Mirja, I believe draft-ietf-bess-mvpn-expl-track-13 addresses your issues. I have expanded the Security Considerations section per your suggestions, which IMO are all very reasonable.
Please let me know whether this is satisfactory. Thanks. Eric On 11/26/2018 9:03 AM, Mirja Kuehlewind (IETF) wrote: > Hi Eric, > > thanks for your detailed reply. Please see below. > >> Am 15.11.2018 um 19:07 schrieb Eric Rosen <ero...@juniper.net>: >> >> On 10/24/2018 8:28 AM, Mirja Kühlewind wrote: >>> --------------------------------------------------------------------- >>> DISCUSS: >>> ---------------------------------------------------------------------- >>> >>> In section 9 (security considerations): >>> Thanks for discussing network load here! However, I find this sentence a bit >>> unsatisfactory: >>> „The specification of counter-measures for this problem is outside the >>> scope >>> of this document.“ >>> Isn’t there any easy way to make some more recommendations for counter >>> measures >>> that could be discussed here? E.g. implement some rate limiting or >>> filtering. >>> Or only accept LIR-PF request from preconfigured hosts (given that LIR-PF >>> support must anyway be pre-configured)? I’m not an expert on this topic and >>> therefore don’t know if any of such recommendations make sense, however, I >>> would quickly like to discuss if it is potentially possible to say more than >>> what’s current said. Thanks! >> These particular suggestions don't really work in this context. >> >> - The set of Provider Edge routers (PEs) that attach to a given VPN is >> always auto-discovered, never pre-configured. That's an important part >> of the L3VPN value proposition. There are already mechanisms in place >> to ensure that the S-PMSI A-D route gets sent only to the proper set of >> egress PEs. Also, a properly functioning egress PE will only respond >> with a Leaf A-D route if it has already auto-discovered the ingress PE. >> (You might want to question the security of the L3VPN mechanisms, but >> that would certainly be outside the scope of this document .) >> >> - Rate limiting the generation of Leaf A-D routes wouldn't work, because >> the problem is not that one PE generates too many, but that too many PEs >> may generate them. Rate limiting the processing of received Leaf A-D >> routes is also problematic. In normal operation, you might correctly >> get a whole bunch of them in quick succession, and if you don't process >> them in a timely manner, the customers will see a high multicast "join >> latency". >> >> In the particular sort of attack mentioned in the Security >> Considerations section, an ingress PE originates an S-PMSI A-D route >> with LIR-pF clear, but somehow the bit gets set before the route is >> received by the egress PEs. As Alvaro has suggested, if an attacker >> can modify the control messages, quite a bit of havoc can result, and >> the particular attack under discussion is just one of many that can >> occur if the control plane is not secure. I can certainly put in a >> reference to RFCS 6192 and 7454 (as Alvaro suggests), if you think that >> is helpful. Properly protecting the control plane should prevent this >> kind of attack. > Okay, then I would simply suggest to say this ("Properly protecting the > control plane should prevent this kind of attack“) instead of just calling it > out of scope. > >> In the event such an attack occurs, mitigating it is unfortunately not >> very straightforward. The ingress node can take note of the fact that >> it is getting Leaf A-D routes with LIR-pF set, in response to an S-PMSI >> A-D route with LIR-pF clear. Withdrawing the S-PMSI A-D route could put >> a stop to the attack. However, there are a few problems with this: >> >> - Under normal operation, there are some race conditions that may cause >> the ingress node to think it is being attacked, when in fact it is not. >> >> - If some egress nodes have a bug that causes them to set LIR-pF when it >> should be clear, withdrawing the S-PMSI A-D route will stop the flow of >> multicast data traffic to all the egress nodes, causing an unnecessary >> customer-visible disruption. >> >> - The same situation that caused the S-PMSI A-D route to be originated >> in the first place will still exist after the S-PMSI A-D route is >> withdrawn, so the route will just be re-originated. >> >> In other words, any action that would ameliorate the effects of this >> sort of attack would have a negative effect during normal operation. >> Therefore it is really better to rely on security mechanisms that >> protect the control plane generally, rather than having a mechanism that >> is focused on this one particular type of attack. > This suggest that there is no good counter measure which would be more > appropriate to say instead of calling it out of scope. I think it could even > be helpful to add some of your explanation above to the security > consideration section (instead of leaving this as an exercise to the reader). > >> We could say that if an ingress PE receives a Leaf A-D route with LIR-pF >> set, and that route is a response to an S-PMSI A-D route that did not >> have LIR-pF set, the event MUST be logged. This would generate some >> noise in the log during normal operation, but could provide at least a >> hint that an attack is occurring. > I think this would be a good recommendation. I guess it actually does have to > be a MUST, or you could say something like MUST be logged by default but can > be configured differently if the protection mechanism used for the control > plan is monitored. As I said, I’m really no expert here and you need to > decide if that makes any sense though. > > Mirja > > >> What do you think? >> >>> ---------------------------------------------------------------------- >>> COMMENT: >>> ---------------------------------------------------------------------- >>> >>> Some other minor comments: >>> 1) section 2: „Use of this flag in the PTA carried by other route types >>> is outside >>> the scope of this document. Use of this flag in the PTA carried by >>> an S-PMSI A-D routes whose NLRI does not contain a wildcard is >>> outside the scope of this document.“ >>> Maybe you also want to say something like „The flag SHOULD be ignored in >>> these cases.“..? >> Agreed. >> >>> 2) section 3 >>> s/The result (if any) is the match for tracking“/The result (if any) is the >>> “match for tracking“/ >>> (missing quotes) >> Fixed in the next revision. _______________________________________________ BESS mailing list BESS@ietf.org https://www.ietf.org/mailman/listinfo/bess