OSPF DR and BDR questions

[xyyz]

I'm doin' the OSPF labs right now... And I have some confusion with DR and BDR elections. Iot says that the DR and BRD are determined by priority which has a default of 1. It then says, in the case of a tie, the router ID, which is the highest router ID... Which is an interface IP address.

Now, this is the way my routers are configured:

Vista - e0,192.168.100.246/28 lo0,192.168.31.22/32
SJ1 - e0,192.168.100.248/28 lo0,192.168.31.11/32
SJ2 - e0,192.168.100.247/28 lo0,192.168.31.33/32

OSPF is running... I assume, since I aint too clear on the notation... On the 192.168.100.240/28 network (network 192.168.100.240 0.0.0.15 area 0)

However when you look at the DR and BDR, it seems that the loopback addresses and not the e0 addresses are the router ID's. What gives? 192.168.100 is higher in number than 192.168.3x

 

[ScottMac]

Loopback addresses are used because they can't flap or go down (unless they are taken down or the router dies).

A flapping OSPF interface is a very bad thing.

FWIW

Scott

 

[xyyz]

alright... i got it...

"cisco routers use the highest loopback IP addresses as the OSPF Router ID. In the absence of a loopback inerface, the router uses the highest IP address among its active interfaces, which might force a router to change router IDs if an interface goes down...."

and then it goes on to say exactly what you said.

thanks

 

[xyyz]

oh one more thing...

how can you enable synchronous logging on telnetted connections?

it would be nice if i had a console server, but i dont. so i'm using the extra ethernet interfaces on my routers as a makeshit console. i need to pull the OSPF debug output from a router, but I can't?

did the following:

line vty 0 4
logging synchronous level all

but this doesn't seem to do anything

 

[bgroff]

Originally posted by: xyyz
oh one more thing...

how can you enable synchronous logging on telnetted connections?

it would be nice if i had a console server, but i dont. so i'm using the extra ethernet interfaces on my routers as a makeshit console. i need to pull the OSPF debug output from a router, but I can't?

did the following:

line vty 0 4
logging synchronous level all

but this doesn't seem to do anything

router#term mon

 

[xyyz]

router#term mon

very very very sweet... thanks.


wait... actually....

now that i turned it on... how do i turn it off?

no term mon doesn't seem to work

 

[bgroff]

Originally posted by: xyyz

router#term mon

very very very sweet... thanks.


wait... actually....

now that i turned it on... how do i turn it off?

no term mon doesn't seem to work

term no mon

Its tricky like that...

 

[xyyz]

alright i'm having some issues with this lab.

when SJ2 is disabled... you get the election process running and vista is elected DR and SJ1 BDR. now, when you bring SJ2 back up... it stays that SJ2 should become the DR again.... but it's not. what's the deal?

SanJose1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.33 1 FULL/DROTHER 00:00:18 192.168.1.3 Ethernet0
192.168.31.22 1 FULL/BDR 00:00:19 192.168.1.2 Ethernet0


SanJose2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.11 1 FULL/DR 00:00:19 192.168.1.1 Ethernet0
192.168.31.22 1 FULL/BDR 00:00:15 192.168.1.2 Ethernet0


Vista#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.33 1 FULL/DROTHER 00:00:18 192.168.1.3 Ethernet0
192.168.31.11 1 FULL/DR 00:00:18 192.168.1.1 Ethernet0

 

[bgroff]

Originally posted by: xyyz
alright i'm having some issues with this lab.

when SJ2 is disabled... you get the election process running and vista is elected DR and SJ1 BDR. now, when you bring SJ2 back up... it stays that SJ2 should become the DR again.... but it's not. what's the deal?

SanJose1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.33 1 FULL/DROTHER 00:00:18 192.168.1.3 Ethernet0
192.168.31.22 1 FULL/BDR 00:00:19 192.168.1.2 Ethernet0


SanJose2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.11 1 FULL/DR 00:00:19 192.168.1.1 Ethernet0
192.168.31.22 1 FULL/BDR 00:00:15 192.168.1.2 Ethernet0


Vista#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
192.168.31.33 1 FULL/DROTHER 00:00:18 192.168.1.3 Ethernet0
192.168.31.11 1 FULL/DR 00:00:18 192.168.1.1 Ethernet0

Nope, sorry. That's not the way OSPF works. It will not preempt a DR or BDR, even if it has a better priority. Who ever is king at the time stays king. Now ISIS on the other hand... It will force an election and recapture the DR crown...

 

[xyyz]

Nope, sorry. That's not the way OSPF works. It will not preempt a DR or BDR, even if it has a better priority. Who ever is king at the time stays king. Now ISIS on the other hand... It will force an election and recapture the DR crown...

this is what the lab book said:

In the debug output look for a statement about remembnering the "old DR." Unless SJ1 and Vista are powered off, the will remember that SJ2 was the old DR. When SJ2 come sback online, these routers will allow SJ2 to reassume it's role as DR:

here's the next lab question:

Bring SJ2 back online, and observe thenew election process.

SJ2 will assume its former fole as DR. Who is elected BDR? Why?

i remember what you said in what i've read... it said that the DR BDR's were concrete even if another router with a higher router ID came into the network...