[ovs-discuss] Single-sided tunnel

Rodrigo Ruas Oliveira ruasoliveira at inf.ufrgs.br
Thu Jan 26 15:21:17 UTC 2017

Hello all,

I'd like to verify if what I'm trying to do is possible.

I'm trying to use tunnels to perform load balancing, just as it's done with
VLB. The idea is to send packets to an intermediary node which acts as
proxy and deflects the packet to its intended destination.

As I understand, ovs does not support IP-in-IP, only GRE and VXLAN, is that

So anyway, I've attempted to create a GRE interface within an OVS switch
which encapsulates a packet with an outer IPv4 header and sends it to a
router (which owns that IP). The router, then, should decapsulate the
packet and send it to the next-hop using the inner IPv4 header.

I'm using the following topology on mininet:

                (    (
                              < R1 >
                             /      \
           < X1 > -- < OVS 1 > ----- < OVS 2 > -- < X2 >
(                                    (

I first validated the topology and configs by running L2Learning on both
switches. This checked and everyone found everyone.

Next, I created a GRE port pointing to R1's IP on the R1-to-OVS1
interface (r1-eth0
-- s1-eth1) using:

sh ovs-vsctl add-port s1 s1-gre0 -- set interface s1-gre0 type=gre

and then reconfigure OVS1 to forward packets from X1 to the s1-gre0
interface. The result is a blackhole, packets never leave S1. Is this
expected? Should I be connecting s1-gre0 to s1-eth1 or another switch port
internally somehow?

Bellow, there is a dump of OVS1's flow table and ports. Ports 1, 2, and 3
connect to, respectively,  R1, S2, and X1. Port 4 is the GRE port.

The list of MAC addresses are:
R1: c2:e7:ba:8e:c8:d8
X1: 4a:cb:6a:d6:78:84
X2: 7a:73:b3:8f:b0:bf

mininet> sh ovs-ofctl dump-flows s1
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=1058.311s, table=0, n_packets=8, n_bytes=616,
idle_age=1015, priority=2,in_port=3 actions=output:4
 cookie=0x0, duration=1058.311s, table=0, n_packets=0, n_bytes=0,
idle_age=1058, priority=1,dl_dst=c2:e7:ba:8e:c8:d8 actions=output:1
 cookie=0x0, duration=1058.311s, table=0, n_packets=3, n_bytes=238,
idle_age=1015, priority=1,dl_dst=4a:cb:6a:d6:78:84 actions=output:3
 cookie=0x0, duration=1058.311s, table=0, n_packets=2, n_bytes=84,
idle_age=1006, priority=1,dl_dst=7a:73:b3:8f:b0:bf actions=output:2
 cookie=0x0, duration=1058.312s, table=0, n_packets=3, n_bytes=126,
idle_age=1006, priority=3,dl_dst=ff:ff:ff:ff:ff:ff actions=ALL

mininet> sh ovs-ofctl show s1
OFPT_FEATURES_REPLY (xid=0x2): dpid:0000000000000001
n_tables:254, n_buffers:256
 1(s1-eth1): addr:96:6e:1e:4e:d4:c3
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 2(s1-eth2): addr:e6:06:80:f5:31:63
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 3(s1-eth3): addr:ca:b1:3e:7d:f4:92
     config:     0
     state:      0
     current:    10GB-FD COPPER
     speed: 10000 Mbps now, 0 Mbps max
 4(s1-gre0): addr:de:10:c3:ae:d3:40
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max
 LOCAL(s1): addr:da:9e:08:55:b7:45
     config:     PORT_DOWN
     state:      LINK_DOWN
     speed: 0 Mbps now, 0 Mbps max
OFPT_GET_CONFIG_REPLY (xid=0x4): frags=normal miss_send_len=0

-- Rodrigo
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