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![Page 1: 1 o Two issues in practice – Scale – Administrative autonomy o Autonomous system (AS) or region o Intra autonomous system routing protocol o Gateway routers.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d825503460f94a6880c/html5/thumbnails/1.jpg)
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Two issues in practice– Scale– Administrative autonomy
Autonomous system (AS) or region Intra autonomous system routing protocol Gateway routers Inter-autonoumous system routing protocol
Hierarchical routing
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Fig 4.11
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Fig 4.13
IPv4, IP version 6 Internet Control Message Protocol (ICMP)
The Internet Protocol (IP)
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IPv4 addressing– An IP address is associated with an interface rather than with the host
or router containing the interface.– 32 bits long– Dotted-decimal notation (pp. 322)– Fig 4.14
– 223.1.1.0/24 where /24 -> a network mask, network prefix, an IP network, a network
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Fig 4.15
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Classful addressing: A, B, C, D Fig 4.17
Classless Interdomain Routing (CIDR): e.g., a.b.c.d/21 for 2000 hosts
Corporation for Assigned Names and Numbers (ICANN)– Allocate IP address– Manage the DNS root servers– Assign domain names– Resolve domain name disputes
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Obtaining a host address– Manual configuration– Dynamic Host Configuration Protocol (DHCP)
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Fig 4.21
Addressing, Routing, and Forwarding
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Fig 4.22
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Fig 4.23
Type of service: differentiated service (e.g., Cisco) IPv6: no fragmentation at routers Why does TCP/IP perform error checking at the both layers? IP options were dropped in the IPv6 header.
IPv4 datagram format
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MTU(max transfer unit): max amount of data that a link-layer packet can carry, e.g., 1,500 bytes for Ethernet, 576 bytes for wide-area links
Fragment The designers of IPv4 decided to put the job of datagram reass
embly in the end systems rather than in network routers.
IP datagram fragmentation
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Fig 4.24
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Table 4.3
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Error reporting Above IP Fig 4.25
ICMP
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For a newly arriving host, the DHCP does– DHCP server discovery: broadcasting– DHCP server offer(s): the proposed IP address for the client, the ne
twork mask, and an IP address lease time– DHCP request– DHCP ACK
From a mobility aspect, how about DHCP?
DHCP
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Fig 4.27
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The NAT-enabled router does not run an Inter-AS routing protocol.
The NAT-enabled router behaves to the outside world as a single device with a single IP address. (port numbers)
Fig 4.28
Network Address Translators (NATs)
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Intra-AS routing: RIP and OSPF Routing Information Protocol
– Distance vector protocol– Hop count as a cost metric– Max cost of a path: 15– Every 30 seconds for RIP advertisements
Open Shortest Path First– Link state protocol– Once every 30 minutes– Adv.: security, multiple same-cost paths, integrated support for uni
cast and multicast routing, and support for hierarchy within a single routing domain.
Routing in the Internet
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Fig 4.35
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Inter-AS routing: BGP– Path vector protocol– Exchange path information than cost information– Routing policy– On TCP
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Fig 4.38 (router arch)
Fig 4.39 (input port)
Router
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Given the need to operate at today’s high link speeds, a number of ways to find out an appropriate forwarding table entry.
– A linear search– Store the forwarding table entries in a tree data structure– Content addressable memories– Forwarding table entries in a cache
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Fig 4.40 (switching fabric)
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Fig 4.41 (output ports)
Packet queues at both the input ports and the output ports -> packet loss depending on the traffic load, the relative speed of the switching fabric, and the line speed.
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Fig 4.42
Packet scheduler: choose one packet among queued for transmission
– First-come-first-served (FCFS) scheduling– Weighted fair queueing (WFQ)– Important for quality-of-service guarantees.
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Drop a packet before the buffer is full in order to provide a congestion signal to the sender -> active queue management (Random Early Detection (RED))
Head-of-the-line (HOL) blocking in an input-queued switch Fig 4.43
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Changes in IPv6– Expanded addressing capabilities (32 to 128 bits), anycast address– A streamlined 40-bute header– Flow labeling and priority– Fig 4.44
IPv6
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IPv6 vs IPv4– Fragmentation/reassembly: IPv6 does not allow for fragmentation
and reassembly at intermediate routers.– Header checksum: IPv4 header checksum needed to be recompute
d at every router.– Options: next headers pointer in IPv6
ICMP for IPv6– Packet too big, unrecognized IPv6 options error codes– IGMP
Transitioning from IPv4 to IPv6– Flag day– Dual-stack: DNS to determine whether another node is IPv6 or IPv4– Tunneling
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Fig 4.45
Fig 4.46
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Unicast vs multicast The sending of a packet from one sender to multiple receivers
with a single send operation. Network-layer aspects of multicast Handle multicast groups
– One-to-all unicast– Application-level multicast– Explicit multicast at the network layer
How to identify the receivers of a multicast datagram?– Address indirection: a single identifier is used for the group of rec
eivers -> class D and how to address a datagram sent to these receivers?
Multicast routing
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Fig 4.47
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Fig 4.48
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IGMP– Group membership protocol– Locally between a host and an attached router– Means for a host to inform its attached router that an application ru
nning one the host wants to join a specific multicast group– Joining a multicast group is receiver-driven
Network-layer multicast algorithms (PIM, DVMRP, MOSPF)– Coordinate the multicast routers so that multicast datagrams are r
outed to their final destinations Table 4.4
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Fig 4.50