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> 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> wrote: >> >> On Mon, 27 Jul 2015 19:42:46 +0530 >> Glen Kent <glen.k...@gmail.com> 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 >>
