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CS485G Spring 2015 63

(d) Unix sockets can be established for either UDP or TCP.

12. Internet components

(a) Backbone: collection of routers connected to each other by high-

capacity point-to-point networks. The US has about 50 commer-

cial backbones.

(b) Network Access Point (NAP): Router connecting multiple peer

backbones. The US has about 12 NAPs connecting commercial

backbones.

(d) Point of presence (POP): machine connected to the Internet.

(e) Lecture 36, 4/29/2015

(f) Internet service provider (ISP): provides access to POPs, by dial-

up, DSL, cable, T1 line, or some other technology.

13. Shortcomings of IPv4

(a) Messages are insecure: they are visible to routers (no read pro-

tection), the source address can be forged (no authentication),

and they can be modiﬁed in transit (no write protection).

(b) There aren’t enough IP addresses.

14. Techniques to deal with insufﬁcient addresses

(a) Dynamic (and temporary) allocation of addresses to POPs by

ISPs using the dynamic host conﬁguration protocol (DHCP).

The ISP only needs enough addresses to handle currently con-

nected POPs.

(b) Network-address translation (NAT): router assigns private ad-

dresses (such as 192.168.3.3) to POPs within its domain, and

it modiﬁes the headers of packets in both directions.

existing conversation.

15. IPv4 address space is divided into classes of regions

(a) Class A: ﬁrst octet in range 0-127. 2

addresses in region.

(b) Class B: ﬁrst octet in range 128-191; second octet 0-255. 2

ad-

dresses in region.

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Cirrus Logic CS485 Bedienungsanleitung Seite 63