On 8/11/2011 10:19 AM, Jason Duerstock wrote: > On Thu, Aug 11, 2011 at 8:57 AM, CJ <cjinfant...@gmail.com> wrote: > >> Hey all, >> Is there any reason to run IS-IS over OSPF in the SP core? Currently, we >> are running IS-IS but we are redesigning our core and now would be a good >> time to switch. I would like to switch to OSPF, mostly because of >> familiarity with OSPF over IS-IS. >> What does everyone think? >> >> -- >> CJ >> >> http://convergingontheedge.com <http://www.convergingontheedge.com> >> > Granted, we're not a service provider, so we operate on a different scale > here, but one interesting trick that can be done with ISIS (at least on > Cisco) is this: > > router a > ----------- > router isis > advertise passive-only > > interface loopback0 > ip address 10.1.1.1 255.255.255.255 > > interface vlan2 > ip unnumbered loopback0 > ip router isis > isis network point-to-point > > > router b > ----------- > (copy router isis definition from router a) > > interface loopback0 > ip address 10.1.1.2 255.255.255.255 > > (copy vlan2 definition from router a) > > ----------- > > This removes the associated headaches with /30s or /31s in having to keep > track of their allocation, as well as having them clog the your routing > table. > > -waits for replies stating why this is a bad idea- > > Now, if I could just get isis-per-vrf-instance support on the Catalyst 6500. > > Jason One of my favorite features in IS-IS is the ability to set the overload bit during maintenance. The effect is the router on which you set it isn't seen by any other devices in the topology as a transit path, but you can still reach the router itself. I'm not as familiar with OSPF so I'm unsure if there is a similar feature, but I thought it was exclusive to IS-IS. Being able to easily limit the IGP size via the above technique is also a great benefit. You can basically get away with just your loopbacks.
-Vinny
