Hi I work for a vendor selling and IKE/IPsec solution.
In the last few months, we've heard a troubling complaint from some of our customers. They say that some ISPs have begun to drop IP fragments. While specific ISPs were not named, most of the issues seem to be in south-east Asia. One customer has speculated that this has something to do with preparing to deploy CGNs. According to draft-ietf-behave-lsn-requirements, CGNs MUST comply with the NAT requirements for UDP as in RFC 4787, and that RFC says in section 11 that NAT devices MUST support fragments. So these routers are not compliant, but that doesn't help our customers much. Most traffic on the Internet is either TCP or small-packet UDP. The IKE protocol (both versions) has the rather rare distinction of having large UDP packets. These are packets #5 and #6 in IKEv1 Main Mode, or the IKE_AUTH packets in IKEv2, especially when using certificate authentication. For now, the customers managed to "fix" the ISP with an angry phone call. That got them into an exception list where fragments are not dropped. One had to change ISPs for that. While this can work for a while, it won't work when the carrier doing the dropping is not the one that the customer has a business relationship with, but another one downstream. Trying to think up ways to deal with this, I can think of some: * Get all ISPs to stop dropping fragments. This would be great, but as the saying goes, you are so not in charge. * Find ways of making the packets smaller: move to PSK, fiddle with trust anchors so that only one cert is needed, avoid sending CRLs, hash-and-URL, etc. These are not always successful, and often require more configuration than we would like. * Build a fragmentation layer within IKE, so IKE messages are broken into several packets that get reassembled at the destination. This is the path taken by one of our competitors [1]. This means that IKE has segmentation in addition to other TCP-like features such as retransmission. * Use IKE over TCP. Looking at the IANA registry ([2]) TCP port 500 is already allocated to "ISAKMP". We have had IKE running over TCP for several years for remote access clients. This was done because remote access clients connect from behind some very dodgy NAT devices, and some of those do drop fragments. Getting this behavior at the ISP is novel. Have others on this list run into this issue? Yoav [1] http://www.cisco.com/en/US/docs/ios/sec_secure_connectivity/configuration/guide/sec_fragment_ike_pack.html [2] http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml _______________________________________________ IPsec mailing list IPsec@ietf.org https://www.ietf.org/mailman/listinfo/ipsec
