On 2/15/23 6:46 AM, Andrea Mayer wrote: > The "flavors" framework defined in RFC8986 [1] represents additional > operations that can modify or extend a subset of existing behaviors such as > SRv6 End, End.X and End.T. We report these flavors hereafter: > - Penultimate Segment Pop (PSP); > - Ultimate Segment Pop (USP); > - Ultimate Segment Decapsulation (USD). > > Depending on how the Segment Routing Header (SRH) has to be handled, an > SRv6 End* behavior can support these flavors either individually or in > combinations. > In this patch, we only consider the PSP flavor for the SRv6 End behavior. > > A PSP enabled SRv6 End behavior is used by the Source/Ingress SR node > (i.e., the one applying the SRv6 Policy) when it needs to instruct the > penultimate SR Endpoint node listed in the SID List (carried by the SRH) to > remove the SRH from the IPv6 header. > > Specifically, a PSP enabled SRv6 End behavior processes the SRH by: > i) decreasing the Segment Left (SL) from 1 to 0; > ii) copying the Last Segment IDentifier (SID) into the IPv6 Destination > Address (DA); > iii) removing (i.e., popping) the outer SRH from the extension headers > following the IPv6 header. > > It is important to note that PSP operation (steps i, ii, iii) takes place > only at a penultimate SR Segment Endpoint node (i.e., when the SL=1) and > does not happen at non-penultimate Endpoint nodes. Indeed, when a SID of > PSP flavor is processed at a non-penultimate SR Segment Endpoint node, the > PSP operation is not performed because it would not be possible to decrease > the SL from 1 to 0. > > SL=2 SL=1 SL=0 > | | | > For example, given the SRv6 policy (SID List := < X, Y, Z >): > - a PSP enabled SRv6 End behavior bound to SID "Y" will apply the PSP > operation as Segment Left (SL) is 1, corresponding to the Penultimate > Segment of the SID List; > - a PSP enabled SRv6 End behavior bound to SID "X" will *NOT* apply the > PSP operation as the Segment Left is 2. This behavior instance will > apply the "standard" End packet processing, ignoring the configured PSP > flavor at all. > > [1] - RFC8986: https://datatracker.ietf.org/doc/html/rfc8986 > > Signed-off-by: Andrea Mayer <andrea.mayer@xxxxxxxxxxx> > --- > net/ipv6/seg6_local.c | 336 +++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 333 insertions(+), 3 deletions(-) > Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
