On Thursday, July 30, 2015, Jason Baugher <ja...@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 <tsa...@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 <ja...@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 <j...@cymru.com > <javascript:;>> wrote: > > >> > > >> On Mon, 27 Jul 2015 19:42:46 +0530 > > >> Glen Kent <glen.k...@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 > > >> > > >
