Question

OSPF summary LSA ignored

  • 21 June 2020
  • 2 replies
  • 160 views

Hi,

I am playing with the virtual EXOS 30.4.1.2 and created a simple OSPF topology as shown in the attachment.
The issue I am seeing is that the summary LSA generated in Area1 by 3.3.3.3 (R3) and 4.4.4.4 (R4) for 15.15.15.15 (R15) is ignored by 1.1.1.1 (R1) as long as R1 is configured with a link in Area 0 WITHOUT an established adj on it.
There is no ARE0 OSPF adj. formed on R1, however the summary LSA is ignored and the route is missing from R1’s routing table.
This seems to contradicts the 16.2. section in RFC2328.

Is this the expected behaviour which can be expected on the physical hardware as well?

 

* r1.170 # show ospf int
 VLAN      IP Address         AREA ID         Flags      Cost State   Neighbors
e1-e13     172.16.17.1    /24 0.0.0.1         -rif--       5/A P2P       1
e1-e5      172.16.1.1     /24 0.0.0.0         -rif--       5/A P2P       0
loopback   1.1.1.1        /32 0.0.0.1         prif--      10/A DR        0

 

* r1.173 # show ospf lsdb lsid 15.15.15.15 detail

                LSAs for Area: 0.0.0.1

LSA Type: Summary Network
Link State Id: 15.15.15.15 (Destination Network Ip Address)
Options: None
Advertising Router: 3.3.3.3
Sequence number: 0x80000032
Checksum: 0xc20d
Age: 1741
Length: 28
Receive Interface: None
Network Mask: 255.255.255.255
Cost (TOS 0 Metric): 20

LSA Type: Summary Network
Link State Id: 15.15.15.15 (Destination Network Ip Address)
Options: None
Advertising Router: 4.4.4.4
Sequence number: 0x80000032
Checksum: 0xa427
Age: 1667
Length: 28
Receive Interface: None
Network Mask: 255.255.255.255
Cost (TOS 0 Metric): 20

 

* r1.175 # show iproute 15.15.15.15/32
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration

Origin(Ori): (ap) Auto-peering, (b) BlackHole, (be) EBGP, (bg) BGP, (bi) IBGP,

 

 

 

 

 


2 replies

Hi,

The diagram doesn’t show the physical topology.
The p2p interface is there because 1.1.1.1 is not directly connected to 3.3.3.3 and 4.4.4.4 but to another switch in area 0.
There is no connectivity issue from 1.1.1.1 to both ABRs in area 0.

* e1.62 # show  iproute 3.3.3.3/32
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
#oa  3.3.3.3/32         172.16.17.13    20   UG-D---um--f- e1-e13     16d:5h:0m:44s

 

* e1.63 # show  iproute 4.4.4.4/32
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
#oa  4.4.4.4/32         172.16.17.13    20   UG-D---um--f- e1-e13     16d:5h:1m:11s

 

* e1.74 # show iproute 15.15.15.15/32
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
 

* e1.67 # show ospf lsdb lsid 15.15.15.15 detail

                LSAs for Area: 0.0.0.1

LSA Type: Summary Network
Link State Id: 15.15.15.15 (Destination Network Ip Address)
Options: None
Advertising Router: 3.3.3.3
Sequence number: 0x80000340
Checksum: 0x9d21
Age: 1245
Length: 28
Receive Interface: None
Network Mask: 255.255.255.255
Cost (TOS 0 Metric): 20

LSA Type: Summary Network
Link State Id: 15.15.15.15 (Destination Network Ip Address)
Options: None
Advertising Router: 4.4.4.4
Sequence number: 0x80000340
Checksum: 0x7f3b
Age: 1172
Length: 28
Receive Interface: None
Network Mask: 255.255.255.255
Cost (TOS 0 Metric): 20

 

* e1.68 # show ospf lsdb lsid 3.3.3.3 detail

                LSAs for Area: 0.0.0.1

LSA Type: Router
Link State Id: 3.3.3.3 (Originator Router Id)
Options: None
Advertising Router: 3.3.3.3
Sequence number: 0x80000346
Checksum: 0x8d8e
Age: 1334
Length: 84
Receive Interface: None
Area Border Router

 

* e1.69 # show ospf lsdb lsid 4.4.4.4  detail

                LSAs for Area: 0.0.0.1

LSA Type: Router
Link State Id: 4.4.4.4 (Originator Router Id)
Options: None
Advertising Router: 4.4.4.4
Sequence number: 0x80000342
Checksum: 0x90b
Age: 1336
Length: 84
Receive Interface: None
Area Border Router

 

* e1.72 # ping count 1 3.3.3.3 from 1.1.1.1
Ping(ICMP) 3.3.3.3: 1 packets, 8 data bytes, interval 1 second(s).
16 bytes from 3.3.3.3: icmp_seq=0 ttl=63 time=5.043 ms

--- 3.3.3.3 ping statistics ---
1 packets transmitted, 1 packets received, 0% loss
round-trip min/avg/max = 5/5/5 ms

 

* e1.73 # ping count 1 4.4.4.4 from 1.1.1.1
Ping(ICMP) 4.4.4.4: 1 packets, 8 data bytes, interval 1 second(s).
16 bytes from 4.4.4.4: icmp_seq=0 ttl=63 time=1.112 ms

--- 4.4.4.4 ping statistics ---
1 packets transmitted, 1 packets received, 0% loss
round-trip min/avg/max = 1/1/1 ms

 

 

Once the interface in AREA0 on 1.1.1.1 is removed, the summary LSA is taken into consideration and the route shows up in the routing table.

* e1.77 # configure ospf delete vlan e1-e5


* e1.78 # show iproute 15.15.15.15/32
Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
#or  15.15.15.15/32     172.16.17.13    30   UG-D---um--f- e1-e13     0d:0h:0m:4s

 

 

 

 

 

Userlevel 5

If 3.3.3.3,4.4.4.4 and 1.1.1.1 are all in AREA 0, why do you have a p2p interface? shouldn’t that be a Broadcast so that adjacencies can be formed to both nexthops?  RtMgr will not install a route passed from OSPF in the routing table if the next hop is not reachable.

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