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I am having problem setup the L2 over GRE tunnel with above hyperlink.

The following is the setup commands I used to setup GRE tunnel.

create and enable the GRE tunnel:

   > ip link add gre0 type gretap remote (CM WAN IP) local (GRE Eth1)
   > ifconfig gre0 up                                 

bridge create, add interface and enable:

   > brctl addbr br0
   >  ifconfig br0 up
   > brctl addif br0 gre0
   > brctl addif br0 eth2

add route for CM’s receive after de-encapsulation

  > ip route add 192.168.27.0/24 dev eth1

The problem was :

  1. CPE1 (00-0A-79-9F-60-AF) would send a DHCP discover out via GRE tunnel to DHCP server. (eth1 -> gre0 -> br0 -> eth2)
  2. DHCP offer is seen at eth2, br0, and gre0, but not at eth1 (eth2 -> br0 -> gre0 -> eth1)
  3. It seems like the DHCP offer is dropped before it is going out to eth1 with encapsulated (GRE capsule).

Can anyone give me a tip what could possibly went wrong with my settings??

MY "uname -a" is

 Linux x1-6-00-10-dc-b0-95-b7 3.2.0-29-generic-pae #46-Ubuntu SMP Fri Jul 27 17:25:43 UTC 2012 i686 i686 i386 GNU/Linux

The "ip link show" after tunnel is set

 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 00:40:05:00:00:28 brd ff:ff:ff:ff:ff:ff
 3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:10:dc:b0:95:b7 brd ff:ff:ff:ff:ff:ff
 4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master br0 state UP qlen 1000
link/ether 00:05:5d:01:be:f9 brd ff:ff:ff:ff:ff:ff
 6: gre0@NONE: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1462 qdisc pfifo_fast master br0 state UNKNOWN qlen 1000
link/ether ae:b7:f8:23:94:36 brd ff:ff:ff:ff:ff:ff
 7: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1462 qdisc noqueue state UP 
link/ether 00:05:5d:01:be:f9 brd ff:ff:ff:ff:ff:ff
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1 Answer

I don't think you can do this. GRE (like IP-in-IP, and SIT) is a layer-3 tunneling technology. It moves IP packets, not Ethernet frames. As such, it shouldn't be possible to bridge it (a layer-2 concept) with an Ethernet port.

If you want to bridge a tunnel, you would need to use a layer-2 tunneling technology that moves Ethernet-compatible frames like L2TP.

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