1
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
2
Fig 4.11
3
Fig 4.13
IPv4, IP version 6 Internet Control Message Protocol (ICMP)
The Internet Protocol (IP)
4
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
5
Fig 4.15
6
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
7
Obtaining a host address– Manual configuration– Dynamic Host Configuration Protocol (DHCP)
8
9
Fig 4.21
Addressing, Routing, and Forwarding
10
Fig 4.22
11
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
12
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
13
Fig 4.24
14
Table 4.3
15
Error reporting Above IP Fig 4.25
ICMP
16
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
17
Fig 4.27
18
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)
19
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
20
Fig 4.35
21
Inter-AS routing: BGP– Path vector protocol– Exchange path information than cost information– Routing policy– On TCP
22
Fig 4.38 (router arch)
Fig 4.39 (input port)
Router
23
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
24
Fig 4.40 (switching fabric)
25
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.
26
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.
27
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
28
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
29
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
30
Fig 4.45
Fig 4.46
31
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
32
Fig 4.47
33
Fig 4.48
34
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
35
Fig 4.50
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