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How is the originating AREA ID of a type-3 summary lsa is fetched? This is the AREA ID displayed as in "show ip ospf lsdb".

The AREA-ID field in OSPF header is the area to which the OSPF packet is destined right?, then how is the originating AREA ID information is retained for type-3 LSAs when flood across areas ?

  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Feb 21 '18 at 17:45
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I think I got confused by the output on lsdb on ABR. It will display LSDB for both areas , but for a moment I forgot that it is ABR and was wondering how summary lsa for network in neighboring area(area 2) was displayed in area 0 router still displaying it as area 2. Later realized that is it ABR and LSDB being displayed in the show output is combined LSDB of both the areas:- Answer: Area ID of type-3 lsa for a network in one area(say area 1) is not retained when generated for another area(say area 0). output:-

topology:-

       10.10.10.0/24      20.20.20.0/24      30.30.30.0/24      40.40.40.0/24
  rtr1----------------rtr2----------------rtr3--------------rtr4(vrf4)------------rtr5
     <===area-1 =====>   <==============area-0=============>         <==area-2===>


switch# show ip ospf lsdb vrf vrf_4 <<<< here vrf_4 can be imagined as a physical router - ABR between area0 and area 2

   OSPF Router with ID (4.4.4.4) (Process ID 1 VRF vrf_4)

            Router Link States(0.0.0.0)
LSID            ADV Router      Age       Seq#       Checksum       Link count
2.2.2.2         2.2.2.2         825       0x80000005 0x000015ac     1
3.3.3.3         3.3.3.3         469       0x80000005 0x00007479     2
4.4.4.4         4.4.4.4         314       0x80000003 0x00000b68     1

            Network Link States(0.0.0.0)
LSID            ADV Router      Age       Seq#       Checksum
30.30.30.4      4.4.4.4         473       0x80000001 0x0000d3fb
20.20.20.2      2.2.2.2         831       0x80000001 0x000029d6

            Summary Network Link States(0.0.0.0)
LSID            ADV Router      Age       Seq#       Checksum
10.10.10.0      2.2.2.2         854       0x80000001 0x0000cf66 <<<< displayed as area 0 only. Originally this network is in area 1
40.40.40.0      4.4.4.4         309       0x80000001 0x0000577c

            Router Link States(0.0.0.2)
LSID            ADV Router      Age       Seq#       Checksum       Link count
4.4.4.4         4.4.4.4         307       0x80000002 0x000071c5     1
5.5.5.5         5.5.5.5         308       0x80000002 0x000030fe     1

            Network Link States(0.0.0.2)
LSID            ADV Router      Age       Seq#       Checksum  
40.40.40.5      5.5.5.5         313       0x80000001 0x0000960e

            Summary Network Link States(0.0.0.2) <<<< was confused on this
LSID            ADV Router      Age       Seq#       Checksum
20.20.20.0      4.4.4.4         309       0x80000001 0x000034da
30.30.30.0      4.4.4.4         309       0x80000001 0x0000c031
10.10.10.0      4.4.4.4         309       0x80000001 0x0000a784
switch#
  • You should accept your answer so that the question doesn't keep popping up forever, looking for an answer. – Ron Maupin Dec 25 '17 at 5:46

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