We have a potential customer that is asking for us to enable MD5
authentication on a TCP connection between two BGP peers? Is this still
common practice today? Any potential problems or gotchas to keep in mind?


Sprint requires it to enable remote triggered blackhole.


lots of folks still use it yes. is it helpful? maybe? maybe not? is
this peering over a shared media (like a 10base-T hub).

You might point out that you'll be enabling this, then promptly
writing the 'secret' on a large whiteboard in your noc... because
chances are the config won't include it in rancid and ... you don't
have a place to store these securely that's not prone also to outages

also, customers wander through your NOC, so...

All that may be true, but still, the random hacker in Romania who wants in on their BGP session won't know the secret...probably.

1) that person doesn't exist
2) they need a LOT more info about what's going on anyway
3) I bet they will get a copy of the config from at least:
   a) vendor data sources
   b) ebay purchases of gear
   c) pwning a noc-worker and getting things done from there.

There are far better ways to skin this cat.

All that may be true, but still, the random hacker in Romania who wants
in on their BGP session won't know the secret...probably.

  Jon Lewis, MCP :slight_smile: | I route
  Senior Network Engineer | therefore you are
  Atlantic Net |

One thing I will do at shared peering switches is to also configure static ARP or IPv6 neighbor entries in the router for my peers. This protects against some new arrival on the switch accidentally configuring one of my peer's IP addresses on their gear and blowing up my session. That does cause some problems when a peer does maintenance that changes their MAC address, but I notice it fairly quickly.

MD5 on BGP sessions is the canonical example of a cure worse than the disease. There has been /infinitely/ more downtime caused by MD5 than the mythical attack it protects again. (This is true because anything times zero is still zero.)

It is far easier to take a router out than try to calculate the number of RSTs per second you can get through to the RE without your guesses being dropped / throttled, then waiting hours or days to watch a BGP session flap. Amazingly awesome attack, because as everyone knows BGP sessions never flap on their own, so a random session flapping every day or six will totally freak out the provider in question. And all that ignores the fact every router vendor fixed the ephemeral port selection & window size issues half a decade ago, so those "days" it takes to reset a single BGP session are actually more like months or years.

Remember, miscreants are lazy, impatient, and frequently clueless. Who would want to reset a BGP that will come back up in 30-90 seconds when you can packet an entire router off the 'Net easier, more quickly, and for longer a period?

Unfortunately, Network Engineers are lazy, impatient, and frequently clueless as well. They read something from 1906 that says "$FOO IS GOOD!!1!1!" and force every peer to subscribe to their own ideal without understanding the underlying technology or rationale.

Your network, your decision. On my network, we do not do MD5. We do more traffic than anyone and have to be in the top 10 of total eBGP peering sessions on the planet. Guess how many times we've seen anyone even attempt this attack? If you guessed more than zero, guess again.

I am fully well aware saying this in a public place means someone, probably many someones, will try it now just to prove me wrong. I still don't care. What does that tell you?


MD5 on BGP sessions is the canonical example of a cure worse than the disease. There has been /infinitely/ more downtime caused by MD5 than the mythical attack it protects again. (This is true because anything times zero is still zero.)

I don't disagree with patrick here... but 'infinitely more', is hard
to measure :slight_smile: "Most likely there have been far more lengthy outages
due to lost/changed/incorrect key material than were caused by the
problem this is meant to solve for."



Actually, when you have lot of MD5 BGP session coming up at the same
time (a connection to internet exchanges went up), you have longer
convergence time because of higher cpu load. MD5 offers no security
advantages and in some cases it causes more downtime by slowing down

I don't think md5 is that great, but I absolutely wouldn't use a clear
text password if I'm going to use anything at all.

I don't think shared seceret management is dramatically harder than any
other form of of configuration management, modula rekeying requires
coordination with a third party and is therefore hard.


I would generally say: If you are on a p2p link or control the network, then yeah, you don't need md5. If you are at a shared medium (e.g.: IX) I do recommend it there, as it will help mitigate cases where someone can hijack your session by putting your IP/ASN whatnot on the router.

The threat (Attack) never became real and we've now had enough time that even the slowest carriers are running fixed code.

- Jared

I kind of agree that there isn't much of a vector here, but I don't
agree that MD5 hurts if done correctly. Is it really that hard to
find a semi-secure place to store passwords for an entire company?
There's also the question of engineering standards. Is it an aging
practice? Probably... Is it worth spending time to update it and train
everyone not to use it? Probably not. I'll be happy when the world
realizes that it's ok to let gig-e auto-negotiate. I've never really
seen MD5 cause issues.

I have run into plenty of problems caused by MD5-related bugs.

6500/7600 can still figure the MSS incorrectly when using it. It used
to be possible for that particular box to send over-sized frames out
Ethernet ports with MD5 enabled, which of course were likely to be
dropped by the neighboring router or switching equipment (perhaps even
carrier Ethernet equipment.) Obviously that can be a chore to

Sometimes we choose to use it. Sometimes we don't.

Bugs are a different argument though. If you could call something
harmful because a single vendor codes it wrong there would be far
fewer windows users in the world. (I know it's friday, but please no
one change the subject to OS's)

I am in the camp of no MD5 in general and more specifically IX. It is a
real pain to manage MD5 and no network in my experience has ever
implemented a sustainable solution. There is no BCP that folks follow so
generally its a verbal agreement that someone in either party will
maintain the record. This works until that operator leaves the job and the
MD5 is in their email box which is no longer accessible. I would say this
is pretty common, I have inherited quite a few networks where I had to
deal with this problem. Also most common places where people store MD5's
are not in secure locations. I would argue that even though you connect
via shared medium in the case of an IX you can still use TTL.


As much as this scares me, I am going to disagree with Jared.

If another member on the IX fabric wants to do something bad, then spoofing your address and causing BGP sessions to flap is the least of your worries. I've personally configured thousand of sessions at dozens of IXes for well over a decade. I have yet to see a single case where MD5 would have been useful. OTOH, it has caused quite a bit of downtime.

There is no perfect solution, everything has issues. Past performance is no guarantee of future profits. All you can do is try your level-headed best to keep the packets flowing as quickly, reliably, and cheaply as possible. MD5 is a detriment to _all three_ of those goals.

While the quantity of peering sessions I've had is far less than
yours, once upon a time when I had tried to get MD5 on dozens of peering
sessions I learned quite a bit about those engineers and those
networks. I got to find out who couldn't do password management, who
never heard of MD5 and who had been listening to Patrick. :slight_smile: All good
input that inform what else I might want to do to protect myself from
those networks or who I wouldn't mind having a business relationship


I suppose so but BFD certainly has alot more moving parts then adding
MDF checksums to an existing control packet. I'm not saying everyone
should turn it on or off for that matter. I just don't see what the
big deal is. Most of the shops I've seen have it on because of some
long forgotten engineering standard.

My thoughts are that you should filter traffic routed directly to your BGP
speaking devices, traffic routing through a edge device and to an edge
device are treated differently. BGP session protection using a MD5 password
by itself is not securing the control plane, but it is a component of an
overall secure edge posture. For example, md5 protection, plus edge
filtering polices, plus ttl security, plus ........., make for a more
secure edge.

Also, It does not matter how many attempts compromising a BGP session
occurs, it only takes
one, so why not nail it down.


Also, It does not matter how many attempts compromising a BGP session
occurs, it only takes one, so why not nail it down.

Because downtime is a security issue too, and MD5 is more likely to contribute to downtime (either via lost password, crypto load on CPU, or other) than the problem it purports to fix. The goal of a network engineer is to move packets from A -> B. The goal of a security engineer is to keep that from happening. A business needs to weigh the cost and benefit of any given approach, and MD5 BGP auth does not come out well in the of situations.

David Barak

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