[FROG] Isn't ospf ban an ABR to flood lsa3 to a non-backbone area?

[chan alfie]

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?
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