223.255.255.255 224.0.0.0 to 239.255.255.255 32 bits “class-full” addressing:
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How to Make Routing Scale Flat versus Hierarchical Addresses Inefficient use of Hierarchical Address Space class C with 2 hosts (2/255 = 0.78% efficient) class B with 256 hosts (256/65535 = 0.39%  efficient) Still Too Many Networks routing tables do not scale route propagation protocols do not scale
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Subnetting Add another level to address/routing hierarchy:  subnet Subnet masks  define variable partition of host part Subnets visible only within site Network number Host number Class B address Subnet mask (255.255.255.0) Subnetted address 111111111111111111111111 00000000 Network number Host ID Subnet ID
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Subnet Example Forwarding table at router R1 Subnet Number  Subnet Mask        Next Hop 128.96.34.0        255.255.255.128  interface 0 128.96.34.128    255.255.255.128  interface 1 128.96.33.0        255.255.255.0      R2 Subnet mask: 255.255.255.128 Subnet number: 128.96.34.0 128.96.34.15 128.96.34.1 H1 R1 128.96.34.130 Subnet mask: 255.255.255.128 Subnet number: 128.96.34.128 128.96.34.129 128.96.34.139 R2 H2 128.96.33.1 128.96.33.14 Subnet mask: 255.255.255.0 Subnet number: 128.96.33.0 H3
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Super-netting (CIDR) Class addressing doesn’t match real  needs: Class C is 255 addresses, too small Clsss B is 64K addresses, too big Need method of allocating addresses in  multiple sizes Assign block of contiguous network  numbers to nearby networks Called  CIDR C lassless  I nter- D omain  R outing
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Supernetting (CIDR) Assign block of contiguous network numbers  to nearby networks Called CIDR: Classless Inter-Domain Routing Protocol uses a (length, value) pair length = # of bits in network prefix Use CIDR bit mask to identify block size All routers must understand CIDR addressing Routers can aggregate routes with a single  advertisement -> use longest prefix match
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Supernetting (CIDR) Routers can aggregate routes with a single  advertisement -> use longest prefix match Hex/length notation for CIDR address: C4.50.0.0/12  denotes a netmask with 12 leading 1  bits, i.e.  FF.F0.0.0
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