BGP handling bug causes widespread internet routing instability
164 comments
·May 27, 2025ta1243
zajio1am
There is already RFC 7606 (Revised Error Handling for BGP UPDATE Messages), which specifies in detail how broken BGP messages should be handled.
The most common approach is 'treat-as-withdraw', i.e. handle the update (announcement of a route) as if it was a withdraw (removal of previously announced route). You should not just drop the broken message as that whould lead to keeping old, no longer valid state.
timewizard
[flagged]
hannob
> The standard approach is be liberal in what you accept and be specific in what you emit.
What you're paraphrasing here is the so-called "robustness principle", also known as "Poestel's law". It is an idea from the ancient history of the 1980s and 09s Internet. Today, it's widely understood that it is a misguided idea that has led to protocol ossification and countless security issues.
senderista
Postel's Law certainly has led to a lot of problems, but is it really responsible for protocol ossification? Isn't the problem the opposite, e.g. that middleboxes are too strict in what they accept (say only the HTTP application protocol or only the TCP and UDP transport protocols)?
fc417fc802
Overly strict and overly liberal both lead to ossification. That's merely the observation that buggy behavior in either direction can potentially come to be relied on (or to be unpredictably forced on you, in the case of middleboxes filtering your traffic).
I'd only expect security issues to result from being overly liberal but 1. I wouldn't expect it to be very common and 2. I'm not at all convinced that's a compelling argument to reduce the robustness of an implementation.
AnthonyMouse
The trouble is it fails to specify what you're supposed to be liberal with.
Suppose you get a message that violates the standard. It has a length field for a subsection that would extend beyond the length of the entire message. Should you accept this message? No, burn it with fire. It explicitly violates the standard and is presumably malicious or a result of data corruption.
Now suppose you get a you don't fully understand. It's a DNS request for a SRV record but your DNS cache was written before SRV records existed. Should you accept this message? Yes. The protocol specifies how to handle arbitrary record types. The length field is standard regardless of the record type and you treat the record contents as opaque binary data. You can forward it upstream and even cache the result that comes back without any knowledge of the record format. If you reject this request because the record type is unknown, you're the baddies.
thaumasiotes
It's a description of how natural language is used, so what you'd expect is constant innovation, with protocols naturally developing extensions that can only be understood within local communities, even though they aren't supposed to.
Something like "this page is best viewed in Internet Explorer" as applied to HTML.
fc417fc802
> Today, it's widely understood that ...
Widely claimed by some but certainly not "widely understood" because such phrasing implies a lack of controversy regarding the claim that follows it.
oblio
It's kind of common sense, though. Look at HTML. So badly/under defined that it wasn't even testable for close to 2 decades.
The sane approach is to be strict and provide great error messages.
arccy
[flagged]
lambdaone
Postel's law is absolutely great if you want to make new things and get them going in a hurry, and I think it was one of the major reasons the TCP/IP stack beat the ISO model. But as you say, it's a disaster if you want to build large robust systems for the long term.
arp242
1970s was also just a different time: documentation was harder to get, it was harder to do quality implementations for protocols, people had less of an idea what may or may not work because everyone was new at this (both in terms of protocols and implementations), shipping bugfixes took a lot longer, few people were writing tests (and there wasn't a standard test suite), few people had long experience with these protocols, and general quality of software was a lot lower.
sc68cal
The problem is that folks took advantage of the behavior of BGP where it would forward unknown attributes that the local device didn't understand, as a means to do all sorts of things throughout the network. People now rely on that behavior.
Now, we're experiencing the downside of this "feature"
spwa4
BGP has classes attributes that it forwards. While it is true that it forwards route attributes it doesn't know about, this was an attribute that it DID know about and knows it shouldn't forward.
In fact it's a bit strange just how lenient Juniper's software was here. If a session is configured as IBGP on one end and EBGP on the other end, it should never get past the initial message. Juniper not only let it get past the connection establishment but forwarded obviously wrong routes.
sc68cal
Yes but you are seeing a symptom of what I believe is a fundamental design decision to be liberal in passing on data and then _later_ go through and build logic that stops certain things from being forwarded, and the result is that things slip through the cracks that shouldn't.
Rather than the inverse where you only forward things explicitly and by default do not forward.
icehawk
As far as I'm aware "a session is configured as IBGP on one end and EBGP on the other end" isn't possible.
You can't configure it like that, most of the BGP implementations I'm familiar with automatically treat the a same-AS neighbor as iBGP and a different-AS neighbor as eBGP.
Juniper explicitly has 'internal' and 'external' neighbors, but you can't configure a different peer AS than your own on an internal neighbor or the same peer AS on an external neighbor.
BGP sessions also have the AS of the neighbor specified in the local config, and will not bring up the session if it's not what's configured.
billfor
Author makes this point in a related post:
At a glance this “feature” seems like an incredibly bad idea, as it allows possibly unknown information to propagate blindly through systems that do not understand the impact of what they are forwarding. However this feature has also allowed widespread deployment of things like Large Communities to happen faster, and has arguably made deployment of new BGP features possible at all.
klysm
I disagree with this approach. Being very very specific in what you accept and very very specific in what you emit seems better to me.
erincandescent
Being that prescriptive is fundamentally unworkable in practice. Propagating unknown attributes is fundamentally what made the deployment of 32-bit AS numbers possible (originally RFC 4893; unaware routers pass the `AS4_PATH` attribute without needing to comprehend it), large communities (RFC 8092), the Only To Customer attribute (RFC 9234) and others.
A BGP Update message is mostly just a container of Type-Length-Value attributes. As long as the TLV structure is intact, you should be able to just pass on those TLVs without problems to any peers that the route is destined for.
The problem fundamentally is three things:
1. The original BGP RFC suggests tearing down the connection upon receiving an erroneous message. This is a terrible idea, especially for transitive attributes: you'll just reconnect and your peer will resend you the same message, flapping over and over, and the attribute is likely to not even be your peer's fault. The modern recommendation is Treat As Withdraw, i.e. remove any matching routes from the same peer from your routing table.
2. A lack of fuzz testing and similar by BGP implementers (Arista in this case)
3. Even for vendors which have done such testing, a number of have decided (IMO stupidly) to require you to turn on these robustness features explicitly.
hinkley
PNG solved this problem when BGP was still young: each section of an image document is marked as to whether understanding it is necessary to process the payload or not. So image transform and palette data is intrinsic, but metadata is not. Adding EXIF for instance is thus made trivial. No browser needs to understand it so it can be added without breaking the distribution mechanism.
Diggsey
You're suggesting that being liberal in what you accept is necessary for forward evolution of the protocol, but I think you're presenting a false dichotomy.
In practice there are many ways to allow a protocol to evolve, and being liberal in what you accept is just about the worst way to achieve that. The most obvious alternative is to version the protocol, and have each node support multiple versions.
Old nodes will simply not receive messages for a version of the protocol they do not speak. The subset of nodes supporting a new version can translate messages into older versions of the protocol where it makes sense, and they can do this because they speak the new protocol, so can make an intelligent decision. This allows the network to function as a single entity even when only a subset is able to communicate on the newer protocol.
With strict versioning and compliance to specification, reference validators can be built and fitted as barriers between subnetworks so that problems in one are less likely to spread to others. It becomes trivial for anyone to quickly detect problems in the network.
tinco
That's in conflict with the philosophy behind the internet. If you'd just drop anything because some part of it you don't understand, you lose a lot of flexibility. You have to keep in mind that some parts of the internet are running on 20 year old hardware, but some other parts might work so much better if some protocol is modified a little. Just like with web browsers, if everything is a little bit flexible in what they accept, you both improve the smoothness of the experience and create room for growth and innovation.
SAI_Peregrinus
Postel's Law is important, but it creates brittle systems. You can force them further from the ideal operating state before failure, but when they fail they tend to fail suddenly and catastrophically. I like to call it the "Hardness Principle" as opposed to the "Robustness Principle" in analogy to metallurgy.
bluGill
There is a place for both. The accept everything model made some extensions better, but it also allowed for various malware when junk was accepted.
arccy
This is so wrong, read up on https://datatracker.ietf.org/doc/html/rfc9413
The internet is ossified because middleboxes stick their noses where they shouldn't. If they just route IP packets, we could have had nice things like SCTP...
bolognafairy
Alright. See you over on the XHTML Internet. Oh, wait.
hombre_fatal
Browsers are permissive not because it's technically superior but as a concession for the end user who still wants to be able to use a poorly built website, and they're competing with browsers who will bend over backwards to render that crappy website so that they look good and your browser looks bad.
It's not a concession you want to make unless you really have to.
hinkley
If the iPhone had come out just a little bit later I think xhtml-basic would have gotten more traction. It was pretty nice to implement.
oblio
HTML is a nightmare that had to be reverse engineered as in, rebuilt with proper engineering standards in mind, several times. HTML and CSS are both quite horrible.
debugnik
XHTML still lives on in the epub spec. I kinda wish we had an "epub web".
eqvinox
All of this is understood and has been discussed to death, it's just that Arista didn't implement the agreed-best approach (RFC7606) correctly.
AdamJacobMuller
I would perhaps argue that juniper's behavior is the preferable one.
Remember the definition of this "drop the message I think is broken" not inherently "drop the broken message," it's entirely plausible that the message is fine but you have a bug which makes you THINK it's a broken message.
There is also a huge difference between considering it a broken message and a broken session, which is what Arista did.
ExoticPearTree
Arista did 2, but it also dropped the whole connection which was probably bad.
IMHO, just drop the broken attributes in the message and log them, and pass on the valid data if there's any left. If not, pretend you did not receive an UPDATE message from that particular peer.
Monitoring will catch the offending originator and people can deal with this without having to deal with any network instability.
eqvinox
In case you want to calibrate your sense of armchair-ness: you have completely missed the point that discarding an individual attribute can quite badly change the meaning of a route, and since we're talking about the DFZ here, such breakage can spread around the planet to literally every DFZ participant. The only safe thing you can do is to drop the entire route. Maybe there was a point to this being discussed at quite some length by very knowledgeable people, before 7606 became RFC ;)
(I haven't downvoted your comment, but I can see why others would — you're making very simple and definite statements about very complicated problems, and you don't seem to be aware of the complications involved. Hence: your calibration is a bit off.)
ExoticPearTree
Funny enough, I actually have a few routers with a DFZ, so I have an idea or two about how BGP works.
My point is that:
- if you drop a connection, especially one through which you announce the full routing table, it is going to create a lot of churn to your downstreams. Depending on the kind of routers they use, it can create some network instability for quite a while. And if you drop it again when you receive that malformed route, the instability continues
- removing only the malformed attribute maybe changes the way you treat traffic but you still route it. OK, you send it to maybe another interface, but no biggie
- if you’re using a DFZ setup, dropping that single route could blackhole traffic to that destination if you’re the only upstream to another router
sc68cal
I still remember the mad scramble we had to fix CVE-2023-4481 across our entire network. This class of bugs is going to be an absolute nightmare to deal with, and because of the way BGP has been designed & implemented, it is going to take a _long_ time to fix these kinds of behaviors.
mintflow
I was developping BGP feature in a telco vendor though it's decades ago.
Still think BGP is too complex and people keeping add new features and vendors keeping implement it based on RFC standard or draft.
And it seems BGP will never be deprecated so this sort of bugs will continue be found again and again...
transitorykris
There was certainly a period of time where folks like AT&T alongside Juniper and Cisco drove BGP into crazytown by way of MPLS and VPN related features. Terrifyingly complex (imo) but lucrative for some.
alecco
HGC Global Communications Limited, formerly known as Hutchison Global Communications Limited (abb. HGC), is an internet service provider of Hong Kong.
incomingpain
Our IOS XR chassis' have gotten some of these packets. Corresponding with high bgp route advertisements. No idea what equipment upstream uses tbh.
Makes me wonder if the BGP protocol is properly fuzzed. Perhaps its one of those things that everyone is scared to try to knock over given it's so important.
I suppose it would be easy to write a fuzzer for bgp but very hard to diagnose crashes?
benjojo12
(author of the post)
Yes, this is exactly what I did in the post I linked to: https://blog.benjojo.co.uk/post/bgp-path-attributes-grave-er...
incomingpain
Bravo!
This is great research!
dakiol
Is it just me or BGP is something I never learnt about until I heard about it causing issues? It seems it's essential to the internet, just like TCP/IP, but nevertheless I learnt about the latter in the university, during my career, I read many books about TCP/IP... but nothing about BGP (not in the university, not at work, not in books, nothing).
I can "play" with TCP/IP at home in dummy projects and learn more about it... but I have no idea how to "play" with BGP. In that regard, how does one learn about it at home?
bc569a80a344f9c
Buy some routers that have BGP implementations (there are some cheap ones, Mikrotik for example), or use open source implementations. The article lists bird, another very popular one is FRR (free range routing). You can trivially stand up two docker containers, stand up a BGP session between them, and - for example - propagate static routes you set up within them.
If you like guided tutorials, https://blog.ipspace.net/2023/08/bgp-labs-basic-setup/ is rather good and has been extended to somewhat advanced topics. Everything needed to follow along is free software.
remram
A good tool to try this stuff is containerlab: https://containerlab.dev/
It lets you setup multiple containers with direct connections between them in whatever topology you want. It allows you to run both Linux containers (with FRR for example) and emulated versions of popular router platforms (some of the ones mentioned in the article).
SoftTalker
OpenBSD include bgpd(8) out of the box:
DESCRIPTION
bgpd is a Border Gateway Protocol (BGP) daemon which manages the network
routing tables. Its main purpose is to exchange information concerning
"network reachability" with other BGP systems. bgpd uses the Border
Gateway Protocol, Version 4, as described in RFC 4271.petee
And a looking glass interface ready to go
zokier
At least to me one of the challenges is relating to the problems that BGP solves. You can get pretty far in network complexity before BGP (or OSPF etc) really does anything for you. What would be good scenarios one could encounter in "homelab" situation where BGP would be beneficial?
bc569a80a344f9c
There are no scenarios where BGP contained within your home lab is beneficial for anything other than learning BGP. It's the routing protocol for the Internet. Its whole point is scaling globally, and - crucially - enabling making routing decisions that aren't just based on path weights. OSPF, IS-IS, EIGRP, whatever, they are all just path finding algorithms; OSPF is quite literally Dijkstra. That's great when you want to find the shortest or fastest path to somewhere, but that's not how the Internet works: it's quite reasonable for an operator to want to take the cheapest path (in terms of money), or to take the path that avoids specific foreign countries. BGP is expressive enough to write routing policy like that. You don't need that in your homelab, unless you want to learn BGP, either because you need to for work or to further your career, or because you're curious about it.
johncolanduoni
Running a few Kubernetes nodes with a network plane like Cilium that supports using BGP to inform your router about which container IP is on which node is a simple-ish one.
null
lambdaone
Not really, unless you have thousands of routes to manage across large numbers of gateways. Otherwise, running BGP inside your homelab is just a learning tool.
qiqitori
*crickets*
mfro
DN42[1] provides a playground for routing technologies. I wouldn't recommend digging in if you don't want to dedicate a lot of time into it. As someone fairly well versed in networking, WAN routing is still confusing to me.
GNS3 is probably the easiest way to get hands on experience with any networking technologies.
ajsnigrutin
BPG is like international shipping... it has to be there for the world to function, but most people don't need to interact with it.
One way to play with it is something like this: https://www.eve-ng.net/
The other is to make a couple of virtual machines with a couple of network interfaces, make some sort of network betweeen them and then use some bgp routing deamon, eg:
https://www.nongnu.org/quagga/
etc.
ecshafer
My undergraduate networking course didn't touch BGP, my graduate networking course did touch BGP. We used a python package that acted as a simulator for different AS but I can't remember which one.
acc_297
My undergrad networks course discussed a little BGP stuff but only on the blackboard.
To experiment with BGP you could use a network simulator like what the author of this blog did. In my class we used something called gini[1] which I think my profs grad student wrote but the author apparently used gns3 which seems to be a cisco specific ns3 version. I used ns3 once and found it had a steep learning curve. The gini simulator has a more basic user interface but is probably less powerful.
[1] https://citelab.github.io/gini5/ [2] https://docs.gns3.com/docs/
altilunium
I think you need to manage a real (and large) network that's connected to global internet traffic in order to "play" with BGP. Well, you can tinker with it at home, but only by using a network simulator.
icedchai
It doesn't have to be that large. Many people have "personal" ASNs.
Check out this blog (not me, I just remember it from years back): https://blog.thelifeofkenneth.com/2017/11/creating-autonomou...
wildzzz
I worked an internship where I spent the summer setting up new equipment for a large corp that was replacing everything that AT&T had installed and managed with their own stuff. Nearly every office had their own ASN, everyone else got regular broadband or just a box of aircards depending on the number of users. I knew nothing about networks other than setting up my own consumer router at home so it was a pretty fun learning experience. I always got a smile on my face when I finally got vRouter to peer with our dummy AS in the office then we'd pack it all up and bring it out for installation over the weekend. I got offered a job to come back after I graduated but turned it down for something that paid better and was a lot more interesting. Honestly, I probably would be making more money as a network engineer now if I stuck with it.
Orochikaku
The author spoke about this story on my favourite podcast, On The Metal (of Oxide Computer Company)
azinman2
Really interesting post! Thanks for sharing
bc569a80a344f9c
You can set up local BGP routers and peer them and play with it.
Another fun thing is to log into publicly available looking glass servers. Most ISPs (including very, very, very large ones) operate routers that have their full view of the BGP routing tables. They either run web interfaces that let you query those tables (more common) or make public ssh or telnet credentials to log in with roles that have very limited access to the available commands, but have read rights to those tables.
_gmax0
Internet researchers commonly use RIPE and RouteViews.
https://www.routeviews.org/routeviews/about/ https://stat.ripe.net/docs/02.data-api/
ta1243
I've used BGP internally at my company for a decade, using AS65xxx range. At home I use BGP between the house, garage and shed, I much prefer it to OSPF.
Bluecobra
Same! At previous company I worked at we used BGP for all internal/external routing about 15 years ago despite all the poo-pooing by using BGP as an IGP. It was nice having no route redistribution and one command to monitor sessions.
l_vorenus
BGP is chill and robust, OSPF is correct and fast. Both have their own place in a network.
normie3000
Should we know what OSPF is too?
Bluecobra
You don’t need a large network to participate to BGP. You just need a /24 (IPv4) or /48 (IPv6) allocation, AS number, and a business class Internet connection that can do BGP. Might be out of reach for most hobbyists but not impossible.
icedchai
You don't even need a business class connection. You can do BGP over a tunnel to a VPS or colo.
buzer
On top of the already suggested local BGP routers you can also use https://dn42.us/ to test a bit more real-world like scenarios.
Hikikomori
Not really, you can learn it just fine with simulators and a few routers. Designing and operating BGP in a large network is another thing though.
toast0
When has BGP not been implicated in causing issues though?
The first widespread incident I found was from 1997 [1], but I didn't look too hard.
I don't think there's really a satisfying way to play with BGP as a small network. Traffic engineering is where I think the fun would be, but you've got to have lots of traffic and many connections for it to be worthwhile. Then you'd be trying to use your announcements to coax the rest of the internet to push packets through the connections you want. As well as perhaps adjusting your outgoing packets to travel the connections you prefer when possible. Sadly, nobody lets me play with their setup.
One of the ways to get a sense of emergent routing behavior is if you have hosting in many places, you'll likely see a lot of differences in routes when you start going to far off countries. If you run traceroutes (or mtr) from your home internet and your cell phone and various hosting, and if you can trace back... you'll likely see a diversity of routes. Sometimes you'll see things like going from west coast US to Brazil, where one ISP will send your packets to florida, then Brazil, and one ISP will send your packets to Spain, then Brazil, with a lot more latency.
immibis
You can play with BGP by joining https://dn42.eu/ - a fake internet with a few thousand participants who are mostly as clueless as you, and none of whom will lose millions of dollars per hour if it breaks (which is not infrequently).
moefh
I still remember when Pakistan accidentally shut down YouTube in the entire world for about 2 hours in 2008: https://www.cnet.com/culture/how-pakistan-knocked-youtube-of...
unethical_ban
TCP/IP affects every networked application and endpoint on the internet.
BGP runs the internet routing "in the background" and you only need to know it if you're an internet service provider or work in a large org managing the network. If you didn't learn network routing, you aren't going to learn BGP.
Put two or three VMs (OpenBSD has OpenBGPD daemon) onto a shared virtual switch and addresses in 172.31.255.0/24, connect the VMs. Also each of the VMs should have at least one other interface onto unique virtual switches with their own network (172.31.1.0/24, 172.31.2.0/24, etc).
Then set up BGP to redistribute connected routes.
Perenti
It appears to this reader that BGP would be a lot more stable if the various hardware vendors agreed on a standard for handling these types of things.
Is the real issue that each vendor wants lock-in, so won't standardise?
DISCLAIMER: My understanding of BGP is hollow and shallow, I am not an expert.
jiveturkey
Given the impact of such bugs, I'm surprised there isn't a consortium with an interoperability test suite. Or maybe there is, and this specific issue isn't in the test suite. In which case, I'm surprised test cases aren't generated with a fuzzer and/or machine-generated full exploration of possible packet errors. I mean, it's fine if the suite takes hours or even days to run.
I guess the author of the article here has written a fuzzer with some coverage, and has come across similar issues before. Astonishing that the vendors don't pick up on this work hungrily.
CSN3RD
Several vendors had this bug in the past https://www.kb.cert.org/vuls/id/347067
CVE-2023-4481 (Juniper) CVE-2023-38802 (FRR) CVE-2023-38283 (OpenBGPd) CVE-2023-40457 (EXOS)
Arista was not affected then.
hoseja
Has there ever been anything so byzantine in scale and accidental complexity as internet plumbing.
bhaney
> At 7AM (UTC) on Wednesday May 20th 2025
May 20th was a Tuesday, just sayin'
benjojo12
Great catch, there were like 3 mini incidents this week that I was keeping track of, so wires got crossed, will correct the post in a moment
mgaunard
Does multicast over the Internet even work?
I thought BGP was only for private networks.
bc569a80a344f9c
BGP is the routing protocol of the Internet. There effectively is no other choice of routing protocol between autonomous systems. A reasonable synonym for "Internet" is "the global BGP routing table".
BGP also doesn't use multicast, you may be thinking of OSPF on multiaccess networks. BGP uses tcp/179 unicast to the IP addresses of its configured peers.
That said, multicast works just fine over the Internet. It's not commonly used, certainly not by home users and not very often by enterprise users, and was phased out on Internet2 by 2021 (I think?), but there's absolutely nothing in principle that would make it not work.
toast0
> That said, multicast works just fine over the Internet. It's not commonly used, certainly not by home users and not very often by enterprise users, and was phased out on Internet2 by 2021 (I think?), but there's absolutely nothing in principle that would make it not work.
In principle, no. In practice, I don't think many ISPs have equipment configured to forward multicast, except for those using multicast for TV and those probably don't interconnect with others.
ta1243
Many years ago UK ISPs particpated in an MBone with BBC, ITV etc providing live broadcast
https://www.bbc.co.uk/multicast/tv/channels.shtml
Brandon Butterworths note about "why"
https://support.bbc.co.uk/multicast/why.html
Shows the growth of the backbone and CDNs:
> The Olympic audience is expected to be around 50K streams, delivering 10Gbit+ is on the limit of sensible unicast delivery.
In 2020 the BBC's internal CDN was delivering 100 times that [0] for 250k users, and 5 years later I suspect it's another order of magnitude given that iplayer does 5 million concurrent live views quite frequently [1,2]
[0] https://medium.com/bbc-product-technology/bbc-online-2020-in...
[1] https://www.bbc.co.uk/mediacentre/2024/audiences-flock-to-bb...
[2] https://www.bbc.co.uk/mediacentre/2022/england-v-iran-bbc-li...
By 2035 and TV turnoff there's no reason to believe that the infrastructure won't have been able to scale another 100 fold and handle 500 million concurrent live streams. Makes no sense to multicast out 30 different formats, to people on phones and tablets and TVs hanging off wifi. It's a very different consumer experience than a PC wired into an ISP like it was in 2007.
Bluecobra
You can definitely route multicast over the Internet via some kind of tunnel, be it stunnel, VPN, GRE. The ICE exchange uses stunnel for dev/certification multicast.
rnxrx
FWIW, 100% that BGP itself doesn't *use* multicast, but it can *propagate* multicast routing information. It's certainly technically possible to support multicast on the Internet (..thus the invention of MBGP) but in practice has been a non-starter for a whole bunch of reasons.
immibis
It's sort of correct and sort of incorrect to say it's the only possible routing protocol between autonomous systems. Since many inter-AS connections are effectively made-to-order, they could use a different protocol, but in order to participate in the global BGP mesh, it would have to have semantics similar enough to BGP. Most notably, it would have to support the concept of AS-path. However I don't think there are any universal requirements beyond that. BGP isn't a single distributed algorithm like say OSPF - a completely separate instance of BGP runs between every pair of connected ASes and they share some data, indirectly forming a global system.
ai-christianson
Anycast is pretty useful on the Internet :)
bc569a80a344f9c
Anycast is a very different beast, though. Anycast is just unicast but you announce the same IP space from multiple destinations, and the network figures out how to get a packet to the closest one. If one of those destinations fails, it just goes to the next closest one.
Unicasts, multicasts, and broadcasts all actually work differently underneath and require specific handling by network equipment. Anycast is just a special case of unicast and generally speaking network equipment is completely unaware of it.
null
AStonesThrow
In fact, IPv4 and IPv6 both have a reserved range of multicast addresses (formerly called "Class D"):
https://en.wikipedia.org/wiki/Multicast_address
There were more than a few people who spotted how disused this range had become after mbone experiments, and sometimes suggested reclaiming the range as IPv4 address space was being exhausted.
Interestingly, there are reserved multicast addresses (yes, addresses, not ports) not only for OSPF, but for many other interior routing protocols, as well as mDNS, LLMNR, and NTP. Conspicuously absent is any reservation for BGP.
FL410
BGP is very much not only for private networks - it is what the internet is built on.
Maybe you are thinking of iBGP or something like OSPF?
Hikikomori
The "Internet" is a bunch of separate networks operated by different entities. BGP is what allows them to connect to each other by exchanging routing formation.
There was something called the mbone back in the day. Nowadays you can't really send random multicast, but its very much in use by ISPs for IPTV.
patmorgan23
All traffic over the Internet is routed by routes that have been propagated through BGP. It's how adjacent networks tell each other what IPs they originate, and what networks they are connected to.
Alifatisk
No, BGP is not only for private networks. ASNs use it to exchange messages between each other.
tonetegeatinst
Unsure about multicast...my gut would say no but I'd not trust that answer if I had to bet on it.
BGP is the only way I know of that autonomous Systems can talk to each other and negotiate.
The standard approach is be liberal in what you accept and be specific in what you emit.
You could
1) Filter the broken message
2) Drop the broken message
3) Ignore the broken attributes but pass them on
4) Break with the broken attributes
To me, only 4 (Arista) is the really unacceptable behaviour. 3 (Juniper) isn't desirable but it's not a devastating behaviour.
EDIT: Actually rereading it, Arista did 2 rather than 4. I think it just closed the connection as being invalid rather than completely crash. That's arguably acceptable, but not great for the users.