OSPF Question. I'm Confused.

[RoDDy]

Hi Guys,

I was on a thread looking at a query someone had and responded but based on how the thread is going I'm wondering if what i said was wrong?

See link below.

http://www.networking-forum.com/viewtopic.php?f=33&t=48062

[icecream-guy]

Hi Guys,

I was on a thread looking at a query someone had and responded but based on how the thread is going I'm wondering if what i said was wrong?

See link below.

http://www.networking-forum.com/viewtopic.php?f=33&t=48062

eww that site.....



All non-zero areas need to be somehow connected to area zero.

[RoDDy]

Hi Guys,

I was on a thread looking at a query someone had and responded but based on how the thread is going I'm wondering if what i said was wrong?

See link below.

http://www.networking-forum.com/viewtopic.php?f=33&t=48062

eww that site.....



All non-zero areas need to be somehow connected to area zero.

Agreed, but the other guy was saying they need to be in area 0. All i was trying to explain is that since the other routers are directly connected to interfaces on Router4, which is in area 0, then the OSPF will work with the other routers which are in different areas. Router4 will be the ABR.

[icecream-guy]

Hi Guys,

I was on a thread looking at a query someone had and responded but based on how the thread is going I'm wondering if what i said was wrong?

See link below.

http://www.networking-forum.com/viewtopic.php?f=33&t=48062

eww that site.....



All non-zero areas need to be somehow connected to area zero.

Agreed, but the other guy was saying they need to be in area 0. All i was trying to explain is that since the other routers are directly connected to interfaces on Router4, which is in area 0, then the OSPF will work with the other routers which are in different areas. Router4 will be the ABR.

they would need to have at least one interface in area zero, the routers don't need to be completely in area zero, e.g. all router interfaces in area zero.  Assuming were doing normal OSPF without the use of virtual links or super backbones.

[Nerm]

I agree with ristau5741. My understanding is that OSPF area's cannot be daisy chained so to speak.

[LynK]

virtual links are where it is at!!

[srg]

Please post the question in whole here as well, we have no idea how long an external link will be accessible.

[SimonV]

We have no idea how long an external link will be accessible.

It could very well go down for a few days 

[deanwebb]

I think the question in the OP is why doesn't this work:

R4
router ospf 1
network 10.0.0 0.0.0.255 area 0
network 20.0.0 0.0.0.255 area 1

R5
router ospf 2
network 20.0.0 0.0.0.255 area 1
network 30.0.0 0.0.0.255 area 2

R6
router ospf 3
network 30.0.0 0.0.0.255 area 2
network 40.0.0 0.0.0.255 area 3

[that1guy15]

Looks like a use of terms is confusing everyone.  First whatever teacher gave that topology should be fired. Unless he/she was trying to trick the students. Horrible topology for entry level. OSPF is already confusing enough to learn.

Area 0 is whats known as the backbone area. All non-backbone areas must have at least one ABR router which connects that area to the backbone area. To be an ABR the router must have at least one interface with an adjacency to another router in the backbone area and at least one interface connecting to the non-backbone area. Or more simply put one interface in area 0 and one in another area. If an area is unable to connect an ABR to the backbone a shim-link must be used to transit the non-backbone area.

Without a ABR connected to the backbone, LSAs will still propagate across the area but will not propagate between areas.

[NetworkGroover]

Looks like a use of terms is confusing everyone.  First whatever teacher gave that topology should be fired. Unless he/she was trying to trick the students. Horrible topology for entry level. OSPF is already confusing enough to learn.

Area 0 is whats known as the backbone area. All non-backbone areas must have at least one ABR router which connects that area to the backbone area. To be an ABR the router must have at least one interface with an adjacency to another router in the backbone area and at least one interface connecting to the non-backbone area. Or more simply put one interface in area 0 and one in another area. If an area is unable to connect an ABR to the backbone a shim-link must be used to transit the non-backbone area.

Without a ABR connected to the backbone, LSAs will still propagate across the area but will not propagate between areas.

+1, and shim-link = OSPF Virtual Link

[that1guy15]

Ah good catch AspiringNetworker! Mis-use of terms.

Shim-link serves another purpose. Virtual-link is what I meant.

Blah and I call my self a CCIE....

[wintermute000]

That's a sham link not a shim link LOL but hey you wouldn't know it at all if you weren't a ccie
I've only ever seen a single occasion where a carrier allowed OSPF as a MPLS-VPN PE-CE protocol and even then there was no backdoor link scenario to require a sham-link

[NetworkGroover]

Lol exactly - I don't even know what a sham-link is....

I just thought he was using slang for the official term so for the OP I listed the official term... wasn't meant to look like I was correcting him   

And that1guy, dude, my buffer has gotten so small, I'd be amazed if you can recall everything you've learned in your journey off the top of your head... I can't even remember specific VXLAN feature-to-platform support... 

[that1guy15]

Nah its cool dude, I never mind being corrected on a mistake.

Sham-links connect MPLS PE to PE routers together so LSAs that traverse the MPLS core look like intra-area instead of inter-area LSA. Basically stretching the area across the MPLS cloud. This is also know as the super-backbone. This is now where the vrf-lite command comes in, but that is a whole other set of worms. Fuck you P bit!!

Its weird what sticks and what dosent. and trust me there is a ton that is not sticking after I passed.