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Hi All,

A Bit of a strange one today. I was working through the excellent Vol I v5 OSPF Labs today and came accross a very strange thing happening to me in Task 6.3. Basically I was seeing DR Pre-emption taking place on the Broadcast VLAN 146. Here is how I had my Lab configured:

• I Configured R6 to have an OSPF Priority of 255 for VLANs 67 & 146 (Priority configured on both sub-interfaces).
  
• I Configured R1 to have an OSPF Priority of 250 for VLAN 146.
• I left R4 with the default config (I know your solutions guide says to make this priority 0, but at this stage I hadn't done this!).
• When I had re-configured these priorities, I just sent a clear IP OSPF PROCESS command to ALL devices so they would re-converge etc.
• When the routers had formed all their adjacancies again, R6 was as we would expect the DR for VLANs 67 & 146.
• R1 Was the BDR for VLAN 146.

This was all fine, and was as I expected everything to be, however, I continued on with the exercise and shut down FA0/0 on R6 to let R1 become DR. Sure enough R1 became the DR for VLAN 146 after it was detected to be Down. R4 became DR (Since I hadn't removed R4's priority earlier), this too was fine and as expected.

Now came the strange part - Once I did a no shut on R6 FA0/0, and then ran the show ip ospf int brief command it showed R6 to be the DR on both VLANs 67 & 146?? I also issued the show ip ospf interface command and it too reported the state of R6 FA0/0 to be DR on both VLANs....?? I tried this a number of times to make sure I wasnt seeing things or imagining things and sure enough each time I witnessed the strange results???

This to me looked like DR Pre-emption which we all know doesnt exist

I Would appreciate anyone's feedback on this, and just wondering if anyone else has ever come across something like this before?

Thanks,

Ian.

Hi All,

A Bit of a strange one today. I was working through the excellent Vol I v5 OSPF Labs today and came accross a very strange thing happening to me in Task 6.3. Basically I was seeing DR Pre-emption taking place on the Broadcast VLAN 146. Here is how I had my Lab configured:

 

• I Configured R6 to have an OSPF Priority of 255 for VLANs 67 & 146 (Priority configured on both sub-interfaces).
  
• I Configured R1 to have an OSPF Priority of 250 for VLAN 146.
• I left R4 with the default config (I know your solutions guide says to make this priority 0, but at this stage I hadn't done this!).
• When I had re-configured these priorities, I just sent a clear IP OSPF PROCESS command to ALL devices so they would re-converge etc.
• When the routers had formed all their adjacancies again, R6 was as we would expect the DR for VLANs 67 & 146.
• R1 Was the BDR for VLAN 146.

 

This was all fine, and was as I expected everything to be, however, I continued on with the exercise and shut down FA0/0 on R6 to let R1 become DR. Sure enough R1 became the DR for VLAN 146 after it was detected to be Down. R4 became DR (Since I hadn't removed R4's priority earlier), this too was fine and as expected.

Now came the strange part - Once I did a no shut on R6 FA0/0, and then ran the show ip ospf int brief command it showed R6 to be the DR on both VLANs 67 & 146?? I also issued the show ip ospf interface command and it too reported the state of R6 FA0/0 to be DR on both VLANs....?? I tried this a number of times to make sure I wasnt seeing things or imagining things and sure enough each time I witnessed the strange results???

This to me looked like DR Pre-emption which we all know doesnt exist

I Would appreciate anyone's feedback on this, and just wondering if anyone else has ever come across something like this before?

Thanks,

Ian.

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Thanks for the reply Brian,

I am doing some Labs again today and I have recreated this task exactly as I did on Saturday, as I wanted to run the debug as you mentioned. However, this time the results were exactly as expected??? When I brought the R6 interface back up it became DROther as it should do.

Only difference between today and Saturday is that I am on RS Rack 10 today, where as I was on RS Rack 16 on Saturday!

There wouldnt be a difference of IOS would there? I even ran that task a couple of times to make sure it really was behaving strange!

Best Regards,

Ian.