Hello @SJ K ,
looking at your network diagram I assume that the redistribute static is configured on switch02.
As a result of this Switch02:
a) Advertises an LSA type 5 with originator ID = its own OSPF RID
b) it sets the E flag bit in its Router LSA to signal it has became an ASBR injecting external routes into the OSPF domain
Both information the LSA type 5 and the new version of switch02 Router LSA are flloded out each interface in OSPF domain ( not only in area 0 also out of standard non backbone areas if any, this is trued only for the LSA type 5, the router LSA is confined to a single area)
Now, coming to your questions:
1) >> 1) when switch1 receive external ospf 16.0/24 advertisement on ge-0/0/1 from switch 2 - does it fwd the external advertisement towards R4 ge-0/1 ?
Yes switch01 will flood out unchanged both the LSA type 5 and the new version or Router LSA of switch02 on the direct link to R4. To be noted R4 can receive it also on the broadcast link with switch01 and switch02.
Actually on a broadacst link new LSAs are sent first to the OSPF DR on the segment designated router using mulitcast address 224.0.0.6 and this is done by switch02, then the DR for the segment will re-advertise it to all OSPF routers on segment using destination multicast address 224.0.5.
You can check who is OSPF DR using show ip ospf interface on all routers. Also a BDR is elected.
The highest OSPF RID wins unless there is a device with an higher OSPF priority.
2) >> is the default external ospf advertisement metric type = 2 ?
Yes, O E2 is the default externa route type in this case the seed metric in the LSA is not directly summed to the internal metric to reach the ASBR node.
3) >> 3) does that means on R4 , the selected route to 192.168.16.0/24 is through switch1 ge-0/0/2 and switch2 ge-0/0/4 ? since the metric will be the same for external ospf advertisement type 2 ?
No, even if O E2 does not sum up the seed metric to the internal metric to the ASBR the best path to ASBR node is still preferred so R4 will choice a path directly to switch02 the ASBR node for the prefix.
>> any idea why show route on R4 is showing the selected route for 192.168.16.0 is through switch2 ge-0/0/4 ?
This is correct because that path provides the best path to ASBR that originated the LSA type 5. Even if O E2 a best path is selected using the best path to the ASBR.
What you see is normal and expcted
On R4
issue
show ip ospf border-routers
to see that the best path to switch02 OSPF RID is via switch02:gi0/0/4
use
show ip ospf database external 192.168.16.0
to see all the contents of the LSA type 5.
Hope to help
Giuseppe
