SV: IGP protocol

Gustav Ulander gustav.ulander at
Thu Nov 15 02:05:59 UTC 2018

Hello all.

We also run a small network (sub 50 PEs)
It looks pretty similar to Baldurs except we run IS-IS instead of OSPF.
IPV4 only in the global table with VPNV4 and VPNv6 services running on top of it.
We do run a separate OBM network to handle management without being dependent on service infrastructure for management.
Only real difference we notice is that Cisco seem to roll out service provider features and knobs for IS-IS first and then eventually for OSPF.
Good or bad is the question.


Från: NANOG <nanog-bounces at> För Baldur Norddahl
Skickat: den 15 november 2018 02:51
Till: nanog at
Ämne: Re: IGP protocol

We run a MPLS enabled network with internet in a VRF. Management is in VRF default (no VRF). The IGP is OSPFv2. IPv6 is handled by the L3VPN functionality of MPLS. So is IPv4.

The IPv4 that is controlled by OSPF is totally separate from everything except management and could really be any protocol. For a small network like ours, with everything in area 0 and VRF/L3VPN to handle dual stack, there is zero differences between is-is and OSPF. The IPv4 management network is not any more reachable than the is-is protocol. There are no raw IPv6 packets on the wire and no need for the IGP to handle IPv6.

Also not true that the management network is the last thing to boot. In contrary, everything else depends on that being ready first. And that would also be true if we used is-is.

We chose OSPF because it was one less protocol to learn and one less ethernet type on the wire. But really it could be toss a coin.



ons. 14. nov. 2018 14.55 skrev James Bensley <jwbensley at<mailto:jwbensley at>>:
On Tue, 13 Nov 2018 at 12:09, Saku Ytti <saku at<mailto:saku at>> wrote:
> On Tue, 13 Nov 2018 at 12:37, Mark Tinka <mark.tinka at<mailto:mark.tinka at>> wrote:
> > Main reasons:
> >     - Doesn't run over IP.
> Why is this upside? I've seen on two platforms (7600, MX) ISIS punted
> on routers running ISIS without interface having ISIS.  With no
> ability to limit it, so any connected interface can DoS device with
> trivial pps rate, if ISIS is being ran.

I guess the OPs original question wasn't clear enough because, I think
most people are talking about IS-IS vs OSPF2/3 from a theoretical
protocol perspective, and you're talking from a practical vendor
implementation perspective.

From a purely theoretical perspective I see IS-IS not running over IP
as an advantage too. No mater what routes I inject into my IGP, IS-IS
won't stop working. I may totally fsck my IP reachability but IS-IS
will still work, which means that when I fix the issue, service should
be restored quite quickly. Several networks I've seen place management
in a VRF / L3 VPN, which means that by the time you have remote
management access, everything else is already working, it's like the
last thing to come up when there's been a problem. I like the
"management in the IGP + IS-IS" design.

However, in reality the vendor implementation blows the protocol
design out of the water. You need to consider both when evaluating a
new IGP. Cisco nearly implemented a handy feature with
prefix-suppression, whereby in IOS for OSPF only one would prevent
p-t-p links being advertised into the IGP database. But they didn't
implement this for IS-IS. Then in IOS-XR they removed this feature
from OSPF and implemented it for IS-IS ?!?! So yeah, vendors
implementations are just as important and the theoretical potential of
the protocol.

Oh yeah, forgot to answer the original question. For a greenfield
deployment I'd be happy with either OSPFv3 or IS-IS as long as it's
well designed I don't see much between them, it would come down to
vendor support then.

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