Chapter 2

2.1	Visit http://www.iana.org/numbers.htm and find the registry called "IP Version Number." Version 0 is reserved, versions 1–3 are unassigned, and version 5 is the Internet Stream Protocol.
2.2	All RFCs are available at no charge through electronic mail, anonymous FTP, or the Web. A starting point is http://www.ietf.org. The directory ftp://ftp.rfc-editor.org/in-notes is one location for RFCs. To start, fetch the current RFC index, normally the file rfc-index.txt, also available in an HTML version at http://www.rfc-editor.org/rfc-index.html. If we search the RFC index (see the solution to the previous exercise) with an editor of some form, looking for the term "Stream," we find that RFC 1819 defines Version 2 of the Internet Stream Protocol. Whenever looking for information that might be covered by an RFC, the RFC index should be searched.
2.3	With IPv4, this generates a 576-byte IP datagram (20 bytes for the IPv4 header and 20 bytes for the TCP header), the minimum reassembly buffer size with IPv4.
2.4	In this example, the server performs the active close, not the client.
2.5	The host on the token ring cannot send packets with more than 1,460 bytes of data because the MSS it received was 1,460. The host on the Ethernet can send packets with up to 4,096 bytes of data, but it will not exceed the MTU of the outgoing interface (the Ethernet) to avoid fragmentation. TCP cannot exceed the MSS announced by the other end, but it can always send less than this amount.
2.6	The "Protocol Numbers" section of the Assigned Numbers Web page (http://www.iana.org/numbers.htm) shows a value of 89 for OSPF.
2.7	A selective acknowledgment only indicates that the data covered by the sequence numbers reflected in the selective acknowledgment message was received. Only a cumulative acknowledgment says that the data up to and including the sequence number in the cumulative acknowledgment message was received. When freeing data from the send buffer based on a selective acknowledgment, the system may only free the exact data that was acknowledged, and not any before or after the selective acknowledgment.