#define THIS_MODULE VLM_in_band
#include "vlog.h"
+/* In-band control allows a single network to be used for OpenFlow
+ * traffic and other data traffic. Refer to ovs-vswitchd.conf(5) and
+ * secchan(8) for a description of configuring in-band control.
+ *
+ * This comment is an attempt to describe how in-band control works at a
+ * wire- and implementation-level. Correctly implementing in-band
+ * control has proven difficult due to its many subtleties, and has thus
+ * gone through many iterations. Please read through and understand the
+ * reasoning behind the chosen rules before making modifications.
+ *
+ * In Open vSwitch, in-band control is implemented as "hidden" flows (in
+ * that they are not visible through OpenFlow) and at a higher priority
+ * than wildcarded flows can be setup by the controller. This is done
+ * so that the controller cannot interfere with them and possibly break
+ * connectivity with its switches. It is possible to see all flows,
+ * including in-band ones, with the ovs-appctl "bridge/dump-flows"
+ * command.
+ *
+ * The following rules are always enabled with the "normal" action by a
+ * switch with in-band control:
+ *
+ * a. DHCP requests sent from the local port.
+ * b. ARP replies to the local port's MAC address.
+ * c. ARP requests from the local port's MAC address.
+ * d. ARP replies to the remote side's MAC address. Note that the
+ * remote side is either the controller or the gateway to reach
+ * the controller.
+ * e. ARP requests from the remote side's MAC address. Note that
+ * like (d), the MAC is either for the controller or gateway.
+ * f. ARP replies containing the controller's IP address as a target.
+ * g. ARP requests containing the controller's IP address as a source.
+ * h. OpenFlow (6633/tcp) traffic to the controller's IP.
+ * i. OpenFlow (6633/tcp) traffic from the controller's IP.
+ *
+ * The goal of these rules is to be as narrow as possible to allow a
+ * switch to join a network and be able to communicate with a
+ * controller. As mentioned earlier, these rules have higher priority
+ * than the controller's rules, so if they are too broad, they may
+ * prevent the controller from implementing its policy. As such,
+ * in-band actively monitors some aspects of flow and packet processing
+ * so that the rules can be made more precise.
+ *
+ * In-band control monitors attempts to add flows into the datapath that
+ * could interfere with its duties. The datapath only allows exact
+ * match entries, so in-band control is able to be very precise about
+ * the flows it prevents. Flows that miss in the datapath are sent to
+ * userspace to be processed, so preventing these flows from being
+ * cached in the "fast path" does not affect correctness. The only type
+ * of flow that is currently prevented is one that would prevent DHCP
+ * replies from being seen by the local port. For example, a rule that
+ * forwarded all DHCP traffic to the controller would not be allowed,
+ * but one that forwarded to all ports (including the local port) would.
+ *
+ * As mentioned earlier, packets that miss in the datapath are sent to
+ * the userspace for processing. The userspace has its own flow table,
+ * the "classifier", so in-band checks whether any special processing
+ * is needed before the classifier is consulted. If a packet is a DHCP
+ * response to a request from the local port, the packet is forwarded to
+ * the local port, regardless of the flow table. Note that this requires
+ * L7 processing of DHCP replies to determine whether the 'chaddr' field
+ * matches the MAC address of the local port.
+ *
+ * It is interesting to note that for an L3-based in-band control
+ * mechanism, the majority of rules are devoted to ARP traffic. At first
+ * glance, some of these rules appear redundant. However, each serves an
+ * important role. First, in order to determine the MAC address of the
+ * remote side (controller or gateway) for other ARP rules, we must allow
+ * ARP traffic for our local port with rules (b) and (c). If we are
+ * between a switch and its connection to the controller, we have to
+ * allow the other switch's ARP traffic to through. This is done with
+ * rules (d) and (e), since we do not know the addresses of the other
+ * switches a priori, but do know the controller's or gateway's. Finally,
+ * if the controller is running in a local guest VM that is not reached
+ * through the local port, the switch that is connected to the VM must
+ * allow ARP traffic based on the controller's IP address, since it will
+ * not know the MAC address of the local port that is sending the traffic
+ * or the MAC address of the controller in the guest VM.
+ *
+ * With a few notable exceptions below, in-band should work in most
+ * network setups. The following are considered "supported' in the
+ * current implementation:
+ *
+ * - Locally Connected. The switch and controller are on the same
+ * subnet. This uses rules (a), (b), (c), (h), and (i).
+ *
+ * - Reached through Gateway. The switch and controller are on
+ * different subnets and must go through a gateway. This uses
+ * rules (a), (b), (c), (h), and (i).
+ *
+ * - Between Switch and Controller. This switch is between another
+ * switch and the controller, and we want to allow the other
+ * switch's traffic through. This uses rules (d), (e), (h), and
+ * (i). It uses (b) and (c) indirectly in order to know the MAC
+ * address for rules (d) and (e). Note that DHCP for the other
+ * switch will not work unless the controller explicitly lets this
+ * switch pass the traffic.
+ *
+ * - Between Switch and Gateway. This switch is between another
+ * switch and the gateway, and we want to allow the other switch's
+ * traffic through. This uses the same rules and logic as the
+ * "Between Switch and Controller" configuration described earlier.
+ *
+ * - Controller on Local VM. The controller is a guest VM on the
+ * system running in-band control. This uses rules (a), (b), (c),
+ * (h), and (i).
+ *
+ * - Controller on Local VM with Different Networks. The controller
+ * is a guest VM on the system running in-band control, but the
+ * local port is not used to connect to the controller. For
+ * example, an IP address is configured on eth0 of the switch. The
+ * controller's VM is connected through eth1 of the switch, but an
+ * IP address has not been configured for that port on the switch.
+ * As such, the switch will use eth0 to connect to the controller,
+ * and eth1's rules about the local port will not work. In the
+ * example, the switch attached to eth0 would use rules (a), (b),
+ * (c), (h), and (i) on eth0. The switch attached to eth1 would use
+ * rules (f), (g), (h), and (i).
+ *
+ * The following are explicitly *not* supported by in-band control:
+ *
+ * - Specify Controller by Name. Currently, the controller must be
+ * identified by IP address. A naive approach would be to permit
+ * all DNS traffic. Unfortunately, this would prevent the
+ * controller from defining any policy over DNS. Since switches
+ * that are located behind us need to connect to the controller,
+ * in-band cannot simply add a rule that allows DNS traffic from
+ * the local port. The "correct" way to support this is to parse
+ * DNS requests to allow all traffic related to a request for the
+ * controller's name through. Due to the potential security
+ * problems and amount of processing, we decided to hold off for
+ * the time-being.
+ *
+ * - Multiple Controllers. There is nothing intrinsic in the high-
+ * level design that prevents using multiple (known) controllers,
+ * however, the current implementation's data structures assume
+ * only one.
+ *
+ * - Differing Controllers for Switches. All switches must know
+ * the L3 addresses for all the controllers that other switches
+ * may use, since rules need to be setup to allow traffic related
+ * to those controllers through. See rules (f), (g), (h), and (i).
+ *
+ * - Differing Routes for Switches. In order for the switch to
+ * allow other switches to connect to a controller through a
+ * gateway, it allows the gateway's traffic through with rules (d)
+ * and (e). If the routes to the controller differ for the two
+ * switches, we will not know the MAC address of the alternate
+ * gateway.
+ */
+
#define IB_BASE_PRIORITY 18181800
enum {
- IBR_FROM_LOCAL_DHCP, /* From local port, DHCP. */
- IBR_TO_LOCAL_ARP, /* To local port, ARP. */
- IBR_FROM_LOCAL_ARP, /* From local port, ARP. */
- IBR_TO_REMOTE_ARP, /* To remote MAC, ARP. */
- IBR_FROM_REMOTE_ARP, /* From remote MAC, ARP. */
- IBR_TO_CTL_ARP, /* To controller IP, ARP. */
- IBR_FROM_CTL_ARP, /* From controller IP, ARP. */
- IBR_TO_CTL_OFP, /* To controller, OpenFlow port. */
- IBR_FROM_CTL_OFP, /* From controller, OpenFlow port. */
+ IBR_FROM_LOCAL_DHCP, /* (a) From local port, DHCP. */
+ IBR_TO_LOCAL_ARP, /* (b) To local port, ARP. */
+ IBR_FROM_LOCAL_ARP, /* (c) From local port, ARP. */
+ IBR_TO_REMOTE_ARP, /* (d) To remote MAC, ARP. */
+ IBR_FROM_REMOTE_ARP, /* (e) From remote MAC, ARP. */
+ IBR_TO_CTL_ARP, /* (f) To controller IP, ARP. */
+ IBR_FROM_CTL_ARP, /* (g) From controller IP, ARP. */
+ IBR_TO_CTL_OFP, /* (h) To controller, OpenFlow port. */
+ IBR_FROM_CTL_OFP, /* (i) From controller, OpenFlow port. */
#if OFP_TCP_PORT != OFP_SSL_PORT
#error Need to support separate TCP and SSL flows.
#endif
projects / openvswitch / commitdiff