ShortestPathFirst Network Architecture and Design, and Information Security Best Practices

30Nov/091

Book Review :: MPLS-Enabled Applications: Emerging Developments and New Technologies

MPLS Enabled Applications

MPLS-Enabled Applications: Emerging Developments and New Technologies
by Ina Minei, Julian Lucek
Paperback: 526 pages
Publisher: Wiley
ISBN-13: 978-0470986448

5starsExcellent coverage of VPLS, and Multicast over Layer 3 VPNs

Recently I had to work on a project which involved demonstrating Multicast over Layer 3 VPN interoperability between Cisco and Juniper. I spent several days reading through all the RFCs and working-group drafts which pertained to this subject matter, after which I still had many unanswered questions. In order to round out my understanding, I decided to order the Second Edition of 'MPLS-Enabled Applications'. Looking back, I wish I had read this book instead of wasting my time reading the various RFCs and working-group drafts. This book answered all of my questions and went above and beyond to give me a solid understanding of the concepts and their application. As other reviewers have pointed out, often one needs to read a book to understand the technology basics, and then refer to RFCs or working-group drafts in order to keep abreast of the latest changes. Not so with this book... In fact, this book is so current that reading the working-group drafts is largely unnecessary. It is incredibly comprehensive, concise, and gives the reader a thorough understanding of the business drivers. Furthermore, it illustrates the various ways in which MPLS services can be offered and outlines the pros and cons of each approach so that the network designer can make intelligent decisions with regards to implementation.

In addition to the great coverage that was provided by the First Edition, the Second Edition has updated the text to reflect newer trends and applications such as the transport of IPv6 over an IPv4 MPLS core, and detailed coverage of end-to-end and local protection schemes in MPLS networks. Likewise, the chapter previously called "Point-to-Multipoint LSPs" has now been renamed to "MPLS Multicast", with much more detailed coverage of the P2MP hierarchy and the forwarding-plane and control-plane operation. The biggest value for me was the addition of a completely new chapter on "Multicast over Layer 3 VPNs" which provided comprehensive coverage of this emerging technology and fully illustrates the full gamut of operation of either the PIM/GRE approach, or the NG-VPN approach utilizing BGP and P2MP LSPs. Finally, the addition of a chapter on "MPLS in Access Networks" was well deserved seeing as Ethernet is quickly becoming the access technology of choice and MPLS will likely be utilized as an overlay in order to realize the full potential of Ethernet in these environments.

This book has earned a spot on my bookshelf as one of my most coveted resources, and I refer to it quite often to refresh my memory on the myriad workings of various functions within MPLS. I wish I could give this book a rating higher than five stars! I can't overemphasize how exceptional this book is. If you are in the market for a book covering MPLS and emerging applications offered on MPLS networks, this single book should be at the top of your list!

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20Nov/094

The Case for Juniper Press

When was the last time you went into a bookstore and found a book on the bookshelf covering Juniper technologies?  I've managed to rarely, if ever, find more than one or two titles on JUNOS or any sort of Juniper related technology.  On the other hand, you'd be hard pressed to miss the bevy of Cisco related titles covering a vast array of technologies and platforms.  When I teach Juniper classes, or I'm on a consulting gig pitching Juniper technologies, one of the things I hear most often is that there aren't enough resources available to people who want to learn more about JUNOS.  Often the answer is "Well, there's the Fast Track Program", or "Well, you can download the free books by Joe Soricelli or Harry Reynolds" (which by the way, it's high time we get those books back in print - they are excellent books, well written, and in my opinion, second to none when preparing for the Service Provider track).  But often this isn't enough for the folks who want to learn more.  While Juniper's Fast Track Program is an extremely valuable resource, it's coverage is limited to only a few select technologies.  Furthermore, beyond a handful of books on Amazon, there aren't many additional resources outside of reading Juniper's technical documentation or various white papers for those students who truly wish to expand their knowledge base.  Sure, the JNCIA-M/T, JNCIS-M/T, JNCIP-M/T, and JNCIE-M/T study guides are freely available, but more often than not people would prefer to have these in hardcopy format rather than in a PDF and printing a PDF doesn't provide the reader with quite the same experience.  I don't care what anyone thinks, electronic formats aren't going to be replacing printed books anytime soon.  Just ask yourself when was the last time you read an entire book on a computer screen?  NOTE TO AUTHORS: A Kindle version would be nice and this would be a good first step, but then again, how many people do you know that actually own a Kindle?

In 1996, when Cisco Press was formed as a joint publishing partnership with Pearson Education, Cisco realized that providing educational materials to meet the growing demand for networking technologies was going to be a cornerstone to their success.  In 1997, "Internet Routing Architectures" by Sam Halabi rolled off the printing press and was an instant best seller.  The rest was pretty much history.  Cisco understood early on that there was a vacuum in the market for high-quality technical books covering the networking arena, and more specifically Cisco technologies.  They met that demand and incidently watched their market share grow to the behemoth they are today.  Since its inception, Cisco Press has published well over 400 titles.  It's no surprise that given a wealth of educational resources at their disposal, engineers who understand a given technology are more apt to recommend those technologies to their peers, and more importantly, to the people who often end up buying the technology. One only needs to look at the 20,000+ CCIEs in the world today to understand thats a pretty big propaganda machine to silence.

I've worked with both Cisco and Juniper technologies for a long time, and I'm convinced that Juniper's products are infinitely superior, but if Juniper is serious about being a major competitor, especially in the Enterprise market or other market segments outside of the Service Provider arena, it's high time they think about creating a publication arm which can compete with the likes of Cisco Press.  It might not be the most profitable business, and in fact, if you're simply looking at dollars and cents with a microscopic view, it might even be a losing proposition.  But the demand is out there, and if they meet it, I am fairly certain Juniper will see their marketshare increase in a really big way.

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Filed under: Juniper 4 Comments
15Nov/093

An Overview of BGP FlowSpec

I have given this presentation a few times in the last year and was asked to make this available for public consumption. Essentially, this is a brief overview of RFC 5575, entitled “Dissemination of Flow Specification Rules”, written by Danny McPherson, Jared Mauch, and others. This standard had somewhat of a rocky beginning as there was limited vendor support, but as of recently it appears to have picked up quite a bit of steam with Cisco announcing support for the protocol in the very near future. The benefit of BGP Flow Spec is that it allows BGP speakers to use a new BGP NLRI defining flow filter information which can then be advertised to upsteam neighbors via BGP. The primary and immediate motivation of this protocol is to provide intra and inter provider distribution of traffic filtering rules to filter DoS and DDoS attacks, however it can be used for a wide variety of applications in which filtering information must be dynamically distributed throughout a network. I will probably make additional modifications to these slides as the protocol gains more significant foothold throughout the vendor community and as Service Providers gain more practical deployment experience. As with my other presentations, I will eventually add a voice-over to turn this into a slide-cast.

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13Nov/090

IP Routing Tutorial

I've given this tutorial quite a few times now and several people have asked me to make it publicly available. This is very much geared towards non-technical folks who would like to have a better understanding of how routing in the Internet works. It covers a brief history of the Internet and evolution of dynamic routing protocols, as well as high-level coverage of link-state vs. distance vector IGPs in addition to discussing EGPs and their role in the exchange of routing information between Autonomous Systems. It also has a few slides on QoS, MPLS, and IPv6. I would still like to make some modifications to a few of the slides as well as adding more content around MPLS and the future of IP.  I will also eventually add a voice-over to turn this into a true slide-cast.  In the meantime, I've put it up on my slideshare account for those of you who would like to have access to it.

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12Nov/091

Hardening DNS Against Reflection Attacks

Generally, the most prevalent types of attacks and the ones which are most likely to target a DNS infrastructure are reflection/amplification attacks (which generally use a DNS servers resources against other third-parties).  Understanding the attack-vector employed in most reflection attacks is necessary in order to understand how to harden an environment against these types of attacks.

In a typical DNS reflection attack, attackers send a large number of queries from a spoofed source address.  The address which is spoofed is typically that of the victim.  When the requests are received by the nameserver, all ensuing responses to these queries are directed back towards the spoofed IP of the victim.  The amplification factor comes into play in these types of attacks because the attacker will typically query for a record of a large size, typically that of a root record which by it's very nature is very large in size.  By simply sending in small queries, on the order of around 90 Bytes, an attacker can typically get a multiplication factor of five times that of the original query.  This allows an attacker to use a smaller number of hosts in the botnet and cause considerably more impact than would otherwise be possible if these devices were sending traffic directly towards the victim.

Due to the fact that the purpose of this attack is to reflect packets back towards the victim, all of the source IPs of the DNS queries contain the same address.  This makes it fairly easy to spot a reflection attack utilizing your infrastructure.  A simple observation of a spike in DNS queries from a singular IP is a clear indication that this is going on.  One would think that these types of attacks can be mitigated fairly easily by implementing simple ACLs on routers to prevent the incoming queries from those spoofed IP, and in fact that is a method commonly used by network administrators to protect against these types of attacks.  However, most security experts suggest that the filtering should actually be implemented on the nameserver itself - in fact this has been considered an industry best practice for quite some time now.  The reason for this is that implementing an ACLs on a router is largely a reactive countermeasure which can only be deployed after the fact.  An administrator will still need to identify the target of the attack before filters can be put in place; furthermore these types of filters only serve to cause a legitimate Denial of Service when that particular victim actually attempts to query anything for which the nameserver is actually authoritative for.  As an alternative to ACLs, some proposed configurations below can be used to eliminate this problem in it's entirety.

At the very onset of your investigation into the vulnerabilities of your DNS infrastructure and potential remedies one of the very first things a network administrator must determine is if the nameservers allow anyone on the outside world to query for root (.).  Using the example below, one can easily check to see if their nameserver responds with a root-referral when queried for root.  If you see something along these lines, you can be fairly certain your nameserver is responding with a root-referral:

/usr/bin/dig . NS @dns.example.com
 
; <<>> DiG 9.2.4 <<>> . NS @DNS.EXAMPLE.COM ; (2 servers found) ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54368 ;; flags: qr rd; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 13
 
;; QUESTION SECTION:
;. IN NS
 
;; ANSWER SECTION:
. 86400 IN NS A.ROOT-SERVERS.NET.
. 86400 IN NS B.ROOT-SERVERS.NET.
. 86400 IN NS C.ROOT-SERVERS.NET.
. 86400 IN NS D.ROOT-SERVERS.NET.
. 86400 IN NS E.ROOT-SERVERS.NET.
. 86400 IN NS F.ROOT-SERVERS.NET.
. 86400 IN NS G.ROOT-SERVERS.NET.
. 86400 IN NS H.ROOT-SERVERS.NET.
. 86400 IN NS I.ROOT-SERVERS.NET.
. 86400 IN NS J.ROOT-SERVERS.NET.
. 86400 IN NS K.ROOT-SERVERS.NET.
. 86400 IN NS L.ROOT-SERVERS.NET.
. 86400 IN NS M.ROOT-SERVERS.NET.
 
;; ADDITIONAL SECTION:
A.ROOT-SERVERS.NET. 86400 IN A 198.41.0.4
B.ROOT-SERVERS.NET. 86400 IN A 192.228.79.201
C.ROOT-SERVERS.NET. 86400 IN A 192.33.4.12
D.ROOT-SERVERS.NET. 86400 IN A 128.8.10.90
E.ROOT-SERVERS.NET. 86400 IN A 192.203.230.10
F.ROOT-SERVERS.NET. 86400 IN A 192.5.5.241
G.ROOT-SERVERS.NET. 86400 IN A 192.112.36.4
H.ROOT-SERVERS.NET. 86400 IN A 128.63.2.53
I.ROOT-SERVERS.NET. 86400 IN A 192.36.148.17
J.ROOT-SERVERS.NET. 86400 IN A 192.58.128.30
K.ROOT-SERVERS.NET. 86400 IN A 193.0.14.129
L.ROOT-SERVERS.NET. 86400 IN A 199.7.83.42
M.ROOT-SERVERS.NET. 86400 IN A 202.12.27.33
 
;; Query time: 43 msec
;; SERVER: www.example.com#53(www.example.com)
;; WHEN: Thu Nov 12 17:01:51 2009
;; MSG SIZE rcvd: 436
 

Normally, most Internet-facing authoritative nameservers should not respond to recursive third-party queries for root.  If an authoritative nameserver responds to queries for root with a root-referral, attackers will likely use your nameservers as an amplification vector to launch attacks.  It is better to remove the temptation altogether, by not allowing these in the first place.  Furthermore, instead of responding with the root-referral, nameservers should be configured to respond with REFUSED or SERVFAIL or another similar type of message.  The reason for this is simple - a REFUSED message is only on the order of around 50 Bytes.  If a countermeasure such as this is not employed, attackers can send in a relatively small spoofed query and will get roughly a 512 Byte response.  However, if we respond with a REFUSED message, the amplification factor is on the order of 1:1.  From an efficiency standpoint this does not provide much if any amplification, and therefore the attackers will simply look for other providers whom don’t apply such stringent security measures.

NOTE: Of course if you are in the business of providing recursive DNS service, that is an entirely different story - if that is the case, network administrators should take extra precautions by strictly enabling this function on the Recursive DNS servers (not the Authoritatives) and combining firewall-filters to limit recursive service to only IP blocks of paying customers.
 
While we're on the subject, another current best practice in the industry is to apply a similar methodology to requests for records for which a given DNS Server is not authoritative for.  Some resolvers may respond to these types of requests by providing a root-referral, and in the worst cases a resolver may actually perform a recursive query on behalf of the original source.  An authoritative resolver should respond to any non-existent domain requests with either the REFUSED message or other similar type of message, rather than providing a root referral or performing a recursive query.  In fact, BCP 140 (Preventing Use of Recursive Nameservers in Reflector Attacks, RFC 5358) looked at this problem and concluded that sending REFUSED was the best general guidance that can be given.  While BCP 140 applies guidance to recursive servers, returning REFUSED to queries which are not within the namespace served by authoritative servers is entirely consistent with BCP 140.  You can generally find out if your nameservers allows for recursion or if it responds with a root-referral, by using a command such as the following:

/usr/bin/dig +recurs @yournameserver_ip www.facebook.com
 

If you see a response which looks like the large root-referral response above, or some other type of response other than a REFUSED or SERVFAIL, you should take steps to harden your resolver.  One can also look for an "RA" entry in the "Flags" section of the DNS response which should give you some indication as to whether the resolver allows for recursion.

In conclusion, there are several such steps which allow administrators to prevent from being used as an unwitting pawn in an attack against third-parties.  Firewall filters are effective, but are reactive in nature.  Therefore, it is recommended to follow some of the steps below in order to effectively harden your DNS infrastructure against reflection attacks.

SYNOPSIS - Steps to prevent a DNS infrastructure from being used for reflection/amplification type attacks:

  1. Disable querying for root on Authoritative resolvers, return REFUSED
  2. Filter queries to Recursives from only paying customers, via ACLs
  3. Apply BCP 140 or similar rules to cause any non-existent domain queries to respond with a REFUSED.

An excellent whitepaper entitled "Anatomy of Recent DNS Reflector Attacks from the Victim and Reflector Point of View" by Ken Silva, Frank Scalzo and Piet Barber covers this topic in more detail.

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12Nov/090

Reflections on the Past :: ConneXions – The Interoperability Report

Way back in 1987, before there was the the "Internet Protocol Journal" and other notable publications which cover various aspects of Internet Technologies, there was "ConneXions - The Interoperability Report".   At the time, aside from reading RFCs or Internet-Drafts for more information on various protocols, this publication was the defacto resource for informative analysis of various protocols and their operation.  A quick glance at the articles and you'll see long-time industry heavy-hitters such as Doug Comer, Jon Postel, and Vint Cerf listed as the authors.  This is an invaluable resource for those of you who want to understand the history and evolution of various Internet protocols commonly in use today.

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