ospf multiple area, summarization, stubs...

i've been saying this for a long time... all of this is over-engineering... it's easily relegated to network trivia, or a "we do it because we can" philosophy... but nobody wants to hear me say it... listen to these guys then...

it is no wonder my mind glazes over when these discussions come up...

http://packetpushers.net/show-134-ospf-design-part-1-debunking-the-multiple-area-myth/

and we'll have an area here and here and here, and this will be a stub, and we'll summarize there, and that needs to be nssa because it sounds cool and we get to use it in a sentence... gimme a break...

doyle ospf chap 4 case stub...

how's your stub...

add router, r5 to the topology...

spin up eigrp, add f0/0 and the loopbacks...

router eigrp 1
 network 1.0.0.0
 network 2.0.0.0
 network 172.16.0.0

m#sh run | beg eigrp
router eigrp 1
 network 172.16.0.0

before redistribution, check the lsa's on r

r#sh ip ospf data data

            OSPF Router with ID (192.168.30.1) (Process ID 10)

Area 1 database summary
  LSA Type      Count    Delete   Maxage
  Router        2        0        0      
  Network       0        0        0      
  Summary Net   2        0        0      
  Summary ASBR  1        0        0      
  Type-7 Ext    0        0        0      
    Prefixes redistributed in Type-7  0
  Opaque Link   0        0        0      
  Opaque Area   0        0        0      
  Subtotal      5        0        0      

Process 10 database summary
  LSA Type      Count    Delete   Maxage
  Router        2        0        0      
  Network       0        0        0      
  Summary Net   2        0        0      
  Summary ASBR  1        0        0      
  Type-7 Ext    0        0        0      
  Opaque Link   0        0        0      
  Opaque Area   0        0        0      
  Type-5 Ext    0        0        0      
      Prefixes redistributed in Type-5  0
  Opaque AS     0        0        0      
  Non-self      4      
  Total         5        0        0     

now redistribute...

router ospf 40
 redistribute eigrp 1 metric 1 subnets
 network 192.168.10.0 0.0.0.31 area 192.168.10.0

notice the single type 4 and 3 type 5's in the output... see table above for explanation...

area 1 is not originating external lsa's and is therefore candidate as a stub...

make area 1 a stub...

on routers r and  c add area 1 stub to each configuration...
seems insignificant for a small topology, but in a larger one, the reduction of lsa's could prove useful...

compare after the adjacency change... note the addition of a summary net (type 3) and the elimination of the single type 4 and the 3  5's...

it also now advertises a default route via the added summary lsa...

r#sh ip route | excl L | incl loop

Gateway of last resort is 192.168.30.10 to network 0.0.0.0

O*IA  0.0.0.0/0 [110/782] via 192.168.30.10, 00:07:09, Serial1/1
      192.168.10.0/27 is subnetted, 1 subnets
O IA     192.168.10.0 [110/2343] via 192.168.30.10, 00:07:09, Serial1/1
      192.168.20.0/30 is subnetted, 1 subnets
O IA     192.168.20.0 [110/1562] via 192.168.30.10, 00:07:09, Serial1/1
      192.168.30.0/24 is variably subnetted, 4 subnets, 2 masks
C        192.168.30.0/29 is directly connected, Loopback0
C        192.168.30.8/29 is directly connected, Serial1/1

they remain e2's on router g of course...

g#sh ip route

Gateway of last resort is not set

      1.0.0.0/24 is subnetted, 1 subnets
O E2     1.1.1.0 [110/1] via 192.168.10.2, 00:32:37, Serial1/3
      2.0.0.0/24 is subnetted, 1 subnets
O E2     2.2.2.0 [110/1] via 192.168.10.2, 00:32:37, Serial1/3
      172.16.0.0/24 is subnetted, 1 subnets
O E2     172.16.1.0 [110/1] via 192.168.10.2, 00:32:37, Serial1/3
      192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.10.0/27 is directly connected, Serial1/3
L        192.168.10.1/32 is directly connected, Serial1/3
      192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.20.0/30 is directly connected, Serial1/2
L        192.168.20.2/32 is directly connected, Serial1/2
      192.168.30.0/24 is variably subnetted, 2 subnets, 2 masks
O IA     192.168.30.1/32 [110/1563] via 192.168.20.1, 00:21:10, Serial1/2
O IA     192.168.30.8/29 [110/1562] via 192.168.20.1, 03:49:31, Serial1/2