Internet Engineering Task Force (IETF) D. Saucez Request for Comments: 7835 INRIA Category: Informational L. Iannone ISSN: 2070-1721 Telecom ParisTech O. Bonaventure Universite catholique de Louvain April 2016
This document provides a threat analysis of the Locator/ID Separation Protocol (LISP).
Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
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The Locator/ID Separation Protocol (LISP) is specified in [RFC6830]. This document provides an assessment of the potential security threats for the current LISP specifications if LISP is deployed in the Internet (i.e., a public non-trustable environment).
The document is composed of three main parts. The first part defines a general threat model that attackers use to mount attacks. The second part, using this threat model, describes the techniques based on LISP and its architecture that attackers may use to construct attacks. The third part discusses mitigation techniques and general solutions to protect LISP and its architecture from attacks.
This document does not consider all the possible uses of LISP as discussed in [RFC6830] and [RFC7215] and does not cover threats due to specific implementations. The document focuses on LISP unicast, including as well LISP Interworking [RFC6832], LISP Map-Server [RFC6833], and LISP Map-Versioning [RFC6834]. Additional threats may be discovered in the future while deployment continues. The reader is assumed to be familiar with these documents for understanding the present document.
This document assumes a generic IP service and does not discuss the difference, from a security viewpoint, between using IPv4 or IPv6.
This document assumes that attackers can be located anywhere in the Internet (either in LISP sites or outside LISP sites) and that attacks can be mounted either by a single attacker or by the collusion of several attackers.
An attacker is a malicious entity that performs the action of attacking a target in a network where LISP is (partially) deployed by leveraging LISP and/or its architecture.
An attack is the action of performing an illegitimate action on a target in a network where LISP is (partially) deployed.
The target of an attack is the entity (i.e., a device connected to the network or a network) that is aimed to undergo the consequences of an attack. Other entities can potentially undergo side effects of an attack, even though they are not directly targeted by the attack. The target of an attack can be selected specifically, i.e., a particular entity, or arbitrarily, i.e., any entity. Finally, an attacker can aim to attack one or several targets with a single attack.
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Section 2.1 specifies the different modes of operation that attackers can follow to mount attacks, and Section 2.2 specifies the different categories of attacks that attackers can build.
In this document, attackers are classified according to their modes of operation, i.e., the temporal and spacial diversity of the attacker. These modes are not mutually exclusive; they can be used by attackers in any combination, and other modes may be discovered in the future. Further, attackers are not at all bound by our classification scheme, so implementers and those deploying will always need to do additional risk analysis for themselves.
On-path attackers, also known as Men-in-the-Middle, are able to intercept and modify packets between legitimate communicating entities. On-path attackers are located either directly on the normal communication path (either by gaining access to a node on the path or by placing themselves directly on the path) or outside the location path but manage to deviate (or gain a copy of) packets sent between the communication entities. On-path attackers hence mount their attacks by modifying packets initially sent legitimately between communication entities.
An attacker is called an off-path attacker if it does not have access to packets exchanged during the communication or if there is no communication. In order for their attacks to succeed, off-path attackers must hence generate packets and inject them in the network.
An internal attacker launches its attack from a node located within a legitimate LISP site. Such an attacker is either a legitimate node of the site or it exploits a vulnerability to gain access to a legitimate node in the site. Because of their location, internal attackers are trusted by the site they are in.
On the contrary, an external attacker launches its attacks from the outside of a legitimate LISP site.
A live attacker mounts attacks for which it must remain connected as long as the attack is mounted. In other words, the attacker must remain active for the whole duration of the attack. Consequently, the attack ends as soon as the attacker (or the used attack vector) is neutralized.
On the contrary, a time-shifted attacker mounts attacks that remain active after it disconnects from the Internet.
A control-plane attacker mounts its attack by using control-plane functionalities, typically the mapping system.
A data-plane attacker mounts its attack by using data-plane functionalities.
As there is no complete isolation between the control plane and the data plane, an attacker can operate in the control plane (or data plane) to mount attacks targeting the data plane (or control plane) or keep the attacked and targeted planes at the same layer (i.e., from control plane to control plane or from data plane to data plane).
The modes of operation used by attackers are not mutually exclusive; hence, attackers can combine them to mount attacks.
For example, an attacker can launch an attack using the control plane directly from within a LISP site to which it is able to get temporary access (i.e., internal + control-plane attacker) to create a vulnerability on its target and later on (i.e., time-shifted + external attacker) mount an attack on the data plane (i.e., data- plane attacker) that leverages the vulnerability.
A packet manipulation attack happens when an attacker receives a packet, modifies the packet (i.e., changes some information contained in the packet), and finally transmits the packet to its final destination, which can be the initial destination of the packet or a different one.
With a spoofing attack, the attacker injects packets in the network pretending to be another node. Spoofing attacks are made by forging source addresses in packets.
It should be noted that with LISP, packet spoofing is similar to spoofing with any other existing tunneling technology currently deployed in the Internet. Generally, the term "spoofed packet" indicates a packet containing a source IP address that is not the actual originator of the packet. Hence, since LISP uses encapsulation, the spoofed address could be in the outer header as well as in the inner header; this translates to two types of spoofing.
Inner address spoofing: The attacker uses encapsulation and uses a spoofed source address in the inner packet. In case of data-plane LISP encapsulation, that corresponds to spoofing the source Endpoint Identifier (EID) address of the encapsulated packet.
Outer address spoofing: The attacker does not use encapsulation and spoofs the source address of the packet. In case of data-plane LISP encapsulation, that corresponds to spoofing the source Routing Locator (RLOC) address of the encapsulated packet.
Note that the two types of spoofing are not mutually exclusive; rather, all combinations are possible and could be used to perform different kinds of attacks. For example, an attacker outside a LISP site can generate a packet with a forged source IP address (i.e., outer address spoofing) and forward it to a LISP destination. The packet is then eventually encapsulated by a Proxy Ingress Tunnel Router (PITR) so that once encapsulated, the attack corresponds to an inner address spoofing. One can also imagine an attacker forging a
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packet with encapsulation where both inner and outer source addresses are spoofed.
It is important to note that the combination of inner and outer spoofing makes the identification of the attacker complex as the packet may not contain information that allows detection of the origin of the attack.
In an intrusion attack, the attacker gains remote access to a resource (e.g., a host, a router, or a network) or information that it legitimately should not have accessed. Intrusion attacks can lead to privacy leakages.
In an amplification attack, the traffic generated by the target of the attack in response to the attack is larger than the traffic that the attacker must generate.
In some cases, the data plane can be several orders of magnitude faster than the control plane at processing packets. This difference can be exploited to overload the control plane via the data plane without overloading the data plane.
To reduce the time required to obtain a mapping, the optional gleaning mechanism defined for LISP allows an xTR (Ingress and/or Egress Tunnel Router) to directly learn a mapping from the LISP- encapsulated data packets and the Map-Request packets that it receives. LISP-encapsulated data packets contain a source RLOC, destination RLOC, source EID, and destination EID. When an xTR receives an encapsulated data packet coming from a source EID for which it does not already know a mapping, it may insert the mapping between the source RLOC and the source EID in its EID-to-RLOC cache. The same technique can be used when an xTR receives a Map-Request as the Map-Request also contains a source EID address and a source RLOC. Once a gleaned entry has been added to the EID-to-RLOC cache, the xTR sends a Map-Request to retrieve the actual mapping for the gleaned EID from the mapping system.
If a packet injected by an off-path attacker and with a spoofed inner address is gleaned by an xTR, then the attacker may divert the traffic meant to be delivered to the spoofed EID as long as the gleaned entry is used by the xTR. This attack can be used as part of replay, packet manipulation, packet interception and suppression, or DoS attacks as the packets are sent to the attacker.
If the packet sent by the attacker contains a spoofed outer address instead of a spoofed inner address, then it can achieve a DoS or a performance attack as the traffic normally destined to the attacker will be redirected to the spoofed source RLOC. Such traffic may overload the owner of the spoofed source RLOC, preventing it from operating properly.
If the packet injected uses both inner and outer spoofing, the attacker can achieve a spoofing, a performance, or an amplification attack as traffic normally destined to the spoofed EID address will
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be sent to the spoofed RLOC address. If the attacked LISP site also generates traffic to the spoofed EID address, such traffic may have a positive amplification factor.
A gleaning attack does not only impact the data plane but can also have repercussions on the control plane as a Map-Request is sent after the creation of a gleaned entry. The attacker can then achieve DoS and performance attacks on the control plane. For example, if an attacker sends a packet for each address of a prefix not yet cached in the EID-to-RLOC cache of an xTR, the xTR will potentially send a Map-Request for each such packet until the mapping is installed, which leads to an over-utilization of the control plane as each packet generates a control-plane event. In order for this attack to succeed, the attacker may not need to use spoofing. This issue can occur even if gleaning is turned off since whether or not gleaning is used, the ITR may need to send a Map-Request in response to incoming packets whose EID is not currently in the cache.
Gleaning attacks fundamentally involve a time-shifted mode of operation as the attack may last as long as the gleaned entry is kept by the targeted xTR. [RFC6830] recommends storing the gleaned entries for only a few seconds, which limits the duration of the attack.
Gleaning attacks always involve external data-plane attackers but result in attacks on either the control plane or data plane.
Note that the outer spoofed address does not need to be the RLOC of a LISP site; it may be any address.
When the L bit in the LISP header is set to 1, it indicates that the second 32-bit longword of the LISP header contains the Locator- Status-Bits (LSBs). In this field, each bit position reflects the status of one of the RLOCs mapped to the source EID found in the encapsulated packet. The reaction of a LISP xTR that receives such a packet is left as an operational choice in [RFC6830].
When an attacker sends a LISP-encapsulated packet with an illegitimately crafted LSB to an xTR, it can influence the xTR's choice of the locators for the prefix associated with the source EID. In case of an off-path attacker, the attacker must inject a forged packet in the network with a spoofed inner address. An on-path attacker can manipulate the LSB of legitimate packets passing through it and hence does not need to use spoofing. Instead of manipulating the LSB field, an on-path attacker can also obtain the same result of injecting packets with invalid LSB values by replaying packets.
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The LSB field can be leveraged to mount a DoS attack by either declaring all RLOCs as unreachable (all LSBs set to 0), concentrating all the traffic to one RLOC (e.g., all but one LSB set to 0), and hence overloading the RLOC concentrating all the traffic from the xTR, or by forcing packets to be sent to RLOCs that are actually not reachable (e.g., invert LSB values).
The LSB field can also be used to mount a replay, a packet manipulation, or a packet interception and suppression attack. Indeed, if the attacker manages to be on the path between the xTR and one of the RLOCs specified in the mapping, forcing packets to go via that RLOC implies that the attacker will gain access to the packets.
Attacks using the LSB fundamentally involve a time-shifted mode of operation as the attack may last as long as the reachability information gathered from the LSB is used by the xTR to decide the RLOCs to be used.
When the Map-Version bit of the LISP header is set to 1, it indicates that the low-order 24 bits of the first 32-bit longword of the LISP header contain a Source and Destination Map-Version. When a LISP xTR receives a LISP-encapsulated packet with the Map-Version bit set to 1, the following actions are taken:
o It compares the Destination Map-Version found in the header with the current version of its own configured EID-to-RLOC mapping for the destination EID found in the encapsulated packet. If the received Destination Map-Version is smaller (i.e., older) than the current version, the Egress Tunnel Router (ETR) should apply the Solicit-Map-Request (SMR) procedure described in [RFC6830] and send a Map-Request with the SMR bit set.
o If a mapping exists in the EID-to-RLOC cache for the source EID, then it compares the Map-Version of that entry with the Source Map-Version found in the header of the packet. If the stored mapping is older (i.e., the Map-Version is smaller), than the source version of the LISP-encapsulated packet, the xTR, should send a Map-Request for the source EID.
A cross-mode attacker can use the Map-Version bit to mount a DoS attack, an amplification attack, or a spoofing attack. For instance, if the mapping cached at the xTR is outdated, the xTR will send a Map-Request to retrieve the new mapping, which can yield to a DoS attack (by excess of signaling traffic) or an amplification attack if the data-plane packet sent by the attacker is smaller, or otherwise uses fewer resources, than the control-plane packets sent in response
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to the attacker's packet. With a spoofing attack, and if the xTR considers that the spoofed ITR has an outdated mapping, it will send an SMR to the spoofed ITR, which can result in a performance, amplification, or DoS attack as well.
Map-Version attackers are inherently cross-mode as the Map-Version is a method to put control information in the data plane. Moreover, this vector involves live attackers. Nevertheless, on-path attackers do not have a specific advantage over off-path attackers.
The Nonce-Present and Echo-Nonce bits in the LISP header are used to verify the reachability of an xTR. A testing xTR sets the Echo-Nonce and the Nonce-Present bits in LISP-encapsulated data packets and includes a random nonce in the LISP header of the packets. Upon reception of these packets, the tested xTR stores the nonce and echoes it whenever it returns a LISP-encapsulated data packet to the testing xTR. The reception of the echoed nonce confirms that the tested xTR is reachable.
An attacker can interfere with the reachability test by sending two different types of packets:
1. LISP-encapsulated data packets with the Nonce-Present bit set and a random nonce. Such packets are normally used in response to a reachability test.
2. LISP-encapsulated data packets with the Nonce-Present and the Echo-Nonce bits both set. These packets will force the receiving ETR to store the received nonce and echo it in the LISP- encapsulated packets that it sends. These packets are normally used as a trigger for a reachability test.
The first type of packets are used to make xTRs think that another xTR is reachable when it is not. It is hence a way to mount a DoS attack (i.e., the ITR will send its packet to a non-reachable ETR when it should use another one).
The second type of packets could be exploited to attack the nonce- based reachability test. If the attacker sends a continuous flow of packets that each have a different random nonce, the ETR that receives such packets will continuously change the nonce that it returns to the remote ITR, which can yield to a performance attack. If the remote ITR tries a nonce reachability test, this test may fail because the ETR may echo an invalid nonce. This hence yields to a DoS attack.
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In the case of an on-path attacker, a packet manipulation attack is necessary to mount the attack. To mount such an attack, an off-path attacker must mount an outer address spoofing attack.
If an xTR chooses to periodically check with active probes the liveness of entries in its EID-to-RLOC cache (as described in Section 6.3 of [RFC6830]), then this may amplify the attack that caused the insertion of entries being checked.
LISP allows a 24-bit value called Instance ID to be carried in its header; it's used on the ITR to indicate which local Instance ID has been used for encapsulation, while on the ETR, the Instance ID decides which forwarding table to use to forward the decapsulated packet in the LISP site.
An attacker (either a control-plane or data-plane attacker) can use the Instance ID functionality to mount an intrusion attack.
[RFC6832] defines Proxy-ITR and Proxy-ETR network elements to allow LISP and non-LISP sites to communicate. The Proxy-ITR has functionality similar to the ITR; however, its main purpose is to encapsulate packets arriving from the Default-Free Zone (DFZ) in order to reach LISP sites. A Proxy Egress Tunnel Router (PETR) has functionality similar to the ETR; however, its main purpose is to inject de-encapsulated packets in the DFZ in order to reach non-LISP sites from LISP sites. As a PITR (or PETR) is a particular case of ITR (or ETR), it is subject to similar attacks as ITRs (or ETRs).
As any other system relying on proxies, LISP interworking can be used by attackers to hide their exact origin in the network.
A control-plane off-path attacker can exploit Map-Request messages to mount DoS, performance, or amplification attacks. By sending Map- Request messages at a high rate, the attacker can overload nodes involved in the mapping system. For instance, sending Map-Requests at a high rate can considerably increase the state maintained in a Map-Resolver or consume CPU cycles on ETRs that have to process the Map-Request packets they receive in their slow path (i.e., performance or DoS attack). When the Map-Reply packet is larger than the Map-Request sent by the attacker, that yields to an amplification
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attack. The attacker can combine the attack with a spoofing attack to overload the node to which the spoofed address is actually attached.
Note that if the attacker sets the P bit (Probe Bit) in the Map- Request, the Map-Request will be legitimately sent directly to the ETR instead of passing through the mapping system.
The SMR bit can be used to mount a variant of these attacks.
For efficiency reasons, Map-Records can be appended to Map-Request messages. When an xTR receives a Map-Request with appended Map- Records, it does the same operations as for the other Map-Request messages and so is subject to the same attacks. However, it also installs in its EID-to-RLOC cache the Map-Records contained in the Map-Request. An attacker can then use this vector to force the installation of mappings in its target xTR. Consequently, the EID- to-RLOC cache of the xTR is polluted by potentially forged mappings allowing the attacker to mount any of the attacks categorized in Section 2.2 (see Section 3.8 for more details). Note that the attacker does not need to forge the mappings present in the Map- Request to achieve a performance or DoS attack. Indeed, if the attacker owns a large enough EID prefix, it can de-aggregate it in many small prefixes, each corresponding to another mapping, and it installs them in the xTR cache by means of the Map-Request.
Moreover, attackers can use Map Resolver and/or Map Server network elements to relay its attacks and hide the origin of the attack. Indeed, on the one hand, a Map Resolver is used to dispatch Map- Request to the mapping system, and on the other hand, a Map Server is used to dispatch Map-Requests coming from the mapping system to ETRs that are authoritative for the EID in the Map-Request.
Most of the security risks associated with Map-Reply messages will depend on the 64-bit nonce that is included in a Map-Request and returned in the Map-Reply. Given the size of the nonce (64 bits), if a best current practice is used [RFC4086] and if an ETR does not accept Map-Reply messages with an invalid nonce, the risk of an off- path attack is limited. Nevertheless, the nonce only confirms that the Map-Reply received was sent in response to a Map-Request sent; it does not validate the contents of that Map-Reply.
If an attacker manages to send a valid (i.e., in response to a Map- Request and with the correct nonce) Map-Reply to an ITR, then it can perform any of the attacks categorized in Section 2.2 as it can inject forged mappings directly in the ITR EID-to-RLOC cache. For
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instance, if the mapping injected to the ITR points to the address of a node controlled by the attacker, it can mount replay, packet manipulation, packet interception and suppression, or DoS attacks, as it will receive every packet destined to a destination lying in the EID prefix of the injected mapping. In addition, the attacker can inject a plethora of mappings in the ITR to mount a performance attack by filling up the EID-to-RLOC cache of the ITR. The attacker can also mount an amplification attack if the ITR at that time is sending a large number of packets to the EIDs matching the injected mapping. In this case, the RLOC address associated with the mapping is the address of the real target of the attacker, so all the traffic of the ITR will be sent to the target, which means that with one single packet the attacker may generate very high traffic towards its final target.
If the attacker is a valid ETR in the system, it can mount a rogue attack if it uses prefix overclaiming. In such a scenario, the attacker ETR replies to a legitimate Map-Request message that it received with a Map-Reply message that contains an EID prefix that is larger than the prefix owned by the attacker. For example, if the owned prefix is 192.0.2.0/25 but the Map-Reply contains a mapping for 192.0.2.0/24, then the mapping will influence packets destined to EIDs other than the one the attacker has authority on. With such technique, the attacker can mount the attacks presented above as it can (partially) control the mappings installed on its target ITR. To force its target ITR to send a Map-Request, nothing prevents the attacker to initiate some communication with the ITR. This method can be used by internal attackers that want to control the mappings installed in their site. To that aim, they simply have to collude with an external attacker ready to overclaim prefixes on behalf of the internal attacker.
Note that when the Map-Reply is in response to a Map-Request sent via the mapping system (i.e., not sent directly from the ITR to an ETR), the attacker does not need to use a spoofing attack to achieve its attack as by design the source IP address of a Map-Reply is not known in advance by the ITR.
Map-Request and Map-Reply messages are exposed to any type of attackers, on-path or off-path but also external or internal attackers. Also, even though they are control messages, they can be leveraged by data-plane attackers. As the decision of removing mappings is based on the TTL indicated in the mapping, time-shifted attackers can take advantage of injecting forged mappings as well.
Map-Register messages are sent by ETRs to Map Servers to indicate to the mapping system the EID prefixes associated with them. The Map- Register message provides an EID prefix and the list of ETRs that are able to provide Map-Replies for the EID covered by the EID prefix.
As Map-Register messages are protected by an authentication mechanism, only a compromised ETR can register itself to its allocated Map Server.
A compromised ETR can overclaim the prefix it owns in order to influence the route followed by Map-Requests for EIDs outside the scope of its legitimate EID prefix (see Section 3.8 for the list of overclaiming attacks).
A compromised ETR can also de-aggregate its EID prefix in order to register more EID prefixes than necessary to its Map Servers (see Section 3.7 for the impact of de-aggregation of prefixes by an attacker).
Similarly, a compromised Map Server can accept an invalid registration or advertise an invalid EID prefix to the mapping system.
Map-Notify messages are sent by a Map Server to an ETR to acknowledge the reception and processing of a Map-Register message.
Similarly, to the pair Map-Request/Map-Reply, the pair Map-Register/ Map-Notify is protected by a nonce making it difficult for an attacker to inject a falsified notification to an ETR to make this ETR believe that the registration succeeded when it has not.
As reviewed in [RFC6973], universal privacy considerations are difficult to establish as the privacy definitions may vary for different scenarios. As a consequence, this document does not aim to identify privacy issues related to the LISP protocol, but the security threats identified in this document could play a role in privacy threats as defined in Section 5 of [RFC6973].
Similar to public deployments of any other control-plane protocol, in an Internet deployment, LISP mappings are public and hence provide information about the infrastructure and reachability of LISP sites (i.e., the addresses of the edge routers). Depending upon deployment
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details, LISP map replies might or might not provide finer-grained and more detailed information than is available with currently deployed routing and control protocols.
Most of the above threats can be mitigated with careful deployment and configuration (e.g., filter) and also by applying the general rules of security, e.g., only activating features that are necessary for the deployment and verifying the validity of the information obtained from third parties.
The control plane is the most critical part of LISP from a security viewpoint, and it is worth noticing that the LISP specifications already offer an authentication mechanism for mappings registration [RFC6833]. This mechanism, combined with LISP-SEC [LISP-SEC], strongly mitigates threats in non-trustable environments such as the Internet. Moreover, an authentication data field for Map-Request messages and Encapsulated Control messages was allocated [RFC6830]. This field provides a general authentication mechanism technique for the LISP control plane that future specifications may use while staying backward compatible. The exact technique still has to be designed and defined. To maximally mitigate the threats on the mapping system, authentication must be used, whenever possible, for both Map-Request and Map-Reply messages and for messages exchanged internally among elements of the mapping system, such as specified in [LISP-SEC] and [LISP-DDT].
Systematically applying filters and rate limitation, as proposed in [RFC6830], will mitigate most of the threats presented in this document. In order to minimize the risk of overloading the control plane with actions triggered from data-plane events, such actions should be rate limited.
Moreover, all information opportunistically learned (e.g., with LSB or gleaning) should be used with care until they are verified. For example, a reachability change learned with LSB should not be used directly to decide the destination RLOC but instead should trigger a rate-limited reachability test. Similarly, a gleaned entry should be used only for the flow that triggered the gleaning procedure until the gleaned entry has been verified [Trilogy].
[Trilogy] Saucez, D. and L. Iannone, "How to mitigate the effect of scans on mapping systems", Trilogy Future Internet Summer School, 2009.
This document builds upon the document by Marcelo Bagnulo [PRELIM-LISP-THREAT], where the flooding attack and the reference environment was first described.
The authors would like to thank Ronald Bonica, Deborah Brungard, Albert Cabellos, Ross Callon, Noel Chiappa, Florin Coras, Vina Ermagan, Dino Farinacci, Stephen Farrell, Joel Halpern, Emily Hiltzik, Darrel Lewis, Edward Lopez, Fabio Maino, Terry Manderson, and Jeff Wheeler for their comments.