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Add example howto configure gre(4) tunnel with the same inner and

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outer addresses using multiple FIBs.

X-MFC after:	r282809
This commit is contained in:
ae 2015-06-02 00:47:38 +00:00
parent 7447f1a3e1
commit 96fb955fec
1 changed files with 39 additions and 1 deletions
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40
share/man/man4/gre.4
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@ -29,7 +29,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd November 7, 2014
.Dd June 2, 2015
.Dt GRE 4
.Os
.Sh NAME
@ -117,6 +117,44 @@ 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
.Ed
.Pp
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.
.Bd -literal
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)
.Ed
.Pp
On Host A (FreeBSD):
.Pp
First of multiple FIBs should be configured via loader.conf:
.Bd -literal -offset indent
net.fibs=2
net.add_addr_allfibs=0
.Ed
.Pp
Then routes to the gateway and remote tunnel endpoint via this gateway
should be added to the second FIB:
.Bd -literal -offset indent
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
.Ed
.Pp
And GRE tunnel should be configured to change FIB for encapsulated packets:
.Bd -literal -offset indent
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
.Ed
.Pp
.Sh NOTES
The MTU of
.Nm