UDP clamped on service provider links

Fri Jul 31 03:51:32 UTC 2015

On Thursday, July 30, 2015, Jason Baugher <jason at thebaughers.com> wrote:

> Several months ago we had an issue with a customer whose IPSEC tunnels we
> manage. One of the tunnels dropped, and after troubleshooting we were able
> to prove that only udp/500 was being blocked in one direction for one
> specific source and destination IP. Level3 resolved the issue, but claimed
> it was due to a "mis-configured NNI" between themselves and Charter. Seems
> odd that an NNI mis-config could cause something that specific, doesn't it?
>
>
NNI is a peering link.

Peering links blow up during ddos since they act as a narrow funnel of
traffic between networks.

So NNI is exactly where udp ddos filters show up most, at least that is my
guess

> On Thu, Jul 30, 2015 at 9:44 PM, Tom Sands <tsands at rackspace.com
> <javascript:;>> wrote:
>
> > We have similar problems with UDP 500 and being able to keep IPSEC
> tunnels
> > up over Level3. It happens quite a bit when there are no signs of TCP or
> > ICMP packet loss.
> >
> > Sent from my iPhone
> >
> > > On Jul 30, 2015, at 9:14 PM, Jason Baugher <jason at thebaughers.com
> <javascript:;>>
> > wrote:
> > >
> > > To bring this discussion to specifics, we've been fighting an issue
> where
> > > our customers are experiencing poor audio quality on SIP calls. The
> only
> > > carrier between our customers and the hosted VoIP provider is Level3.
> > From
> > > multiple wiresharks, it appears that a certain percentage of UDP
> packets
> > -
> > > in this case RTP - are getting lost in the Level3 network somewhere.
> > We've
> > > got a ticket open with Level3, but haven't gotten far yet. Has anyone
> > else
> > > seen Level3 or other carriers rate-limiting UDP and breaking these
> > > legitimate services?
> > >
> > >> On Thu, Jul 30, 2015 at 3:45 PM, John Kristoff <jtk at cymru.com
> <javascript:;>> wrote:
> > >>
> > >> On Mon, 27 Jul 2015 19:42:46 +0530
> > >> Glen Kent <glen.kent at gmail.com <javascript:;>> wrote:
> > >>
> > >>> Is it true that UDP is often subjected to stiffer rate limits than
> > >>> TCP?
> > >>
> > >> Yes, although I'm not sure how widespread this is in most, if even
> many
> > >> networks. Probably not very widely deployed today, but restrictions
> and
> > >> limitations only seem to expand rather than recede.
> > >>
> > >> I've done this, and not just for UDP, in a university environment.  I
> > >> implemented this at time the Slammer worm came out on all the ingress
> > >> interfaces of user-facing subnets. This was meant as a more general
> > >> solution to "capacity collapse" rather than strictly as security
> issue,
> > >> because we were also struggling with capacity filling apps like
> Napster
> > >> at the time, but Slammer was the tipping point.  To summarize what we
> > >> did for aggregate rates from host subnets (these were generally 100
> Mb/s
> > >> IPv4 /24-/25 LANs):
> > >>
> > >>  ICMP:  2 Mb/s
> > >>   UDP: 10 Mb/s
> > >> MCAST: 10 Mb/s (separate UDP group)
> > >>  IGMP:  2 Mb/s
> > >> IPSEC: 10 Mb/s (esp - can't ensure flow control of crypto traffic)
> > >>   GRE: 10 Mb/s
> > >> Other: 10 Mb/s for everything else except for TCP
> > >>
> > >> If traffic was staying local within the campus network, limits did not
> > >> apply.  There were no limits for TCP traffic.  We generally did not
> > >> apply limits to well defined and generally well managed server
> subnets.
> > >> We were aware that certain measurement tools might produce misleading
> > >> results, a trade-off we were willing to accept.
> > >>
> > >> As far as I could tell, the limits generally worked well and helped
> > >> minimize Slammer and more general problems.  If ISPs could implement a
> > >> similar mechanism, I think this could be a reasonable approach today
> > >> still.  Perhaps more necessary than ever before, but a big part of the
> > >> problem is that the networks where you'd really want to see this sort
> > >> of thing implemented, won't do it.
> > >>
> > >>> Is there a reason why this is often done so? Is this because UDP
> > >>> is stateless and any script kiddie could launch a DOS attack with a
> > >>> UDP stream?
> > >>
> > >> State, some form of sender verification and that it and most other
> > >> commonly used protocols besides TCP do not generally react to implicit
> > >> congestion signals (drops usually).
> > >>
> > >>> Given the state of affairs these days how difficult is it going to be
> > >>> for somebody to launch a DOS attack with some other protocol?
> > >>
> > >> There has been ICMP-based attacks and there are, at least in theory if
> > >> not common in practice, others such as IGMP-based attacks.  There have
> > >> been numerous DoS (single D) attacks with TCP-based services precisely
> > >> because of weaknesses or difficulties in managing unexpected TCP
> > >> session behavior.  The potential sending capacity of even a small set
> > >> of hosts from around the globe, UDP, TCP or other protocol, could
> > >> easily overwhelm many points of aggregation.  All it takes is for an
> > >> attacker to coerce that a sufficient subset of hosts to send the
> > >> packets.
> > >>
> > >> John
> > >>
> >
>