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* in diagrams, name routers as such

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* enhance formatting
 * add section headers for examples
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hubertf 2009-01-04 16:27:48 +00:00
parent befea92737
commit b007c29b93
1 changed files with 43 additions and 29 deletions
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share/man/man4/gre.4
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@ -1,4 +1,4 @@
.\" $NetBSD: gre.4,v 1.39 2008/05/10 09:33:31 martin Exp $
.\" $NetBSD: gre.4,v 1.40 2009/01/04 16:27:48 hubertf Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
@ -27,7 +27,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd December 4, 2006
.Dd January 4, 2009
.Dt GRE 4
.Os
.Sh NAME
@ -144,14 +144,16 @@ ones defined with
for the interface (as if IP is encapsulated), but need not be, as e.g. when
encapsulating AppleTalk.
.Sh EXAMPLES
.Ss Example 1: Basic GRE tunneling
Configuration example:
.Bd -literal
Host X-- Host A ----------------tunnel---------- cisco D------Host E
\\ |
Host X-- Router A --------------tunnel---------- Router D ----Host E
| |
\\ /
+------Host B----------Host C----------+
+----- Router B ----- Router C --------+
.Ed
On host A
.Pp
On Router A
.Pq Nx :
.Bd -literal
# route add default B
@ -160,7 +162,8 @@ On host A
# ifconfig greN tunnel A D
# route add E D
.Ed
On Host D (Cisco):
.Pp
On Router D (Cisco):
.Bd -literal
Interface TunnelX
ip unnumbered D ! e.g. address from Ethernet interface
@ -170,8 +173,8 @@ On Host D (Cisco):
ip route A mask C
ip route X mask tunnelX
.Ed
OR
On Host D
.Pp
or on Router D
.Pq Nx :
.Bd -literal
# route add default C
@ -182,16 +185,17 @@ On Host D
.Pp
If all goes well, you should see packets flowing ;-)
.Pp
If you want to reach Host A over the tunnel (from Host D (Cisco)), then
you have to have an alias on Host A for e.g. the Ethernet interface like:
If you want to reach Router A over the tunnel (from Router D (Cisco)), then
you have to have an alias on Router A for e.g. the Ethernet interface like:
.Bd -literal
ifconfig \*[Lt]etherif\*[Gt] alias Y
.Ed
and on the cisco
.Pp
and on the Cisco
.Bd -literal
ip route Y mask tunnelX
.Ed
.Pp
.Ss Example 2: Linking private subnets
A similar setup can be used to create a link between two private networks
(for example in the 192.168 subnet) over the Internet:
.Bd -literal
@ -200,11 +204,12 @@ A similar setup can be used to create a link between two private networks
\\ /
+----- the Internet ------+
.Ed
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
.Pp
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:
.Pp
On router A:
On Router A:
.Bd -literal
# ifconfig greN create
# ifconfig greN 192.168.1.1 192.168.2.1
@ -212,7 +217,7 @@ On router A:
# route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
.Ed
.Pp
On router B:
On Router B:
.Bd -literal
# ifconfig greN create
# ifconfig greN 192.168.2.1 192.168.1.1
@ -220,6 +225,7 @@ On router B:
# route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
.Ed
.Pp
.Ss Example 3: Encapsulating GRE in UDP
To setup the same tunnel as above, but using GRE in UDP encapsulation
instead of GRE encapsulation, set flags
.Ar link0
@ -227,7 +233,7 @@ and
.Ar link2 ,
and specify source and destination UDP ports.
.Pp
On router A:
On Router A:
.Bd -literal
# ifconfig greN create
# ifconfig greN link0 link2
@ -236,38 +242,46 @@ On router A:
# route add -net 192.168.2 -netmask 255.255.255.0 192.168.2.1
.Ed
.Pp
On router B:
On Router B:
.Bd -literal
# ifconfig greN create
# ifconfig greN link0 link2
# ifconfig greN 192.168.2.1 192.168.1.1
# ifconfig greN tunnel B,port-B A,port-A
# route add -net 192.168.1 -netmask 255.255.255.0 192.168.1.1
.Ed
.Pp
.Ss Example 4: Realizing IPv6 connectivity
Along these lines, you can use GRE tunnels to interconnect two IPv6
networks over an IPv4 infrastructure, or to hook up to the IPv6 internet
via an IPv4 tunnel to a Cisco router.
.Bd -literal
2001:db8:1::/64 -- NetBSD A -----tunnel----- Cisco B --- IPv6 Internet
2001:db8:1::/64 -- NetBSD A ---- Tunnel ---- Cisco B --- IPv6 Internet
\\ /
\\ /
+----- the Internet ------+
+------ the Internet ------+
.Ed
.Pp
The example will use the following addressing:
.Nx
A has the IPv4 address A and the IPv6 address 2001:db8:1::1 (connects
.Bl -hang
.It Nx A
has the IPv4 address A and the IPv6 address 2001:db8:1::1 (connects
to internal network 2001:db8:1::/64).
Cisco B has external IPv4 address B.
All the IPv6 internet world is behind B, so A wants to route 0::0/0
.It Cisco B
has external IPv4 address B.
.It All the IPv6 internet world
is behind B, so A wants to route 0::0/0
(the IPv6 default route) into the tunnel.
The GRE tunnel will use a transit network: 2001:db8:ffff::1/64 on
.It The GRE tunnel
will use a transit network: 2001:db8:ffff::1/64 on
the
.Nx
side, and ::2/64 on the Cisco side.
.El
.Pp
Then the following commands will configure the tunnel:
.Pp
On router A
On Router A
.Pq Nx :
.Bd -literal
# ifconfig greN create
@ -277,7 +291,7 @@ On router A
# route add -inet6 0::0/0 2001:db8:ffff::2 -ifp greN
.Ed
.Pp
On router B (Cisco):
On Router B (Cisco):
.Bd -literal
Interface TunnelX
tunnel mode gre ip