OSPF Summarization Question 5406zl

[Ill3st0n3]

I have 2 switches set up in a point to point ospf configuration. I am trying to summarize the network on switch 2 to switch 1. This will be a single area network and it works fine when I redistribute the connected networks. So far I have what I think would summarize this for me but it is not working yet because the destination is unreachable when trying to ping a device in a vlan on switch 2 from switch 1. Here are the configs, any help would be greatly appreciated!

ITC_LAB_SWTICH_1# show ru

Running configuration:

; J8697A Configuration Editor; Created on release #K.15.09.0012
; Ver #03:01.1f.ef:f2
hostname "ITC_LAB_SWTICH_1"
module 1 type j8702a
module 2 type j8705a
ip routing
snmp-server community "public" unrestricted
router ospf
   area backbone
   redistribute connected
   enable
   exit
vlan 1
   name "DEFAULT_VLAN"
   no untagged B21
   untagged A1-A24,B1-B20,B22-B24
   ip address dhcp-bootp
   exit
vlan 82
   name "VLAN82"
   untagged B21
   ip address 10.82.250.1 255.255.255.0
   ip ospf 10.82.250.1 area backbone
   ip ospf 10.82.250.1 authentication-key "********"
   exit
vlan 252
   name "VLAN252"
   ip address 10.252.85.1 255.255.255.0
   exit

----------------------------------------------------------------------------------------

ITC_LAB_SWITCH_2# sh ru

Running configuration:

; J8697A Configuration Editor; Created on release #K.15.09.0012
; Ver #03:01.1f.ef:f2
hostname "ITC_LAB_SWITCH_2"
module 1 type j8702a
module 2 type j8705a
ip routing
snmp-server community "public" unrestricted
router ospf
   area backbone range 10.82.0.0 255.255.0.0 type summary
   enable
   exit
vlan 1
   name "DEFAULT_VLAN"
   no untagged A1-A24,B21
   untagged B1-B20,B22-B24
   ip address dhcp-bootp
   exit
vlan 10
   name "VLAN10"
   untagged A1-A12
   ip address 10.82.10.1 255.255.255.0
   exit
vlan 20
   name "VLAN20"
   untagged A13-A24
   ip address 10.82.20.1 255.255.255.0
   exit
vlan 250
   name "VLAN250"
   untagged B21
   ip address 10.82.250.2 255.255.255.0
   ip ospf 10.82.250.2 area backbone
   ip ospf 10.82.250.2 authentication-key "********"
   exit

[LorenzoCastro]

Hello, summarization in OSPF must be performed on an ABR, a router that acts as a border between multiple areas.  You will have to add an additional area, advertise those networks in that additional area, then summarize from there.  With that said, you'll most likely not require multiple areas for this network.  Was there any specific reason why you wanted to summarize?

[Ill3st0n3]

I am in a hub and spoke network, switch 1 would be the core while switch 2 would be a districution L3 switch at a site. I am trying to reduce the size of the routing tables. Previously I was using RIP and never was able to successfully summarize with that either. We have 70+ sites, so should each site be it's own area?

[LorenzoCastro]

Simplifying routing tables is a great reason to do route summarization.  Technically, you don't need to create areas for site, but if you have multiple subnets at each site and your addressing scheme permits, it would make things easier on your eyes when viewing/troubleshooting potential routing issues.  It obviously would reduce the number of LSAs by providing summary advertisement thus keeping things a bit more quiet should you have any issues with flapping at any particular site.  With that said, multiple areas also adds complexity to your deployment and some advise against it unless you absolutely have to.  There is a great discussion on this very topic on the packet pushers podcast that our very own Paul Gear takes part in, you should check it out.  Im on my phone otherwise I'd link you, but it shouldn't be too hard to find.  I'm sure he can add some valuable insight to this thread.  

[paulgear]

Here's the podcast Lorenzo was talking about: http://packetpushers.net/show-134-ospf-design-part-1-debunking-the-multiple-area-myth/  I was there to learn, and i definitely learned much more than i contributed. :-)

The more i think about what Derek was saying, the more i believe he was right: start with a single area, and only introduce summarisation if it's necessary.  I've recently removed non-zero areas from my production network and i think it is cleaner, and as Darren pointed out, there was no issue with performance on the routers.

One thing that wasn't covered much on the Packet Pushers show is that summarisation is more for human eyes than for router CPUs.  It's your routing table, and for troubleshooting you are the one who needs to understand it, so summarisation may be a useful tool in that respect.  However, it may also make troubleshooting harder, because missing routes can be "hidden" inside a summary route that is up.  I personally found moving to a single-area network simpler because it means that i can see the full routing table on any router.  You will have to be the judge of whether this is right for you and your network.

But the short answer to your question is: if you want summarisation in OSPF, you need multiple areas, and you must summarise on the border routers (ABRs) between those areas.  There are plenty of great learning resources out there to give you more information: searching for OSPF summarisation on Youtube produces a number of useful results, and i can personally recommend Wendell Odom's CCNP ROUTE official certification guide as well.

[Ill3st0n3]

Thanks for the answers, and I am going to check out that podcast asap. The only thing I have left is to figure out the redistribution of rip into ospf or vice versa since this project is going to be moving from rip to ospf and in the future have multiple paths between networks. Any suggestions on running rip and ospf together during a migration?