netmap: Reply to ARP requests from gateway for scan source IPs #807
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In netmap mode, the OS network stack never gets to see incoming packets unless we explicitly forward them to the host rings; hence the kernel will not be responding to ARP requests. To remove the need for static ARP entries on the gateway, respond to ARP requests from the gateway for any of the source IPs of the scan.
phillip-stephens
requested changes
Mar 5, 2024
phillip-stephens
approved these changes
Mar 5, 2024
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In netmap mode, the OS network stack never gets to see incoming packets unless we explicitly forward them to the host rings; hence the kernel will not be responding to ARP requests. To remove the need for static ARP entries on the gateway, respond to ARP requests from the gateway for any of the source IPs of the scan.
The recv thread can now submit packets for sending to send thread 0 via a zqueue. This is used to respond to ARP requests that arrive after having let loose the send threads. While still waiting for end-to-end connectivity with
--netmap-wait-ping, ARP requests are responded to by sending directly from the recv thread, just like the ICMP Echo requests.I did not see any significant netmap perf change from this at 10 GbE.
Tested on both FreeBSD and Linux. Verified to correctly respond both to arping, as well as to real ARP by deleting ARP entries from the gateway's ARP table and observing the ARP table getting repopulated as well as packets on the wire.