OSPF -vs- ISIS

Wed Jun 22 15:42:46 UTC 2005

On Tue, Jun 21, 2005 at 03:16:06PM +0100, Richard Dumoulin wrote:
> Hi Eric, what's the reason for migrating to ISIS?

There are currently a few projects that we're doing which prompted us to 
take a look at how we're doing routing, both IGP and EGP.  We're altering our 
border connectivity by spreading our multiple commodity Internet and 
Internet2 peers across multiple routers that connect into our core at 
multiple locations.  As a result, we're likely to bring iBGP into our core 
and, clearly, this is going to alter our IGP setup.  We're also looking into 
MPLS layer 2 VPNs to solve certain traffic classification issues (e.g. 
limiting I2 access, allowing "guest wireless" etc), which also means that we'd 
likely need to make modifications to our IGP/EGP setup.  Though we filter 
OSPF multicast traffic, we wanted to add in MD5 passwords to our neighbors.  
We're deploying IPv6 within our campus, so we needed to look for an IGP to 
support this.  Since we're going to have to make changes, some significant, to
our IGP setup (currently multi-area OSPF) no matter what, we felt it made 
sense to review our options.  

It looks like IS-IS and OSPF are pretty much the same in terms of functionality.
IS-IS, though, looks like it handles IPv6 networks more efficiently, its area 
scheme seems to match a little more to our topology, and the "security' 
element (i.e. you can't inject packets) of the adjacencies seems interesting.  
Also, as I said, we're likely going to move to an iBGP-based core, which seems 
to run parrallel to what service providers are doing, so I have to admit that 
"follow the leader" also played into the decision as larger ISP seem to be 
doing the iBGP/IS-IS combo.

Eric :)