ospfd: NSSA area should not exchange Type-4 LSAs in DD
Problem Statement:
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OSPF Peer gets stuck in EXSTART with ARISTA Device.
Root Cause:
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First peer is form with Arista device in normal area and then
the area type is changed to NSSA. Due to this Type-4 and Type-5
LSAs advertised by Arista router is still present in
the OSPF DB. While DD exchange the Type-5 LSAs are omitted but
the Type-4 LSAs are not omitted due to which Arista device gets
stuck in EXSTART and it keeps moving between EXCHANGE And EXSTART.
Fix:
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When the area is NSSA, we should not send Type-4 LSAs in DD
exchange packet.