On 8/11/2011 10:19 AM, Jason Duerstock wrote:
On Thu, Aug 11, 2011 at 8:57 AM, CJ <cjinfantino@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