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BGP and IPv6 routing courses

Several times a year I teach two training courses, one about BGP and one about IPv6. The BGP course is half theory and half hands-on practice, and so is the new IPv6 routing course. Previously, we did an IPv6 course without a hands-on part.

The courses consists of a theory part in the morning and a practical part in the afternoon where the participants implement several assignments on a Cisco router (in groups of two participants per router).

Dates for upcoming courses in 2015 are:

  • June 1: BGP (English)
  • June 2: IPv6 routing (English)
  • October 5: BGP (probably in Dutch)
  • October 6: IPv6 routing (probably in Dutch)
Go to the NL-ix website to find more information and sign up. The location will be The Hague, Netherlands.

Interdomain Routing & IPv6 News

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  • Documentation ASNs and IP prefixes (posted 2015-04-24) article 163

    As you may have noticed, I write about BGP from time to time. When coming up with example configurations, there's always the challenge of which AS numbers and IP addresses/prefixes to use. Although it's unlikely people will simply copy numbers and addresses from examples into their own BGP configurations, experience with NTP has shown that this can be a real problem, so it's a good idea to avoid "real" addresses and numbers in examples.

    One obvious choice for IPv4 addresses in examples is the RFC 1918 space:, and For IPv6, you could use the unique (site) local addresses (ULA, RFC 4193: fc00::/7, or, more precisely, the ones you get to generate yourself in fd00::/8. I wouldn't recommend using the original site local IPv6 addresses (fec0::/10), as these are "deprecated" in RFC 3879.

    For AS numbers, there's the private range 64512 - 65534 (16 bit) and 4200000000 - 4294967294 (32 bit) in the IANA registry.

    However, there are also address and AS number ranges specifically set aside for example and documentation use. These have the advantage that they can easily be recognized as being intended for documentation, and won't clash with ranges used in private networks. They are:

    • 16-bit AS numbers: 64496 - 64511 (RFC 5398)
    • 32-bit AS numbers: 65536 - 65551 (RFC 5398)
    • IPv4 addresses:,, (RFC 5737)
    • IPv6 addresses:2001:db8::/32 (as in "debate") (RFC 3849)

    I actually didn't know about the documentation AS number ranges and the second and third IPv4 documentation ranges. The extra IPv4 ranges will be very useful, as just often isn't enough in more complex BGP examples, especially as I don't want to give the impression that it's possible to deaggregate a /24 into smaller parts. The 16-bit documentation AS numbers will also be useful. Unfortunately, the 32-bit ones aren't really useful as they look too much like 16-bit numbers. However, the 65552 - 131071 range is "reserved" so I guess I'll continue to use AS numbers in the 9xxxx range as examples of 32-bit ASNs.

  • "Get Your Hands Dirty with BGP" tutorial at next month's RIPE meeting (posted 2015-04-15) article 162

    At the RIPE-70 meeting next month in Amsterdam I'll be doing a tutorial on BGP: "Get Your Hands Dirty with BGP".

    This is the "light" version of the regular BGP training that I do several times a year: the theory part will be around 30 minutes and then about two hours of hands-on BGP using the Quagga routing software running in a virtual machine on the participant's laptops.

    If you're attending the RIPE meeting and you're interested in participating, please go to this page and send me an email so I know how many people to expect.

  • "no synchronization" in Cisco configurations (posted 2015-02-04) article 161

    This text used to be on the home page, but Cisco now includes "no syncronization" in the default configuration, so it's unlikely anyone is still going to run into trouble because of this, so I've moved this to a separate page out of the way.

    When you run BGP on two or more routers, you need to configure internal BGP (iBGP) between all of them. If those routers are Cisco routers, they won't work very well unless you configure them with no synchronization.

    Read the whole article

  • Comparing open source routing platforms (posted 2015-02-02) article 160

    Over the weekend, I wrote posts about trying out OpenBGPD and BIRD.

    Here's a bunch more information about these two and other open source routing software:

    Basically, OpenBGPD's filtering system has scalability issues, and it uses a lot of CPU in large deployments. And it concerns me that these mention OpenBGPD 4.8 and 5.0, while the website only has 4.6.

    And I guess I have some homework: install Xorp, a Juniper-like open source routing platform. Archives of all articles - RSS feed

My Books: "BGP" and "Running IPv6"

On this page you can find more information about my book "BGP". Or you can jump immediately to chapter 6, "Traffic Engineering", (approx. 150kB) that O'Reilly has put online as a sample chapter. Information about the Japanese translation can be found here.

More information about my second book, "Running IPv6", is available here.

BGP Security

BGP has some security holes. This sounds very bad, and of course it isn't good, but don't be overly alarmed. There are basically two problems: sessions can be hijacked, and it is possible to inject incorrect information into the BGP tables for someone who can either hijack a session or someone who has a legitimate BGP session.

Session hijacking is hard to do for someone who can't see the TCP sequence number for the TCP session the BGP protocol runs over, and if there are good anti-spoofing filters it is even impossible. And of course using the TCP MD5 password option (RFC 2385) makes all of this nearly impossible even for someone who can sniff the BGP traffic.

Nearly all ISPs filter BGP information from customers, so in most cases it isn't possible to successfully inject false information. However, filtering on peering sessions between ISPs isn't as widespread, although some networks do this. A rogue ISP could do some real damage here.

There are now two efforts underway to better secure BGP:

  • Secure BGP (S-BGP) is developed by Bolt, Beranek and Newman (BBN). It has been around for several years and there is a proof-of-concept implementation. S-BGP tries to secure all aspects of the BGP protocol, and subsequently needs several signature checks for each BGP update, making the protocol relatively heavy-weight. You can see my earlier rants on S-BGP at the top of this page. Note that I'm not as anti-S-BGP as I used to be any more, although I still think implementing the protocol will be expensive because routers will need lots of extra memory (up to four times as much) and CPU power (possibly dedicated crypto hardware) and this aspect deserves some serious attention.

    Secure BGP (S-BGP) index at BBN.

  • Secure Origin BGP (soBGP) has surfaced fairly recently and hails from Cisco. There are no implementations so far. soBGP mainly focusses on securing the relationship between prefixes and the source AS number, and doesn't need as many computationally expensive checks as S-BGP. However, the protocol can easily be expanded to perform more checks.

    draft-ng-sobgp-bgp-extensions-00.txt (main soBGP draft)
    draft-white-sobgp-bgp-extensions-00.txt (deployment considerations)

    (If the links don't work, the drafts have expired; you'll have to use a search engine to find them.)

There is now also a different approach to increasing BGP security using an "Interdomain Routing Validation" service that works independent from the BGP protocol itself. See what I wrote about this in interdomain routing news on this site, or jump immediately to the Working Around BGP: An Incremental Approach to Improving Security and Accuracy of Interdomain Routing paper.

The IETF RPSEC (routing protocol security) working group is active in this area.

What is is a website dedicated to Internet routing issues. What we want is for packets to find their way from one end of the globe to another, and make the jobs of the people that make this happen a little easier.

Your host is Iljitsch van Beijnum. Feedback, comments, link requests... everything is welcome. You can read more about me here or email me at iljitsch@bgpexpert. or follow iljitsch on Twitter.

Ok, but what is BGP?

Have a look at the "what is BGP" page. There is also a list of BGP and interdomain routing terms on this page.

BGP and Multihoming

If you are not an ISP, your main reason to be interested in BGP will probably be to multihome. By connecting to two or more ISPs at the same time, you are "multihomed" and you no longer have to depend on a single ISP for your network connectivity.

This sounds simple enough, but as always, there is a catch. For regular customers, it's the Internet Service Provider who makes sure the rest of the Internet knows where packets have to be sent to reach their customer. If you are multihomed, you can't let your ISP do this, because then you would have to depend on a single ISP again. This is where the BGP protocol comes in: this is the protocol used to carry this information from ISP to ISP. By announcing reachability information for your network to two ISPs, you can make sure everybody still knows how to reach you if one of those ISPs has an outage.

Want to know more? Read A Look at Multihoming and BGP, an article about multihoming I wrote for the O'Reilly Network.

For those of you interested in multihoming in IPv6 (which is pretty much impossible at the moment), have a look at the "IPv6 multihoming solutions" page.

Are you a BGP expert? Take the test to find out!

These questions are somewhat Cisco-centric. We now also have another set of questions and answers for self-study purposes.

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