diff options
Diffstat (limited to 'share/man')
| -rw-r--r-- | share/man/man4/gre.4 | 89 |
1 files changed, 42 insertions, 47 deletions
diff --git a/share/man/man4/gre.4 b/share/man/man4/gre.4 index d0d7c144f2a..5210c3ab889 100644 --- a/share/man/man4/gre.4 +++ b/share/man/man4/gre.4 @@ -1,4 +1,4 @@ -.\" $OpenBSD: gre.4,v 1.1 2000/01/07 22:28:03 angelos Exp $ +.\" $OpenBSD: gre.4,v 1.2 2000/01/08 02:12:47 angelos Exp $ .\" $NetBSD: gre.4,v 1.10 1999/12/22 14:55:49 kleink Exp $ .\" .\" Copyright 1998 (c) The NetBSD Foundation, Inc. @@ -47,9 +47,9 @@ .Tn GRE and .Tn MobileIP -is enabled with the following +are enabled with the following .Xr sysctl 3 -variables in +variables respectively in .Pa /etc/sysctl.conf : .Bl -tag -width xxxxxxxxxxxxxxxxxxxxx .It net.inet.gre.allow @@ -61,38 +61,37 @@ Allow MobileIP packets in and out of the system. .Sh DESCRIPTION The .Nm gre -network interface is a pseudo device that allows to encapsulate datagrams -into IP. These encapsulated datagrams are routed to a destination host, -where they are decapsulated and further routed to their final destination. -The so called ``tunnel'' appears to the inner datagrams like one hop. +network interface allows tunnel construction using the Cisco GRE or +the Mobile-IP (RFC 2004) encapsulation protocols. .Pp This driver currently supports the following modes of operation: .Bl -tag -width abc .It GRE encapsulation (IP protocol number 47). -Encapsulated datagrams are -prepended by a outer datagram and a GRE header. The GRE header specifies -the type of the encapsulated datagram and thus allows for tunneling other -protocols than IP like e.g. AppleTalk (not yet supported). GRE mode is -also the default tunnel mode on Cisco routers. This is also the default -mode of operation of the +Encapsulated datagrams are prepended by a outer datagram and a GRE header. +The GRE header specifies the type of the encapsulated datagram +and thus allows for tunneling other protocols than IP like +e.g. AppleTalk (not yet supported). +GRE mode is the default tunnel mode on Cisco routers. +This is also the default mode of operation of the .Sy gre Ns Ar X interfaces. .It MOBILE encapsulation (IP protocol number 55). -Datagrams are -encapsulated into IP, but with a shorter encapsulation. The original -IP header is modified and the modifications are inserted between the -so modified header and the original payload. Like IPIP only for IP in IP -encapsulation. +Datagrams are encapsulated into IP, but with a much smaller +encapsulation header. +This protocol only supports IP in IP encapsulation, and is intended +for use with mobile IP. .El .Pp The network interfaces are named .Sy gre Ns Ar 0 , -.Sy gre Ns Ar 1 -and so on, as many as have given on the +.Sy gre Ns Ar 1 , +etc. +The number of interfaces is given by the corresponding .Sy pseudo-device -line in the system config file. Each interface supports a number of -.Xr ioctl 2 Ns s, -such as: +line in the system config file. +.Xr gre 4 +interfaces support the following +.Xr ioctl 2 Ns s : .Bl -tag -width aaa .It GRESADDRS: Set the IP address of the local tunnel end. @@ -103,10 +102,9 @@ Query the IP address that is set for the local tunnel end. .It GREGADDRD: Query the IP address that is set for the remote tunnel end. .It GRESPROTO: -Set the operation mode to the specified IP protocol value. The -protocol is passed to the interface in (struct ifreq)->ifr_flags. -The operation mode can also -be given as +Set the operation mode to the specified IP protocol value. +The protocol is passed to the interface in (struct ifreq)->ifr_flags. +The operation mode can also be given as .Bl -tag -width bbb .It link0 IPPROTO_GRE @@ -117,7 +115,7 @@ IPPROTO_MOBILE to .Xr ifconfig 8 . As the linkN flags are not mutually exclusive, modes must be set by applying -positive and negative flags as e.g. +positive and negative flags, e.g., .Xr ifconfig 8 link0 -link1 -link2 .It GREGPROTO: @@ -141,7 +139,7 @@ Host X-- Host A ----------------tunnel---------- cisco D------Host E +------Host B----------Host C----------+ .Ed - On host A (NetBSD): + On host A (OpenBSD): # route add default B # ifconfig greN A D netmask 0xffffffff linkX up @@ -160,15 +158,13 @@ Host X-- Host A ----------------tunnel---------- cisco D------Host E OR - On Host D (NetBSD): + On Host D (OpenBSD): # route add default C # ifconfig greN D A .Pp -If all goes well, you should see packets flowing ;-) -.Pp -If you want to reach Host A over the tunnel (from the Cisco D), then -you have to have an alias on Host A for e.g. the Ethernet interface like: +To reach Host A over the tunnel (from host D), there has to be an +alias on Host A for the ethernet interface: ifconfig <etherif> alias Y and on the cisco ip route Y mask tunnelX @@ -177,16 +173,16 @@ For correct operation, the .Nm device needs a route to the destination, that is less specific than the one over the tunnel. -(Basically, there needs to be a route to the decapsulating host that -does not run over the tunnel, as this would be a loop ..) +(There needs to be a route to the decapsulating host that +does not run over the tunnel, as this would create a loop.) .Pp -In order to +In order for .Xr ifconfig 8 to actually mark the interface as up, the keyword ``up'' must be given last on its command line. .Pp -The kernel must be set to forward datagrams by either option -``GATEWAY'' in the kernel config file or by issuing the appropriate +The kernel must be set to forward datagrams by including option +``GATEWAY'' in the kernel config file and issuing the appropriate option to .Xr sysctl 8 . .Sh SEE ALSO @@ -204,20 +200,19 @@ A description of GRE encapsulation can be found in RFC 1701, RFC 1702. .Pp A description of MOBILE encapsulation can be found in RFC 2004. .Sh BUGS -The compute_route() code in if_gre.c toggles the last bit of the +The compute_route() code in net/if_gre.c toggles the last bit of the IP-address to provoke the search for a less specific route than the -one directly over the tunnel to prevent loops. This is possibly not -the best solution. +one directly over the tunnel to prevent loops. +This is possibly not the best solution. .Pp To avoid the address munging described above, turn on the link1 flag -on the ifconfig command line. This implies that the GRE packet -destination (set via greconfig -d) and the ifconfig remote host are -not the same IP addresses, and that the GRE destination does not route -over the greX interface itself. +on the ifconfig command line. +This implies that the GRE packet destination (set via greconfig -d) +and the ifconfig remote host are not the same IP addresses, and that +the GRE destination does not route over the greX interface itself. .Pp GRE RFC not yet fully implemented (no GRE options), no other protocols yet than IP over IP. - .Pp .Sh AUTHOR Heiko W.Rupp <hwr@pilhuhn.de> |