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73 lines
3.4 KiB
Plaintext
73 lines
3.4 KiB
Plaintext
Using LISP tunneling
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====================
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LISP is a layer 3 tunneling mechanism, meaning that encapsulated packets do
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not carry Ethernet headers, and ARP requests shouldn't be sent over the
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tunnel. Because of this, there are some additional steps required for setting
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up LISP tunnels in Open vSwitch, until support for L3 tunnels will improve.
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This guide assumes tunneling between two VMs connected to OVS bridges on
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different hypervisors reachable over IPv4. Of course, more than one VM may be
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connected to any of the hypervisors, and a hypervisor may communicate with
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several different hypervisors over the same lisp tunneling interface. A LISP
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"map-cache" can be implemented using flows, see example at the bottom of this
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file.
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There are several scenarios:
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1) the VMs have IP addresses in the same subnet and the hypervisors are also
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in a single subnet (although one different from the VM's);
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2) the VMs have IP addresses in the same subnet but the hypervisors are
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separated by a router;
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3) the VMs are in different subnets.
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In cases 1) and 3) ARP resolution can work as normal: ARP traffic is
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configured not to go through the LISP tunnel. For case 1) ARP is able to
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reach the other VM, if both OVS instances default to MAC address learning.
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Case 3) requires the hypervisor be configured as the default router for the
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VMs.
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In case 2) the VMs expect ARP replies from each other, but this is not
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possible over a layer 3 tunnel. One solution is to have static MAC address
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entries preconfigured on the VMs (e.g., `arp -f /etc/ethers` on startup on
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Unix based VMs), or have the hypervisor do proxy ARP.
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On the receiving side, the packet arrives without the original MAC header.
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The LISP tunneling code attaches a header with harcoded source and destination
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MAC address 02:00:00:00:00:00. This address has all bits set to 0, except the
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locally administered bit, in order to avoid potential collisions with existing
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allocations. In order for packets to reach their intended destination, the
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destination MAC address needs to be rewritten. This can be done using the
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flow table.
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See below for an example setup, and the associated flow rules to enable LISP
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tunneling.
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+---+ +---+
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|VM1| |VM2|
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+---+ +---+
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+--[tap0]--+ +--[tap0]---+
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[lisp0] OVS1 [eth0]-----------------[eth0] OVS2 [lisp0]
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+----------+ +-----------+
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On each hypervisor, interfaces tap0, eth0, and lisp0 are added to a single
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bridge instance, and become numbered 1, 2, and 3 respectively:
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ovs-vsctl add-br br0
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ovs-vsctl add-port br0 tap0
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ovs-vsctl add-port br0 eth0
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ovs-vsctl add-port br0 lisp0 -- set Interface lisp0 type=lisp options:remote_ip=flow options:key=flow
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Flows on br0 are configured as follows:
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priority=3,dl_dst=02:00:00:00:00:00,action=mod_dl_dst:<VMx_MAC>,output:1
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priority=2,in_port=1,dl_type=0x0806,action=NORMAL
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priority=1,in_port=1,dl_type=0x0800,vlan_tci=0,nw_src=<EID_prefix>,action=set_field:<OVSx_IP>->tun_dst,output:3
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priority=0,action=NORMAL
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Optionally, if you want to use Instance ID in a flow, you can set it with
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"action=set_tunnel:<IID>".
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