Category: BGP

Ignas Bagdonas sent a phenomenal summary of recent BGP developments to the RIPE Routing WG mailing list. Enjoy!

An anonymous commenter asked this highly relevant question about my Internet routing security lab:

What are the smallest hardware requirements to run the lab?

TL&DR: 2 GB RAM, 2 vCPU

Now for the more precise answer (aka “it depends”).

I created a netlab topology you can use to practice BGP security tools I described in the Internet Routing Security webinar:

• The lab topology mirrors the sample topology I described in the Classification of BGP Route Leaks (RFC 7908) blog post with one router per autonomous system
• BGP is configured on all devices, and EBGP sessions are set up between all directly-connected devices.

Andrei Robachevsky asked me to spread the word about the new MANRS+ customer survey:

MANRS is conducting a survey for organizations that contract connectivity providers to learn more about if and how routing security fits into their broader supply chain security strategy. If this is your organization, or if it is your customers, we welcome you to take or share the survey at https://www.surveymonkey.com/r/BDCWKNS

I hope you immediately clicked on the link and completed the survey. If you’re still here wondering what’s going on, here’s some more information from Andrei:

While preparing the Internet Routing Security webinar, I stumbled upon RFC 7908, containing an excellent taxonomy of BGP route leaks. I never checked whether it covers every possible scenario¹, but I found it a handy resource when organizing my thoughts.

Let’s walk through the various leak types the authors identified using the following sample topology:

One of the most common causes of Internet routing leaks is an undereducated end-customer configuring EBGP sessions with two (or more) upstream ISPs.

Without basic-level BGP knowledge or further guidance from the service providers, the customer network engineer¹ might start a BGP routing process and configure two EBGP sessions, similar to the following industry-standard CLI² configuration:

Nicola Modena had an interesting presentation describing how you can use BGP FlowSpec for traffic steering and service insertion during the recent ITNOG 7 event (more about the event in a few days).

One of the slides explained how to use three different aspects of BGP (FlowSpec, MPLS/VPN and multipathing), prompting me to claim the presentation title should be “BGP is the answer, what was the question?” 😉 Hope you’ll enjoy the PDF version of the presentation as much as we did the live one.

When I reposted a link to xBGP: Faster Innovation in Routing Protocols paper, someone immediately replied

Quite interesting, but it feels like this could become the proverbial 15th standard.

xBGP is an API that allows BGP users to implement routing policies (route selection, filtering, or propagation) that use attributes or mechanisms defined in newer IETF RFCs or drafts, so the proverbial 15th standard is not that far off the mark. However, we must remember that what we call BGP is more than just a set of competing standards.

One of my subscribers found an unusual BGP specimen in the wild:

• It was a small site with two core switches and a WAN edge router
• The site had VPN concentrators running in virtual machines
• The WAN edge router was running BGP across WAN IPsec tunnels
• The VPN concentrators were running BGP with core switches.

So far so good, and kudos to whoever realized BGP is the only sane protocol to run between virtual machines and network core. However, the routing in the network core was implemented with EBGP sessions between the three core devices, and my subscriber thought the correct way to do it would be to use IBGP and OSPF.

BGP zombies are routes in the BGP table that refuse to disappear even though they should have been long gone. Recent measurements estimate between 0.5% and 1.5% of all routes in the global BGP table are zombies, which sounds crazy – after all, BGP is supposed to be pretty reliable.

Daryll Swer identified one potential source – Juniper routers do not revoke suppressed aggregated prefixes – and documented it in Navigating a BGP zombie outbreak on Juniper routers.

I got this question from one of my readers:

Why are OSPF and BGP are more complex than STP from a designer or administrator point of view? I tried everything to come to a conclusion but I couldn’t find a concluded answer, ChatGPT gave a circular loop answer.

There are numerous reasons why a protocol, a technology or a solution might be more complex than another seemingly similar one (or as Russ White would have said, “if you haven’t found the tradeoffs, you haven’t looked hard enough”):

One of my subscribers sent me this question:

I’m being asked to enter a working group on RPKI and route origination. I’m doing research, listening to Jeff Tantsura, who seems optimistic about taking steps to improve BGP security vs Geoff Huston, who isn’t as optimistic. Should I recommend to the group that the application security is the better investment?

You need both. RPKI is slowly becoming the baseline of global routing hygiene (like washing hands, only virtual, and done once every blue moon when you get new IP address space or when the certificates expire). More and more Internet Service Providers (including many tier-1 providers) filter RPKI invalids thus preventing the worst cases of unintentional route leaks.

I wanted to include a few examples of BGP bugs causing widespread disruption in the Network Security Fallacies presentation. I tried to find what happened when someone announced beacon prefixes with unknown optional transitive attributes (which should have been passed without complaints but weren’t) without knowing when it happened or who did it.

Trying to find the answer on Google proved to be a Mission Impossible – regardless of how I structured my query, I got tons of results that seemed relevant to a subset of the search words but nowhere near what I was looking for. Maybe I would get luckier with a tool that’s supposed to have ingested all the world’s knowledge and seems to (according to overexcited claims) understand what it’s talking about.

A few weeks ago I described why EBGP TCP packets have TTL set to one (unless you configured EBGP multihop). Although some people claim that (like NAT) it could be a security feature, it’s not a good one. Generalized TTL Security Mechanism (GTSM, described in RFC 5082) is much better.

Most BGP implementations set TTL field in outgoing EBGP packets to one. That prevents a remote intruder that manages to hijack a host route to an adjacent EBGP peer from forming a BGP session as the TCP replies get lost the moment they hit the first router in the path.

Chris Parker wrote a wonderful blog post going deep into the weeds on how EBGP sessions use IP TTL and why we need multihop EBGP sessions between adjacent devices. However, he couldn’t find a source explaining why early BGP implementations decided to use IP TTL set to one on EBGP sessions:

If there’s a source on the internet that explains when it was decided that EBGP should use a TTL of 1, I can’t find it. I can’t even find it in any RFC. I looked in the RFC for BGP v4, and went all the way back to BGP v1. None of these documents contain the text “TTL or “time to live” or “time-to-live.” It’s not even in the RFC for EGP, back in 1984.