While doing integration work with OpenDaylight (ODL) LISP Flow Mapping (LFM), I tested mapping removal handling. When a mapping is removed from LFM, its "subscribers" (xTRs which asked for the mapping – if any) are sent a Solicit-Map-Request (SMR) LISP control message, to ask for the mapping again and refresh their map cache. The resulting SMR-invoked Map-Request message sent by the xTR is handled by LFM in a special way: if the mapping lookup results in a negative mapping, it sets the time-to-live (TTL) value of the reply to 0, in order to "delete" the mapping from the xTR. Until this point everything works as expected.

However, the resulting negative mapping with TTL 0 stays in the VPP EID table as a remote EID entry indefinitely:

vat# lisp_eid_table_dump
{{ EID type ls_index ttl authoritative key_id key}}
{{ [1] 10.11.12.100/32 local 0 0 0 1 admin}}
{{ [1] 10.11.12.2/32 remote 1 86400 0 0}}
{{ [1] 10.11.12.101/32 remote action: 1 0 0 0}}