The Story Continues – Another IPv6 Update

TROOPERS12 came to an end last week on Friday; needless to say it was an awesome  event. 😉
The first two days offered workshops on various topics. On Monday Enno, Marc “Van Hauser” Heuse and I gave a one day workshop on “Advanced IPv6 Security”.  I think attendees as well as trainers had a real good time during and after the workshop fiddling around with IPv6. Especially Marc had quite some fun as he discovered that we provided “global” IPv6 Connectivity for the conference network, and according to one of his tweets, TROOPERS12 was the first security conference he visited, offering this kind of connectivity.

So back to the topic

Our last posts on IPv6 Security go back to the first half of 2011. If you haven’t read them already, now it’s a good time to do so. You can find them here, here, here and here.

In the last post of the series Enno discussed how RA-Guard can be circumvented with clever use of extension headers. As a short reminder, the packet dump looks like this.

The Information of the upper-layer protocol is only present in the second fragment, so RA Guard does not kick in.

As we found out on the Heise IPv6 Kongress last year, this issue can be mitigated with the following parameter in an IPv6 ACL.

deny ipv6 any any undetermined-transport

As a reminder, this parameter drops all IPv6 packets where the upper-layer protocol information cannot be determined.

After the workshop was officially over, Marc and I played a little bit with this ACL Parameter to see if it is working as intended. So I configured the following IPv6 ACL on our beautiful Cisco 4948E:

4948E(config)#ipv6 access-list IPv6
4948E(config-ipv6-acl)#deny ipv6 any any undetermined-transport
4948E(config-ipv6-acl)#permit ipv6 any any
4948E(config)#interface g1/19
4948E(config-if)#ipv6 traffic-filter IPv6 in

We started the attack again with the following parameter:

Apparently nothing happened with my (IPv6 enabled) laptop (which is a good thing ;))

The corresponding packet dump looked quite unspectacular:

Only the STP packets could be seen, and the flooded router advertisements were dropped by the Switch.

So could this parameter solve the issue with the whole RA mess?

Unfortunately the answer is no. The ACL parameter does mitigate the issue with the fragmented router advertisement. However, the ACL parameter can be circumvented by using overlapping fragments. Unfortunately we couldn’t test this scenario because this wasn’t yet implemented in the THC Tool Suite, but this is just a matter of time…

The IPv6 Packet  basically looks like this:

Fragment 1:
IPv6 Header
Fragmentation Header
Destination Header (8 bytes)
ICMPv6 with Echo Request
Fragment 2:
IPv6 Header
Fragmentation Header with offset == 1 (equals position of 8th byte ==
start of Echo Request in first fragment)
ICMPv6 with RA


In this case it depends on the operating system whether or not the packet is discarded when overlapping fragments are detected. RFC 5722 is very specific on how these should be handled:

“When reassembling an IPv6 datagram, if one or more its
constituent fragments is determined to be an overlapping
fragment,the entire datagram (and any constituent fragments,
including those not yet received) MUST be silently discarded.”

So it is up to the operating system to implement this behavior. We’ll see how things work out 😉

If you’re interested in more IPv6 issues, or simply wanna chat about this topic, meet Enno and me again at the  Heise IPv6 Kongress this year in Frankfurt, where we will give a talk on IPv6 as well.

Have great day,


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A Comment on Android PIN bypass

Lately there have been some rumors on the full-disclosure mailing list referring to a blogpost of  Hatforce about a new method to bypass the PIN/password lock on Android Gingerbread phones.
The approach was to boot into the Recovery Mode and execute a reset to factory state. The ideal result should be a reliable wipe of the /data partition. However, the author managed to recover data after the wiping process. This has been stated as a method on extracting sensitive date without knowing the actual pin or passcode.

This approach was tested on a Nexus S smartphone with Android 2.3.6 assuming the problem could be present on other devices too.
As of our experience this actually affects all Android devices without device encryption. Meanwhile we had more than ten different Android 2.3.x devices from four different vendors. All of them need less than a minute for a factory reset. An actual example is the HTC Desire HD with a  1,1GB /data partition excluding the /cache partition. The factory reset procedure took about  40 seconds, which can hold as an advice to question if this time is actually sufficient to wipe the whole storage. Finally we have been able to recover data after factory-reset devices as part of previous studies.

Besides mentioning that the source code indicates Android devices runnig Android Honeycomb and later effectively wipe data. After looking up in the source code of Android Ice Cream Sandwich we found that the FileWriter class is used for the wipe of the /cache and /data partition. So no indication on overwriting the data here. We assume, that by mentioning the issue as resolved, he was referring to Android Honeycomb device encryption being use, which indeed resolves this issue. This feature has been announced as a new feature anyway.

The fact about getting the data without knowing the PIN however does not really fit the case. From our opinion that’s not a new thought anyway. As long as the storage is not encrypted there always ways to access and read it. My favorite way is to flash the recovery mode with a custom one, e.g. ClockWorkMod By this means it’s possible to run Android Debugging Bridge, su and dd binaries which in return can be used to connect to the device via USB cable and create a raw copy of the storage. Additionally it becomes available to follow the loudness principle and acquire data on a forensic level.

However there is one important aspect mentioned in the blogpost, which we fully agree with: lost device means lost data!

Have a great day



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Troopers TelcoSecDay

As there has been some public demand for that, here we go with the final agenda for the Troopers “TelcoSecDay“. The workshop is meant to provide a platform for research exchange between operators, vendors and researchers. The slides of the talks will potentially be made available as well.

  • 8:30: Opening Remarks & Introduction
  • 9:00: Sebastian Schrittwieser (SBA Research): Guess Who’s Texting You? Evaluating the Security of Smartphone Messaging Applications.
  • 10:00: Peter Schneider (NSN): How to secure an LTE-Network: Just applying the 3GPP security standards and that’s it?
  • 10:45: Break
  • 11:00: Kevin Redon (T-Labs): Weaponizing Femtocells – The Effect of Rogue Devices on Mobile Telecommunications
  • 11:45: Christian Kagerhuber (Group IT Security, Deutsche Telekom AG): Security Compliance Audit Automation (SCA, TeleManagementForum TMF528)
  • 12:30: Lunch
  • 13:45: Philipp Langlois (P1 Security): Assault on the GRX (GPRS Roaming eXchange) from the Telecom Core Network perspective, from 2.5G to LTE Advanced.
  • 15:00: Break
  • 15:15: Harald Welte (sysmocom): Structural deficits in telecom security
  • 16:30: Closing Remarks
  • 17:00: End of workshop
  • 19:00: Joint dinner (hosted by ERNW) in Heidelberg Altstadt for those interested and/or staying for the main conference


Synopses & Bios

Sebastian Schrittwieser: Guess Who’s Texting You? Evaluating the Security of Smartphone Messaging Applications.

Synopsis: Recently, a new generation of Internet-based messaging applications for smartphones was introduced. While user numbers are estimated in the millions, little attention has so far been paid to the security of these applications. In this talk, we present our experimental results, which revealed major security flaws, allowing attackers to hijack accounts, spoof sender-IDs, and enumerate subscribers.

Bio: Sebastian Schrittwieser is a PhD candidate at the Vienna University of Technology and a researcher at SBA Research. His research interests include, among others, digital forensics, software protection, code obfuscation, and digital fingerprinting. Sebastian received a Dipl.-Ing. (equivalent to MSc) degree in Business Informatics with focus on IT security from the Vienna University of Technology in 2010.


Peter Schneider: How to secure an LTE-Network: Just applying the 3GPP security standards and that’s it?

Synopsis: This talk briefly introduces the security architecture of an LTE mobile network as specified by 3GPP and shows which threats it mitigates and which not. It discusses additional, not-standardized security measures and how they can contribute to making mobile networks as secure as they need to be.

Bio: After many years of research, prototyping and systems engineering in the area of communication technologies, Peter works currently as a senior expert for mobile network security in the Security Technologies Team at Nokia Siemens Networks Research. He is author of various mobile network related security concepts. He is also active in the 3GPP security standardization and in several security research projects.


Kevin Redon: Weaponizing Femtocells – The Effect of Rogue Devices on Mobile Telecommunications

Synopsis: Mobile phones and carriers trust the traditional base stations which serve as the interface between the mobile devices and the fixed-line communication network. Femtocells, miniature cellular base stations installed in homes and businesses, are equally trusted yet are placed in possibly untrustworthy hands. By making several modifications to a commercially available femtocell, we evaluate the impact of attacks originating from a compromised device. We show that such a rogue device can violate all the important aspects of security for mobile subscribers, including tracking phones, intercepting communication and even modifying and impersonating traffic. The specification also enables femtocells to directly communicate with other femtocells over a VPN and the carrier we examined had no filtering on such communication, enabling a single rogue femtocell to directly communicate with (and thus potentially attack) all other femtocells within the carrier’s network.

Bio: Kevin Redon does his master of computing at the Technische Universitaet Berlin. He also works for “Security in Telecommunication” (SecT), a research group of the university.


Christian Kagerhuber: Security Compliance Audit Automation (SCA, TeleManagementForum TMF528)

Synopsis: Today, Service Providers are in need of comprehensive information relevant to effective security management. Service Providers have to evaluate and verify the compliance of their infrastructure and services to corporate security  directives and legal guidelines. This includes being able to retrace OSS Operators’ behavior on OSS systems via standardized log messages. But to answer all necessary security compliance questions, log data alone appears not to be sufficient.
Service Providers need configuration data and telemetry data centralized at hand without manual, time-consuming OSS Operator activity. Even interactive polling of their devices is not sufficient because Service Providers must track down changes in the environment and the effective date/period. The talk is about what to solve this problem.

Bio: Christian is a Senior Security Expert at Deutsche Telekom (DT), responsible for the security of DT’s NGOSS system (called NGSSM) and BNG/SCRAT project. He build up T-Online’s Identity Management and CERT and is the author of various Deutsche Telekom security standards, e.g. on platform virtualisation and SSH.


Philippe Langlois: Assault on the GRX (GPRS Roaming eXchange) from the Telecom Core Network perspective, from 2.5G to LTE Advanced.

Synopsis: GRX is the global private network where Telecom network operators exchange GPRS roaming traffic of their users. It’s also used for all M2M networks where roaming is used, and that is the case from some company’s truck fleet management system down to intelligence GPS location spybug tracking system. GPRS has been there from 2.5G GSM networks to the upcoming LTE Advanced networks, and is now quite widespread technology, along with its attacks. GRX has had a structuring role in the global telecom world at a time where IP dominance was being to be acknowledged. Now it has expanded to a lightweight structure using both IP technologies and ITU-originated protocols.
We’ll see how this infrastructure is protected and can be attacked, and we’ll discover the issues with the specific telco equipment inside GRX, namely GGSN and SGSN but also now PDN Gateways in LTE and LTE Advanced “Evolved Packet Core”. We will see its implication with GTP protocol, DNS infrastructure, AAA servers and core network technologies such as MPLS, IPsec VPNs and their associated routing protocols. These network elements were rarely evaluated for security, and during our engagements with vulnerability analysis, we’ve seen several typical vulnerabilities that we will be showed in this speech. We will demo some of the attacks on a simulated “PS Domain” network, that it the IP part of the Telecom Core Network that transports customers’ traffic, and investigate its relationships with legacy SS7, SIGTRAN IP backbones, M2M private corporate VPNs and telecom billing systems. We will also seem how automation enable us to succeed at attacks which are hard to perform and will show how a “sentinel” attack was able to compromise a telecom Core Network during one penetration test.

Bio: Philippe Langlois is a leading security researcher and expert in the domain of telecom and network security. He founded internationally recognized security companies (Qualys, WaveSecurity, INTRINsec, P1 Security) as well as led technical, development and research teams (Solsoft, TSTF). He founded Qualys and led the world-leading vulnerability assessment service. He founded a pioneering network security company Intrinsec in 1995 in France. His founded his first business, Worldnet, France’s first public Internet service provider, in 1993. Philippe was also lead designer for Payline, one of the first e-commerce payment gateways. He has written and translated security books, including some of the earliest references in the field of computer security, and has been giving speeches on network security since 1995 (Interop, BlackHat, HITB, Previously professor at Ecole de Guerre Economique and various universities in France (Amiens, Marne La Vallée) and internationally (FUSR-U, EERCI). He is a FUSR-U (Free University for Security Research) collaborator and founding member. Philippe is providing industry associations (GSM Association Security Group, several national organizations) and governmental officials with Critical Infrastructure advisory conferences in Telecom and Network security. Now Philippe is providing with P1 Security the first Core Network Telecom Signaling security scanner & auditor which help telecom companies, operator and government analyze where and how their critical telecom network infrastructure can be attacked. He can be reached through his website at:
He has presented previously at these security/hacking conferences:, Hack in the Box (HITB), Blackhat, Hackito Ergo Sum (paris, France), SOURCE, Chaos Communication Congress (Berlin, Germany), ekoparty (bueos aires, argentina), H2HC (sao paulo, brazil), SYSCAN (Hong Kong; Thailand), Bellua (Jakarta, Indonesia), INT (Mauritius), Interop… (some events listed there )


Harald Welte: Structural deficits in telecom security

Synopsis: Especially in recent years, numerous practical attacks and tools have been developed and released.  The attack patterns and methods from the dynamic Internet world have finally caught up with the dinosaur of the Telecom world.  So far, the industry has failed to demonstrate sufficient interest in developing proper responses.  The changes so far have been superficial.  Are they a sufficient response for what is to come?  Has the telecom industry realized the true implications of having left the “walled garden”?  The talk will leave the field of actual attacks behind in order to talk about what at least the author perceives as structural deficits in terms of IT security at operators and equipment vendors.

Bio: Harald Welte is communications security consultalt for more than a decade. He was co-author of tne netfilter/iptables packet filter in the Linux kernel and has since then been involved in a variety of Free Software based implementations of protocol stacks for RFID, GSM, GPRS, and TETRA.  His main interest is to look at security of communication systems beyond the IP-centric mainstream.  Besides his consulting work, he is the general manager of Sysmocom GmbH, providing custom tailored communications solutions to customers world-wide.


Have a great Sunday everybody, see you soon at Troopers 😉


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ERP Platforms Are Vulnerable

This is a guest post by the SAP security expert Juan Pablo Perez-Etchegoyen, CTO of  Onapsis. Enjoy reading:

At Onapsis we are continuously researching in the ERP security field to identify the risks that ERP systems and business-critical applications are exposed to. This way we help customers and vendors to increase their security posture and mitigate threats that may be affecting their most important platform: the one that stores and manages their business’ crown jewels.

We have been talking about SAP security in many conferences over the last years, not only showing how to detect insecure settings and vulnerabilities but also explaining how to mitigate and solve them.  However, something that is still less known is that since 2009 we have been also doing research over Oracle’s ERP systems (JD Edwards, Siebel, PeopleSoft, E-Business Suite) and reporting vulnerabilities to the vendor. In this post, I’m going to discuss some of the vulnerabilities that we reported, Oracle fixed and released patches in the latest CPU (Critical Patch Update) of January 2012. In this CPU, 8 vulnerabilities reported by Onapsis affecting JD Edwards were fixed.

What’s really important about these vulnerabilities is that most of them are highly critical, enabling a remote unauthenticated attacker to fully compromise the ERP server just having network access to it.  I’m going to analyze some these vulnerabilities to shed some light on the real status of JD Edwards’ security. Most of these vulnerabilities are exploitable through the JDENET service, which is a proprietary protocol used by JDE for connecting the different servers.

Let’s take a look at the most interesting issues:

ONAPSIS-2012-001: Oracle JD Edwards JDENET Arbitrary File Write

Sending a specific packet in the JDENET message, an attacker can basically instruct the server to write an arbitrary content in an arbitrary location, leading to an arbitrary file write condition.

ONAPSIS-2012-002: Oracle JD Edwards Security Kernel Remote Password Disclosure

Sending a packet containing key hard-coded in the kernel, an attacker can “ask for” a user’s password (!)

ONAPSIS-2012-003: Oracle JD Edwards SawKernel Arbitrary File Read

An attacker can read any file, by connecting to the JDENET service.

ONAPSIS-2012-007: Oracle JD Edwards SawKernel SET_INI Configuration Modification Modifications to the server configuration (JDE.INI) can be performed remotely and without authentication. Several attacks are possible abusing this vulnerability.

ONAPSIS-2012-006: Oracle JD Edwards JDENET Large Packets Denial of Service

If an attacker sends packets larger than a specific size, then the server’s CPU start processing at 100% of its capacity. Game over.

As a “bonus” to this guest blog post, I would like to analyze a vulnerability related to the set of  security advisories we released back on April 2011 (many of them also critical). This vulnerability is the ONAPSIS-2011-07.

The exploitation of this weakness is very straight-forward, as the only thing an attacker needs to do is to send a packet to the JDENET command service (typically UDP port 6015) with the message “SHUTDOWN”, and all JD Edwards services are powered off! Business impact? None of the hundreds/thousands of the company’s employees that need the ERP system to do their every-day work will be able to do their job.

Some people still talk about ERP security as a synonym of Segregation of Duties controls. This is just an example of a high-impact Denial of Service attack that can be performed against the technical components of these systems. No user or password. No roles or authorizations.

Even worse, as UDP connections are stateless, it’s trivial for the attacker to forge its source and exploit the vulnerability potentially bypassing firewall filters.

Hope you enjoyed our post and I’d like to thank Enno, Florian and the great ERNW team for their kind invitation.

You can get more information about our work at

BTW: Meet Mariano Nuñez Di Croce, CEO of Onapsis at TROOPERS12 in about ten days! He will give a talk and also host a dedicated workshop on SAP security.

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Applying the ERNW Seven Sisters Approach to VoIP Networks


if you’re following this blog regularly or if you’ve ever attended an ERNW-led workshop which included an “architecture section” you will certainly remember the “Seven Sisters of Infrastructure Security” stuff (used for example in this post). These are a number of (well, more precisely, it’s seven ;-)) fundamental security principles which can be applied to any complex infrastructure, be that a network, a building, an airport or the like.

As part of our upcoming Black Hat and Troopers talks we will apply those principles to some VoIP networks we (security-) assessed and, given we won’t cover them in detail there, it might be helpful to perform a quick refresher of them, together with an initial application to VoIP deployments. Here we go; these are the “Seven Sisters of Infrastructure Security”:

  • Access Control
  • Isolation
  • Restriction
  • Encryption
  • Entity Protection
  • Secure Management
  • Visibility

Now, let me discuss them in a bit more detail and put them into a VoIP context.


Access Control (“try to keep the threats out of the environment containing the assets to be protected”)

This should pretty much always be an early consideration as limiting access to “some complex infrastructure” obviously provides a first layer of defense and does so in a preventative[1] way. Usually authentication plays a major role here. Please note that in computer networks the access control principle does not only encompass “access to the network [link]” (where unfortunately the most prevalent technology – Ethernet – does not include easy-to-use access control mechanisms. And, yes, I’m aware of 802.1X…) but can be applied to any kind of (“sub-level”) communication environment or exchange. Taking a “passive-interface” approach for routing protocols is a nice example here as this usually serves to prevent untrusted entities (“the access layer”) from participating in some critical protocol [exchange][2] at all.

In a VoIP scenario limiting who can participate in the various layers and communication exchanges, be it by authentication, be it by configuration of static communication peers for certain exchanges[3] (yes, we know this might not scale and usually has a bad operational feasibility) would be an implementation of the access control principle.


Isolation (“separate some elements of the environment from others, based on attributes like protection need, threat potential or trust/worthiness”)

In computer networks this one is usually implemented by network segmentation (with different technologies like VLANs or VRFs and many others) and it’s still one of the most important infra­structure security principles. I mean, can you imagine an airport or corporate headquarters without areas of differing protection needs, different threat exposure or separate layers and means of access? [You can’t? So why do you think about virtualizing all your corporate computer systems on one big unified “corporate cloud”? ;-)]

Again, it should be noted that “traditional network segmentation” is only one variant. Using RFC 1918 (or ULA, for that matter) addresses in some parts of your network without NATing them at some point, or refraining from route distribution at some demarcation point constitute other examples.

In the VoIP world the main realization of the isolation principle is the commonly found approach of “voice vs. data VLAN[s]”.


Restriction (“once [as of the above principle] isolated parts get connected try to limit the interaction between those parts at the intersection point”)

This is the one most people think of when it comes to network security as this is what the most widely deployed network security control, that is firewalls, is supposed to do.

Two points should be noted here, from our perspective:

In some network security architecture documents phrases going like “the different segments are [to be] separated by firewalls” can be found. Which, well, is a misconception: usually a firewall connects networks (which would be isolated otherwise), it does not separate them. It may (try to) limit the traffic passing the intersection point but it still is a connection element.

And it should be noted that the restriction it applies (by filtering traffic) always has an operational price tag. Which is the one of the reasons why firewalls nowadays tend to fail so miserably when it comes to their actual security benefit…

In VoIP networks using the restriction approach is considerably hard (and hence quite often simply doesn’t happen) given a number of protocols’ volatility when it comes to the (UDP/TCP) ports they use.
Encryption (“while in transit encrypt some asset to protect it from threats on its [transit] way”)
This is a very common infrastructure security control as well (alas, at times the only one people think of) and probably does not need further explanation here.

Still it should be noted – again – that it has an operational price tag (key management and the like). Which – again – is the very reason why it sometimes fails so miserably when it comes to providing actual security…

In the VoIP world (as this one is very much about “assets in transit”) it’s (nowadays) a quite common one, even though still a number of environments refrains from using it, mainly due to the mentioned “operational price tag”.
Entity Protection (“take care of the security exposure of the individual elements within the environment containing the assets to be protected”)

This encompasses all measures intended to increase the security of individual elements. It’s not limited to simple hardening though, but includes all other “security [posture] quality assurance” things like pentesting or code reviews (when the element looked at is an application).

Adding a comment again I’d like to state that, in times of virtualization and vaporizing security layers (deploying shiny apps pretty much directly connecting customers to your ERP systems, by means of fancy webservices) this one might become more and more important. In the past many security architectures relied on layers of isolation & restriction and thereby skipped the hardening/quality assurance step (“we don’t have to harden this Solaris box as there’s a firewall in front of it”). As the talks’ case studies will show this one is a fundamental (and overlooked) one in many VoIP deployments.

Secure Management (“manage the [infrastructure] elements in a secure way”)

Secure management usually can be broken down to:

  • Restrict the endpoints allowed to establish management connections.
  • Either use a trusted environment (network link) or use secure variants of mgmt. protocols instead of their less secure counterparts (SSH vs. Telnet, HTTPS vs. HTTP, SNMPv3 vs. community-based SNMP and the like).
  • Require sufficient authentication (as for methods, authenticator [e.g. password] quality, personalized accounts etc.).
  • Logging of security related events and potentially all management actions performed.


While this is (should be) an obvious security principle, daily assessment experience shows that failures/weaknesses in this space account for the majority of critical vulnerabilities when it comes to infrastructure security. This applies in particular to VoIP implementations (see the case studies for examples).

Visibility (“be able to assess the current security posture of your infrastructure and its elements with reasonable effort”)

This is where logging (+ analysis), monitoring etc. come into play. We’d like to note that while this is a valid infrastructure security principle, its actual security benefit is often overestimated given the “detection/reaction” nature of this principle and its subsequent bad operational feasibility.

This is a particularly interesting (and neglected) one in many VoIP environments. Usually the data generated in this space (for VoIP) can not be easily processed (by $SIEM you acquired two years ago, for a six-figure € number and which still has only a handful of use cases defined…), while on the other hand being heavily useful (or even required for legal follow-up) in one of those numerous billing fraud incidents.
How to Apply those Principles in a Generic Way

As the above application to VoIP shows, these fundamental security principles allow for tackling any type of “securing assets within a complex overall setting” by going through a simple (checklist-type) set of questions derived from them. These questions could look like

  • Can we limit who’s taking part in some network, protocol, technology, communication act?
  • Any need to isolate stuff due to different protection need, (threat) exposure or trust(worthiness)?
  • What can be done, filtering-wise, on intersection points?
  • Where to apply encryption in an operationally reasonable way?
  • What about the security of the overall system’s main elements?
  • How to manage the infrastructure elements in a secure way?
  • How to provide visibility as for security-related stuff, with reasonable effort?
In a sequel to this post I might cover the mentioned case studies in more detail. In case I miss doing so, the slides will be available after the respective events ;-).
Have a great Sunday,

[1] As it requires the usually most scarce resource of an organization, that is humans and their brains. The part that can not be easily substituted by technology…

[1] In general preventative controls have a better cost/benefit ratio than detective or reactive ones. And this is still true in the “you’ll get owned anyway that’s why you should spend lots of resources on detective/reactive controls” marketing hype age…

[2] To provide another example from the routing protocol space: the “inter-operator trust and TCP-” based nature of BGP (as opposed to the “multicast and UDP-“based nature of other routing protocols) certainly is one of the most fundamental stability contributing properties of the current Internet.

[3] Another simple example here. If the two VoIP gateways in the incident described here had used a host route for each other instead of their default route (which wasn’t needed given their only function was to talk to each other), presumably the whole thing wouldn’t have happened.


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