Can ISIS be an alternative to a hybrid network without hierarchy?

[aavelar]

In a hybrid network without hierarchy (physical or logical), with point-to-point connections, what would be the best routing protocol?
It is a network composed of approximately 200 network assets.
There is a need for automatic contingency.
The network owner wants to implement MPLS for service segmentation, so an IGP is necessary, with that in mind, we have the EIGRP, OSPF and ISIS option.
In this network, it is not possible to segment in areas, because the capillarity is very large, and one OSPF area can not be transit to another.
Is ISIS a good choice considering the network totally flat? Remembering that 100% of the connections are point-to-point.

The links are fiber and radio wireless. Sometimes, with radio, we can see a lot of flaps up/down.

Someone can help?

I've attached a drawing to illustrate the type of network we're talking about.

[chrihussey]

Hello,

Although there are some differences, ISIS and OSPF are "area" based protocols. The only significant difference between OSPF and ISIS is that ISIS does not have the area 0 or backbone limitation. In other words, in OSPF in order to get from one area to another you must transit the area 0 backbone. In ISIS, you can easily move between areas without having to first traverse a backbone area. So there is a distinct advantage there.

The network topology you've provided is certainly complex and intertwined. In all cases a single ISIS or OSPF area would work, and considering ISIS' functionality, you could possibly make a few areas.  EIGRP would work just as well. So here's a quick rundown of the protocols:

EIGRP: Less CPU intensive and faster than ISIS or OSPF. Would operate as a single autonomous system. Cisco proprietary and vendor specific. Would be issues with non Cisco devices or environments.

OSPF: We know about the Area 0 limitation, however a single area (0) could suffice. Slower convergence and more CPU intensive. Standard protocol, so not vendor specific. Probably most widely used protocol.

ISIS: Potential to set up multiple areas. Same CPU and convergence as OSPF. A standard protocol, but not widely used. Used mostly in large ISP network environments. Not always an available option on some platforms or with other vendors. So there may be some limitations.

So, all three protocols have their pros and cons, and the complexity of the topology is a challenging, but doable in all cases.

Hope this is of some help.

[aavelar]

Thank you chrihussey.

     Are you say that both protocol (ISIS and OSPF) on a single area will work even considering 200 routers and a lot of flaps on radio links on this kind of topology?

    The fact of connection being configured with point-to-point, can it help?

[chrihussey]

In a stable network it would work. I missed your earlier indication about the flapping and it being a regular event in the radio environment. I could see how that may cause issues with the constant changes and flooding of link state updates. A valid concern.

That being said, perhaps it may be a good idea to break up your network into 4 quadrants (so 50 routers in each) and run single instances of ISIS or OSPF in each and then BGP peer between each quadrant. This way any flapping would be isolated to a smaller areat and have less of an impact on the rest of the network. Of course the allocation of IP space would be key in simplifying the BGP advertisements between AS. You could also influence and optimize the routing a lot easier.

Just a thought and may be a good way to go.

Hope that makes sense.