What is wrong with this picture (DOS and worms)

What's wrong with this picture?

Under normal circumstances, not much. But when several machines are infected with an aggressive worm or participating in a denial of service attack when an attacker has compromised them, the switch will receive more traffic from the hosts that are connected to the 100 Mbps ports than it can transmit to the router, which also has a 100 Mbps port.

The result is that a good part of alll traffic is dropped by the switch. This doesn't matter much to the abusive hosts, but the high packet loss makes it very hard or even impossible for the other hosts to communicate over the net. We've seen this happen with the MS SQL worm in january of this year, and very likely the same will happen on august 16th when machines infected with the "Blaster" worm (who comes up with these silly names anyway?) start a distributed denial of service attack on the Windows Update website. Hopefully the impact will be mitigated by the advance warning.

So what can we do? Obviously, within our own networks we should make sure hosts and servers aren't vulnerable, not running and/or exposing vulnerable services and quickly fixing any and all infections. However, for service or hosting providers it isn't as simple, as there will invariably be customers that don't follow best practices. Since it very close to impossible to have a network without any places where traffic is funneled/aggregated, it's essential to have routers or switches that can handle the full load of all the hosts on the internal network sending at full speed and then filter this traffic or apply quality of service measures such as rate limiting or priority queuing.

This is what multilayer switches and layer 3 switches such as the Cisco 6500 series switches with a router module or Foundry, Extreme and Riverstone router/switches can do very well, but these are obviously significantly more expensive than regular switches. It should still be possible to use "dumb" aggregation switches, but only if the uplink capacity is equal or higher than the combined inputs. So a 48 port 10/100 switch that connects to a filter-capable router/switch with gigabit ethernet, could support 5 ports at 100 Mbps and the remaining 43 ports at 10 Mbps. In practice a switch with 24 or 48 100 Mbps ports and a gigabit uplink or 24 or 48 10 Mbps ports with a fast ethernet uplink will probably work ok, as it is unlikely that more than 40% or even 20% of all hosts are going to be infected at the same time, but the not uncommon practice of aggregating 24 100 Mbps ports into a 100 Mbps uplink is way too dangerous these days.

Stay tuned for more worm news soon.

Interdomain Routing Validation (IRV)

At the Network and Distributed System Security Symposium 2003 (sponsored by the NSA), a group of researchers from AT&T Labs Research (and one from Harvard) presented a new approach to increasing interdomain routing security. Unlike Secure BGP (S-BGP) and Secure Origin BGP (soBGP), this approach carefully avoids making any changes to BGP. Instead, the necessary processing is done on an external box: the Interdomain Routing Validator that implements the Interdomain Routing Validation (IVR) protocol. The IRV stays in contact with all BGP routers within the AS and holds a copy of the AS's routing policy. The idea is that IRVs from different ASes contact each other on reception of BGP update messages to check whether the update is valid.

See the paper Working Around BGP: An Incremental Approach to Improving Security and Accuracy of Interdomain Routing in the NDSS'03 proceedings for the details. It's a bit wordy at 11 two column pages (in PDF), but it does a good job of explaining some of the BGP security problems and the S-BGP approach in addition to the IRV architecture.

This isn't a bad idea per se, however, the authors fail to address some important issues. For instance, they don't discuss the fact that routers only propagate the best route over BGP, making it impossible for the IVR to get a complete view of all incoming BGP updates. They don't discuss the security and reliability implications of having a centralized service for finding the IRVs associated with each AS. Last but not least, there is no discussion of what exactly happens when invalid BGP information is discovered.

The fact that that peering policies are deemed potentiallly "secret" more than once also strikes me as odd. How exactly are ISPs going to hide this information from their BGP-speaking customers? Or anyone who knows how to use the traceroute command, for that matter?

Still, I hope they'll bring this work into the IETF or at least one of the fora where interdomain routing operation is discussed, such as NANOG or RIPE.

Jeff Doyle on the need for IPv6

In an article for the Australian Commsworld site, Juniper's Jeff Doyle explains his views on the need for IPv6. He has little patience with the scare tactics some IPv6 proponents use, but rather argues that IPv6 is simply progress and it will be cheaper to administrate in the long run.

SANS BGP security paper

The SANS (SysAdmin, Audit, Network, Security) Institute has published Is The Border Gateway Protocol Safe?. a paper (PDF) on different security aspects of BGP. Nothing groundbreaking, but detailed an a good read for people with a sysadmin background.

Worm impact on BGP

Yet another worm analysis article: Effects of Worms on Internet Routing Stability on the SecurityFocus site. This one covers Code Red, Nimda and the SQL worm. No prizes for guessing which had the most impact on the stability of the global routing infrastructure.

Yes, it's old news, unlike Cisco's latest vulnerability (which just seems like very old news) but this stuff isn't going away and we have to deal with it. Are your routers prepared for another one of these worms?

DoD to transition to IPv6 in 5 years starting october 2003

This friday the 13th (of june 2003), John Stenbit, assisten secretary of defense, announced that the US Department of Defense will start its transition to IPv6 this october. The DoD expects to be fully IPv6-capable by 2008. The reasons to switch to IPv6 are:

• better quality of service
• end-to-end security
• to keep in step with expected developments in the commercial internet

The transition is not driven by lack of IPv4 address space. However, there is no fundamental difference in QoS and security mechanisms between IPv6 and IPv4, apart from the flow label field in IPv6 for which there isn't really a use yet, so these are questionable reasons to move to IPv6. The DoD expects switching to IPv6 in the commercial internet (or at least significant parts thereof) to happen at a faster rate, so in order to keep up the DoD is taking a head start.

The DoD initiative was met with approval on the IETF discussion list, although some people remain sceptical as past announcements, such as the adoption of the ADA programming language or ISO CLNS didn't exactly pan out. Still, reading the transcipt of the briefing the DoD seems to mean business by requiring all IP-capable hard- and software procured after october first to support IPv6.