projects / unix-history / blame
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1 | .\" Copyright (c) 1986 Regents of the University of California. |
| 2 | .\" All rights reserved. The Berkeley software License Agreement | |
| 3 | .\" specifies the terms and conditions for redistribution. | |
| 4 | .\" | |
| 2577f725 | 5 | .\" @(#)e.t 6.2 (Berkeley) %G% |
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6 | .\" |
| 7 | .\".ds RH "Network configuration options | |
| 8 | .bp | |
| 9 | .LG | |
| 10 | .B | |
| 11 | .ce | |
| 12 | APPENDIX E. NETWORK CONFIGURATION OPTIONS | |
| 13 | .sp | |
| 14 | .R | |
| 15 | .NL | |
| 16 | .PP | |
| 2577f725 | 17 | The network support in the kernel is self-configuring |
| 57349e41 MK |
18 | according to the protocol support options (INET and NS) and the network |
| 19 | hardware discovered during autoconfiguration. | |
| 20 | There are several changes that may be made to customize network behavior | |
| 21 | due to local restrictions. | |
| 22 | Within the Internet protocol routines, the following options | |
| 23 | set in the system configuration file are supported: | |
| 24 | .IP \fBGATEWAY\fP | |
| 25 | .br | |
| 26 | The machine is to be used as a gateway. | |
| 27 | This option currently makes only minor changes. | |
| 28 | First, the size of the network routing hash table is increased. | |
| 29 | Secondly, machines that have only a single hardware network interface | |
| 30 | will not forward IP packets; without this option, they will also refrain | |
| 31 | from sending any error indication to the source of unforwardable packets. | |
| 32 | Gateways with only a single interface are assumed to have missing | |
| 33 | or broken interfaces, and will return ICMP unreachable errors to hosts | |
| 34 | sending them packets to be forwarded. | |
| 35 | .IP \fBTCP_COMPAT_42\fP | |
| 36 | .br | |
| 37 | This option forces the system to limit its initial TCP sequence numbers | |
| 38 | to positive numbers. | |
| 39 | Without this option, 4.3BSD systems may have problems with TCP connections | |
| 40 | to 4.2BSD systems that connect but never transfer data. | |
| 41 | The problem is a bug in the 4.2BSD TCP; this option should be used | |
| 42 | during the period of conversion to 4.3BSD. | |
| 43 | .IP \fBIPFORWARDING\fP | |
| 44 | .br | |
| 45 | Normally, 4.3BSD machines with multiple network interfaces | |
| 46 | will forward IP packets received that should be resent to another host. | |
| 47 | If the line ``options IPFORWARDING="0"'' is in the system configuration | |
| 48 | file, IP packet forwarding will be disabled. | |
| 49 | .IP \fBIPSENDREDIRECTS\fP | |
| 50 | .br | |
| 51 | When forwarding IP packets, 4.3BSD IP will note when a packet is forwarded | |
| 52 | using the same interface on which it arrived. | |
| 53 | When this is noted, if the source machine is on the directly-attached | |
| 54 | network, an ICMP redirect is sent to the source host. | |
| 55 | If the packet was forwarded using a route to a host or to a subnet, | |
| 56 | a host redirect is sent, otherwise a network redirect is sent. | |
| 57 | The generation of redirects may be inhibited with the configuration | |
| 58 | option ``options IPSENDREDIRECTS="0".'' | |
| 59 | .br | |
| 60 | .IP \fBSUBNETSARELOCAL\fP | |
| 61 | TCP calculates a maximum segment size to use for each connection, | |
| 62 | and sends no datagrams larger than that size. | |
| 63 | This size will be no larger than that supported on the outgoing | |
| 64 | interface. | |
| 65 | Furthermore, if the destination is not on the local network, | |
| 66 | the size will be no larger than 576 bytes. | |
| 67 | For this test, other subnets of a directly-connected subnetted | |
| 68 | network are considered to be local unless the line | |
| 69 | ``options SUBNETSARELOCAL="0"'' is used in the system configuration file. | |
| 70 | .IP \fBCOMPAT_42\fP | |
| 71 | .br | |
| 72 | This option, intended as a catchall for 4.2BSD compatibility options, | |
| 73 | has only a single function thus far. | |
| 74 | It disables the checking of UDP input packet checksums. | |
| 75 | As the calculation of UDP packet checksums was incorrect in 4.2BSD, | |
| 76 | this option allows a 4.3BSD system to receive UDP packets from | |
| 77 | a 4.2BSD system. | |
| 78 | .LP | |
| 79 | The following options are supported by the Xerox NS protocols: | |
| 80 | .IP \fBNSIP\fP | |
| 81 | .br | |
| 82 | This option allows NS IDP datagrams to be encapsulated in Internet IP | |
| 83 | packets for transmission to a collaborating NSIP host. | |
| 84 | This may be used to pass IDP packets through IP-only link layer networks. | |
| 85 | See | |
| 86 | .IR nsip (4P) | |
| 87 | for details. | |
| 88 | .IP \fBTHREEWAYSHAKE\fP | |
| 89 | .br | |
| 90 | The NS Sequenced Packet Protocol does not require a three-way handshake | |
| 91 | before considering a connection to be in the established state. | |
| 92 | (A three-way handshake consists of a connection request, an acknowledgement | |
| 93 | of the request along with a symmetrical opening indication, | |
| 94 | and then an acknowledgement of the reciprocal opening packet.) | |
| 95 | This option forces a three-way handshake before data may be transmitted | |
| 96 | on Sequenced Packet sockets. |