When originating an AS-external-LSA [or a summary-LSA], try to use the network number as the Link State ID. If that produces a conflict, examine the two networks in conflict. One will be a subset of the other. For the less specific network, use the network number as the Link State ID and for the more specific use the network's broadcast address instead (i.e., flip all the "host" bits to 1).
Link ID ADV Router Age Seq# Checksum Tag 192.168.0.2 184.108.40.206 414 0x80000003 0x00F936 0
OSPF Router with ID (220.127.116.11) (Process ID 10)
Type-5 AS External Link States
LS age: 453 Options: (No TOS-capability, DC, Upward) LS Type: AS External Link Link State ID: 192.168.0.2 (External Network Number ) Advertising Router: 18.104.22.168 LS Seq Number: 80000003 Checksum: 0xF936 Length: 36 Network Mask: /31 Metric Type: 2 (Larger than any link state path) MTID: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0
%OSPF-4-CONFLICTING_LSAID: LSA origination prevented by LSA with same LSID but a different mask Existing Type 5 LSA: LSID 192.168.0.2/31 New Destination: 192.168.0.2/32