Automated cherry pick of #5942: Update maximum number of buckets in an OVS group message #5997: Use 65000 MTU upper bound for interfaces in encap mode #6141
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) The current implementation limits the maximum number of buckets in an OVS group add/insert_bucket message to 800. This constraint is based on the fact that each bucket has 3 actions, such as `set_field:0xa0a0007->reg0`, `set_field:0x50/0xffff->reg4`, and `resubmit(,EndpointDNAT)`. However, an update in antrea-io#5205 introduced a new action, `set_field:0x4000000/0x4000000->reg4`, for remote Endpoints, making it impossible to accommodate 800 buckets with 4 actions in an OVS group add/insert_bucket message. To overcome the limitation, we set the maximum number of buckets to 700, considering the worst-case scenario where each bucket includes all available actions. For example, a bucket with all available actions, which is for a remote non-hostNetwork IPv6 Service Endpoint like this: `set_field:0xa0a0007->xxreg0`, `set_field:0x50/0xffff->reg4`, `set_field:0x100000/0x100000->reg4`, and `resubmit(,EndpointDNAT)`. The size of such bucket is 88 bytes, and the header size of an OVS group message is 24 bytes. According to https://opennetworking.org/wp-content/uploads/2014/10/openflow-switch-v1.5.1.pdf, the max size of an Openflow 1.5 message is 65535 bytes, as a result, a message can have a maximum of 744 buckets, calculated with (65535-24)/88, using the largest possible size. Signed-off-by: Hongliang Liu <[email protected]>
OVS configures the MTU for tunnel ports to 65000. In some cases (e.g., Kind clusters), the MTU of the transport interface can be larger than that, and so can be the calculated MTU of antrea-gw0 and of Pod interfaces. When this happens, packets can be dropped. To handle this edge case (real clusters are unlikely to use that kind of MTU), we set an upper bound of 65000 for the calculated MTU. Note that setting the tunnel port's MTU to 65535, or even to the calculated MTU, is not an option, as it may not work on all systems. An alternative would be to find the MTU for the tunnel interface dynamically and use that as an upper bound, rather than rely on this hardcoded constant (65000). However, that constant has remained unchanged for 7 years, and finding the MTU dynamically would require re-organizing the Agent initialization code, as we currently caclulate the MTU before creating the OVS tunnel port. So the current solution seems lower risk. Even if the constant is changed in OVS, it should not have any real impact on Antrea. Fixes antrea-io#5940 Signed-off-by: Antonin Bas <[email protected]>
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Cherry pick of #5942 #5997 on release-1.13.
#5942: Update maximum number of buckets in an OVS group message
#5997: Use 65000 MTU upper bound for interfaces in encap mode
For details on the cherry pick process, see the cherry pick requests page.