Stub vs. Totally stub

cdad2000

Hey everybody,
Just wondering which of these area types excepts default routes? Or is that NSSA.

kafifi13

If i'm not mistaken it should be Totally stubby.

nice343

a stub area accepts LSA types 1,2,3

total stub acceps LSA 1,2.

Which means with a stub area a default route is generated to the ABR External routes /redistributed routes (type 5 LSA) will not appear in the routing table. but can be reached because of the default route


With a total stub, both external routes and inter area routes get replaced with a single default route.

Which means when you sit infront of a router which has routes passing through a total stub area, the routing table will only show a deault route. Both Inter-area routes and redistributed routes are replaced with a single default route

bmauro

So like nice said - all stub areas have default routes - since when you issue the "area # stub" or the "area # stub no-summary" the ABR automatically generates a default route to the stub area.

Now - if you meant "Just wondering which of these area types excepts SUMMARY routes" or type 3 LSA, then that would be a regular stub and NSSA.

darkuser

here's a nice link ....

http://www.cisco.com/warp/public/104/8.html

cdad2000

Thanks for all your help.

dtimmerm

If I'm correct?

For Stub area: LSA 1,2,3,4 + 1 default route for all external summary links
For Totally stub area: only LSA 1,2 + default route

I thought that the default route shows up as a LSA type 3 in OSPF database.

Maybe somebody can put some output of a stub router and a totally stub area.


For Stub area, the LSA 4 seems to be useless as there is a default route.

Somebody comments on this?

Mrock4

3 router topology here....Router5.....AREA 1 STUB.....Router2.......AREA 0......Router1.


This is R5's output as a regular stub area. I created some loopback's on Router1 so you could see the network 172.16.x.x. Just threw this up, didn't feel like summarizing.




Gateway of last resort is 192.168.1.17 to network 0.0.0.0

172.16.0.0/32 is subnetted, 3 subnets
O IA 172.16.1.1 [110/129] via 192.168.1.17, 00:00:00, Serial2/0
O IA 172.16.3.1 [110/129] via 192.168.1.17, 00:00:00, Serial2/0
O IA 172.16.2.1 [110/129] via 192.168.1.17, 00:00:00, Serial2/0
192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
O IA 192.168.1.0/30 [110/128] via 192.168.1.17, 00:00:00, Serial2/0
C 192.168.1.17/32 is directly connected, Serial2/0
C 192.168.1.16/30 is directly connected, Serial2/0
O*IA 0.0.0.0/0 [110/65] via 192.168.1.17, 00:00:00, Serial2/0
R5#

You can see the default route here, also on R5:

OSPF Router with ID (100.1.1.1) (Process ID 100)

Router Link States (Area 1)

Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 158 0x80000007 0x006CC8 2 <

---

Old loopback interface

Summary Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 160 0x80000001 0x0075C0
172.16.1.1 2.2.2.2 160 0x80000002 0x005BDA
172.16.2.1 2.2.2.2 160 0x80000002 0x0050E4
172.16.3.1 2.2.2.2 160 0x80000002 0x0045EE
192.168.1.0 2.2.2.2 160 0x80000002 0x001D71
R5#


So let's make it a totally stubby area using "area 1 stub no-summary"


Gateway of last resort is 192.168.1.17 to network 0.0.0.0

192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.17/32 is directly connected, Serial2/0
C 192.168.1.16/30 is directly connected, Serial2/0
O*IA 0.0.0.0/0 [110/65] via 192.168.1.17, 00:00:01, Serial2/0
R5#

All the summary routes (Type 3) are gone...but...


OSPF Router with ID (100.1.1.1) (Process ID 100)

Router Link States (Area 1)

Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 340 0x80000007 0x006CC8 2

Summary Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 24 0x80000002 0x0073C1
R5#


You can see the default route still hasn't changed. The only difference is the Type 3 summary's are now gone.


And as far as the Type 4 goes for a stub area, the Type 4 will be sent from an area containing an ASBR, to let the rest of the network know how to reach that external network, whereas a type 3 will generally point you to a node within your OSPF network. Very small difference really.

Hope to have helped.

dtimmerm

yes, thanks for the effort!


I think if there would be an ASBR it would be also advertised (as type 4) and appear as a summary link state in the OSPF database. Sometimes they say for stub area: only LSA 1,2,3 and in other documents they say LSA 1,2,3,4. This is what's confusing me.


About "totally stub area". The only question that left is how the default route is advertised from the ABR to the others. I suppose as a type 3 LSA (which should be the only exception) to 0.6 if there's a DR or to 0.5 if there's no DR

kryolla

NSSA does not inject a default route you have to tell it to.

dtimmerm

kryolla wrote:

NSSA does not inject a default route you have to tell it to.

I think if there would be an ASBR it would be also advertised (as type 4) and appear ....

I mean an ASBR in some other area. I'm talking about a stub area and not a NSSA