On Wed, Mar 21, 2018 at 9:27 AM, Sri Gundavelli (sgundave) <sgund...@cisco.com> wrote: > FYI. This is the notes that Carlos captured. Thank you Carlos!! > > We are also waiting for Lyle to share his notes. Please review and > comment, if you see any mistakes. >
With regards to SR encapsulation: "this is using IP-in-IP as default. Why not using UDP encapsulation?" There is some rationale for UDP encapsulation here to maximize compatibility with the network and potentially intermediate nodes like firewalls. For example, in the performance numbers that Kalyani posted, the TPS for SR over IPIP routing was lower than other encapsulations. The reason for this is that the particular NIC (ixgbe) is not parsing over IPIP or using flow label to get a good hash for RSS. This is symptomatic of network devices that don't provide as good support for protocols outside of TCP and UDP. There are likely routers that would not be able to provide flow specific ECMP for similar reasons. There was a comment in dmm meeting that ECMP for IPIP was expected to by solved by using flow label in the hash. This is a great idea, but unfortunately there is significant resistance to using flow label for this purpose since it is not guaranteed to be persistent for a flow and that can cause problems for stateful devices like firewalls. UDP encapsulation is the typical answer to network protocol compatibility. Several UDP encapsulation techniques have been defined as well as some foo over UDP to run existing encapsulations over UDP (e.g. MPLS/UDP, GRE/UDP). draft-ietf-rtgwg-dt-encap gives a nice overview of considerations for UDP encap protocols. If a UDP encapsulation is considered for use with SR, I would suggest GUE is an option. GUE has some unique features: - It's extensible (both common extensions are defined and allows custom extensions per use case) - It's generic (can encapsulate any IP protocol) - It allows directly encapsulating IPv4 and IPv6 in UDP (to minimize encapsulation overhead) - It allows encapsulation of extension headers The last point may be of particular interest to SR. SR over IPIP might be more precarious compared to other encapsulations since it introduces two "atypical" (i.e. not TCP or UDP) protocols. GUE could be used to normalize SR packets to look like UDP to the network. This might look something like: IP|UDP|GUE|Routing_hdr|IP|payload The UDP and GUE header are effectively treated as routing shim at each segment hop so SR is processed as without regard to the encapsulation. To intermediate nodes these packets looks like any other UDP packet so there's no compatibility issue. Tom _______________________________________________ dmm mailing list dmm@ietf.org https://www.ietf.org/mailman/listinfo/dmm
