4 LISP is a layer 3 tunneling mechanism, meaning that encapsulated packets do
5 not carry Ethernet headers, and ARP requests shouldn't be sent over the
6 tunnel. Because of this, there are some additional steps required for setting
7 up LISP tunnels in Open vSwitch, until support for L3 tunnels will improve.
9 This guide assumes tunneling between two VMs connected to OVS bridges on
10 different hypervisors reachable over IPv4. Of course, more than one VM may be
11 connected to any of the hypervisors, and a hypervisor may communicate with
12 several different hypervisors over the same lisp tunneling interface. A LISP
13 "map-cache" can be implemented using flows, see example at the bottom of this
16 There are several scenarios:
18 1) the VMs have IP addresses in the same subnet and the hypervisors are also
19 in a single subnet (although one different from the VM's);
20 2) the VMs have IP addresses in the same subnet but the hypervisors are
21 separated by a router;
22 3) the VMs are in different subnets.
24 In cases 1) and 3) ARP resolution can work as normal: ARP traffic is
25 configured not to go through the LISP tunnel. For case 1) ARP is able to
26 reach the other VM, if both OVS instances default to MAC address learning.
27 Case 3) requires the hypervisor be configured as the default router for the
30 In case 2) the VMs expect ARP replies from each other, but this is not
31 possible over a layer 3 tunnel. One solution is to have static MAC address
32 entries preconfigured on the VMs (e.g., `arp -f /etc/ethers` on startup on
33 Unix based VMs), or have the hypervisor do proxy ARP.
35 On the receiving side, the packet arrives without the original MAC header.
36 The LISP tunneling code attaches a header with harcoded source and destination
37 MAC address 02:00:00:00:00:00. This address has all bits set to 0, except the
38 locally administered bit, in order to avoid potential collisions with existing
39 allocations. In order for packets to reach their intended destination, the
40 destination MAC address needs to be rewritten. This can be done using the
43 See below for an example setup, and the associated flow rules to enable LISP
50 +--[tap0]--+ +--[tap0]---+
52 [lisp0] OVS1 [eth0]-----------------[eth0] OVS2 [lisp0]
54 +----------+ +-----------+
56 On each hypervisor, interfaces tap0, eth0, and lisp0 are added to a single
57 bridge instance, and become numbered 1, 2, and 3 respectively:
60 ovs-vsctl add-port br0 tap0
61 ovs-vsctl add-port br0 eth0
62 ovs-vsctl add-port br0 lisp0 -- set Interface lisp0 type=lisp options:remote_ip=flow options:key=flow
64 Flows on br0 are configured as follows:
66 priority=3,dl_dst=02:00:00:00:00:00,action=mod_dl_dst:<VMx_MAC>,output:1
67 priority=2,in_port=1,dl_type=0x0806,action=NORMAL
68 priority=1,in_port=1,dl_type=0x0800,vlan_tci=0,nw_src=<EID_prefix>,action=set_field:<OVSx_IP>->tun_dst,output:3
69 priority=0,action=NORMAL
71 Optionally, if you want to use Instance ID in a flow, you can set it with
72 "action=set_tunnel:<IID>".