hi community, I got some confused of ospf lsa3. topology: h1 -- r1 --a12-- r2 --a0-- r3 --a34-- r4 -- h4 | | +---a23 ---+ I am using mininet to emulate the above environment. Here are the topo desc: area 12: r1(intf:r1r2) and r2(intf:r2r1) , connected network: 10.0.12.0/30 area 0: r2(intf:r20r30) and r3(intf:r30r20), connected network: 10.0.23.0/30 area 23: r2(intf:r2r3) and r3(intf:r3r2), connected network: 10.0.23.4/30 area 34: r3(intf:r3r4) and r4(intf:r4r3), connected network: 10.0.34.0/30 r1 has a stub net: 10.0.1.0/254, connected to a host, h1 r4 has a stub net: 10.0.4.0/254, connected to a host, h4 my question is: why r2/r3 generated lsa3 and advertise on area 23, isn't it prohibited ABR to flood lsa3 to non-backbone area? r2 ``` # show ip ospf database Summary Link States (Area 0.0.0.23) Link ID ADV Router Age Seq# CkSum Route 10.0.0.1 10.0.0.2 448 0x80000001 0xdc5f 10.0.0.1/32 10.0.0.1 10.0.0.3 449 0x80000001 0x3bf5 10.0.0.1/32 10.0.0.2 10.0.0.2 498 0x80000001 0x6ed6 10.0.0.2/32 10.0.0.2 10.0.0.3 449 0x80000001 0xcc6d 10.0.0.2/32 10.0.0.3 10.0.0.2 448 0x80000001 0xc871 10.0.0.3/32 10.0.0.3 10.0.0.3 498 0x80000001 0x5ee4 10.0.0.3/32 10.0.0.4 10.0.0.2 128 0x80000001 0x230c 10.0.0.4/32 10.0.0.4 10.0.0.3 129 0x80000001 0xb87f 10.0.0.4/32 10.0.1.0 10.0.0.2 448 0x80000001 0x40f1 10.0.1.0/24 10.0.1.0 10.0.0.3 449 0x80000001 0x9e88 10.0.1.0/24 10.0.4.0 10.0.0.2 128 0x80000001 0x83a1 10.0.4.0/24 10.0.4.0 10.0.0.3 129 0x80000001 0x1915 10.0.4.0/24 10.0.12.0 10.0.0.2 498 0x80000001 0x50e3 10.0.12.0/30 10.0.12.0 10.0.0.3 449 0x80000001 0xae7a 10.0.12.0/30 10.0.23.0 10.0.0.2 498 0x80000001 0xd652 10.0.23.0/30 10.0.23.0 10.0.0.3 498 0x80000001 0xd057 10.0.23.0/30 10.0.34.0 10.0.0.2 448 0x80000001 0xc152 10.0.34.0/30 10.0.34.0 10.0.0.3 498 0x80000001 0x57c5 10.0.34.0/30 ``` any idea?