svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
gre(4)
GRE(4) BSD Kernel Interfaces Manual GRE(4)
NAME
gre — encapsulating network device
SYNOPSIS
To compile the driver into the kernel, place the following line in the
kernel configuration file:
device gre
Alternatively, to load the driver as a module at boot time, place the
following line in loader.conf(5):
if_gre_load="YES"
DESCRIPTION
The gre network interface pseudo device encapsulates datagrams into IP.
These encapsulated datagrams are routed to a destination host, where they
are decapsulated and further routed to their final destination. The
“tunnel” appears to the inner datagrams as one hop.
gre interfaces are dynamically created and destroyed with the ifconfig(8)
create and destroy subcommands.
This driver corresponds to RFC 2784. Encapsulated datagrams are
prepended an 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. GRE mode is also the default tunnel mode on Cisco
routers. gre also supports Cisco WCCP protocol, both version 1 and ver‐
sion 2.
The gre interfaces support a number of additional parameters to the
ifconfig(8):
grekey Set the GRE key used for outgoing packets. A value of 0
disables the key option.
enable_csum Enables checksum calculation for outgoing packets.
enable_seq Enables use of sequence number field in the GRE header for
outgoing packets.
EXAMPLES
192.168.1.* --- Router A -------tunnel-------- Router B --- 192.168.2.*
\ /
\ /
+------ the Internet ------+
Assuming router A has the (external) IP address A and the internal
address 192.168.1.1, while router B has external address B and internal
address 192.168.2.1, the following commands will configure the tunnel:
On router A:
ifconfig greN create
ifconfig greN inet 192.168.1.1 192.168.2.1
ifconfig greN inet tunnel A B
route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
On router B:
ifconfig greN create
ifconfig greN inet 192.168.2.1 192.168.1.1
ifconfig greN inet tunnel B A
route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
In case when internal and external IP addresses are the same, different
routing tables (FIB) should be used. The default FIB will be applied to
IP packets before GRE encapsulation. After encapsulation GRE interface
should set different FIB number to outgoing packet. Then different FIB
will be applied to such encapsulated packets. According to this FIB
packet should be routed to tunnel endpoint.
Host X -- Host A (198.51.100.1) ---tunnel--- Cisco D (203.0.113.1) -- Host E
\ /
\ /
+----- Host B ----- Host C -----+
(198.51.100.254)
On Host A (FreeBSD):
First of multiple FIBs should be configured via loader.conf:
net.fibs=2
net.add_addr_allfibs=0
Then routes to the gateway and remote tunnel endpoint via this gateway
should be added to the second FIB:
route add -net 198.51.100.0 -netmask 255.255.255.0 -fib 1 -iface em0
route add -host 203.0.113.1 -fib 1 198.51.100.254
And GRE tunnel should be configured to change FIB for encapsulated pack‐
ets:
ifconfig greN create
ifconfig greN inet 198.51.100.1 203.0.113.1
ifconfig greN inet tunnel 198.51.100.1 203.0.113.1 tunnelfib 1
NOTES
The MTU of gre interfaces is set to 1476 by default, to match the value
used by Cisco routers. This may not be an optimal value, depending on
the link between the two tunnel endpoints. It can be adjusted via
ifconfig(8).
For correct operation, the gre device needs a route to the decapsulating
host that does not run over the tunnel, as this would be a loop.
The kernel must be set to forward datagrams by setting the
net.inet.ip.forwarding sysctl(8) variable to non-zero.
SEE ALSO
gif(4), inet(4), ip(4), me(4), netintro(4), protocols(5), ifconfig(8),
sysctl(8)
A description of GRE encapsulation can be found in RFC 2784 and RFC 2890.
AUTHORS
Andrey V. Elsukov <ae@FreeBSD.org>
Heiko W.Rupp <hwr@pilhuhn.de>
BUGS
The current implementation uses the key only for outgoing packets.
Incoming packets with a different key or without a key will be treated as
if they would belong to this interface.
The sequence number field also used only for outgoing packets.
BSD June 2, 2015 BSD