OSPF Routed Access

ciscogeek090 · ‎08-22-2012

Hi All,

Can anyone explain the limitations of OSPF routed access on 3560-X switch? From my understanding you can only operate a single OSPFv2 or v3 instance with 200 learned routes, is this correct? Are there any limitations with the number of areas that you can have within the single instance?

I will have 4 switches connected in a ring, each switch with a local /24 network. I would like to enable OSPFv2 on all the switches so all of the /24 networks can communicate over the shortest path and take the alternate path in the event of a link failure. Will this be possible with OSPF routed access? I might be getting confused here with EIGRP stub where you can only advertise connected routes to neighbors and not leared routes.

Benjamin Kools · ‎08-22-2012

There isn't a limitation on the number of areas, however with your small network of only 4 switches you'll be fine with leaving everything in area 0. The design you are looking for will be possible with the OSPF routed access restrictions. The below link has a little more information on OSPF Routed Access.

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8802/ps6969/ps5012/product_bulletin_c25-614546_ps10081_Products_Bulletin.html

ciscogeek090 · ‎08-22-2012

Thank you

Interestingly this document says that even though the switches support OSPF for routed access the actual number of instances and routes are not enforced. Does this mean that they will allow full OSPF fucntionality using IP base?

The plan is that 2 of the switches will be acting as the core with resilient links connecting to 2 x 3560-X switches in an office. Up to 10 offices will be connected this way over the next 12 months. I was thinking of having all of the point-to-point links in area 0 and all of the LAN networks in seperate area 1-10. Will this work or will it over complicate things?

Alessio Andreoli · ‎08-23-2012

Hi Ciscogeek,

although there are not official limitations for the number of routers in an OSPF domain there are best practices which are reccomending NO more than 90 routers per area and NO more than 1000 routers per OSPF domain. Having said this, i have personally saw a single OSPF area 0 working with almost 250 routers in it PERFECTLY.

The plan is that 2 of the switches will be acting as the core with resilient links connecting to 2 x 3560-X switches in an office. Up to 10 offices will be connected this way over the next 12 months. I was thinking of having all of the point-to-point links in area 0 and all of the LAN networks in seperate area 1-10. Will this work or will it over complicate things?

No it won't. As long as you keep your topology simple and the OSPF areas consistent you will not have any issue from it. OSPF, as IS-IS and EIGRP is a protocol that very well responds to a good planning. Just a suggestion.. Since you do not have an advanced IOS maybe it is better you care about the feature you want to enable on your infrastructure. The more homogeneus the OSPF domain is , the less issues you will have to troubleshoot !

Take Care

Alessio