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This patch fixes intermittent DHCPv6/link-local punt loops caused by a startup race in IPv6 link-local discovery. LL discovery ran in configureVppUplinkInterface() before Linux had brought the tap UP, so LL was intermittently missing. Without LL /128 in punt table, punted link-local packets matched fe80::/10 (ip6-link-local DPO), got redirected back to per-interface LL FIB, and looped until VPP recursion guard dropped them. - Add configureIPv6LinkLocal() and call it from runVpp() after configureLinuxTap() (LinkSetUp) and before InterfaceAdminUp(). - Poll for tap LL with bounded retries after tap UP; if not found, return an error so runVpp() terminates VPP. - Program LL-specific state in configureIPv6LinkLocal(): * punt-table LL /128 route * LL address on uplink in VPP * ND proxy for LL - Remove old LL handling from the previous setup path. Signed-off-by: Aritra Basu <aritrbas@cisco.com>
sknat
approved these changes
Mar 2, 2026
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This PR fixes an intermittent IPv6 startup issue where DHCPv6 traffic to the node link-local address can enter a punt loop, preventing global IPv6 from being acquired.
RCA
LL discovery previously ran during
configureVppUplinkInterface(), before Linux tapNETDEV_UP. In intermittent cases, no LL was discovered in time, so the LL/128route was not installed in the punt table.For punted LL traffic (e.g. DHCPv6 UDP/546), lookup in the punt table then matched the built-in
fe80::/10 -> ip6-link-localpath, which redirected traffic back to the per-interface LL FIB and created a receive/punt/redirect loop until recursion drop.Fix
configureIPv6LinkLocal()invpp-manager/vpp_runner.go.runVpp()afterconfigureLinuxTap()and beforeInterfaceAdminUp().terminateVpp()path./128route in punt table