ISIS verses OSPF as IGP in MPLS using TE

[MTolliver]

The network will be supporting VPN, VoIP, FRR, TE, QoS, etc. Between ISI and OSPF, which one is easier to configure, support, and troubleshoot, etc.? Which is more scalable?

[Harold Ritter]

The debate on whether to use OSPF or ISIS in a large SP core has been going on forever. I think personally that the first criteria should be what protocol are your staff most familiar with.

From experience, I can tell you that the largest SPs in the world are currently using ISIS. The reasons for that though is not only because of ISIS being more scalable but also for historical reason. When these very large IP backbones were first deployed, OSPF was not around so the requirement for a link state protocol made it simple, the only solution was ISIS.

One thing I like about ISIS is that because of its TLV implementation, it is very easy to extend and therefore always seems to be the first routing protocol to support new routed protocols or technologies (MPLS TE, IPv6, Multi Topology, etc).

I would say that currently both protocols support MPLS TE equally well.

Here's a good presentation discussing OSPF vs ISIS.

It was presented by Dave Katz at NANOG 19 in June 2000:

http://www.nanog.org/mtg-0006/katz.html

Hope this helps,

[romccallum]

Harry, I would need to totally agree with you here. I am an ISIS fan but the MPLS network that I had to design HAD to run OSPF. This decision was made due to staff familiarity and supportability.

WRT ISIS being more flexible and usually first to market new technologies such as TE/IPv6 etc for some reason or another Cisco seem to implementing LDP synchornisation first in OSPF. Why??

[Harold Ritter]

My comment about ISIS being first to market was protocol specific. Since IGP-LDP synchronization is IOS specific, the ISIS greater flexibility didn't come into play here. I suspect that this feature being first available with ospf is probably customer driven.

Hope this helps,

[oettls]

Robert,

do you have any information when LDP synchronization for OSPF is planned to be integrated in IOS ?

thanks

Stefan

[romccallum]

The new command is likely to be:

mpls ldp session protection [for ] [duration ]

Default duration is infinite, but it can configured between 30 and 4294967 seconds.

Available on 12K, 7200 and 7500 from 12.0(30)S – due December 2004.

Available on 10K, 7600, 7300 from 12.2 Rls7 – not until mid to late 2005.

Will work initially with OSPF only.

LDP-IGP Synchronization addresses the same problem as LDP Session Protection.

For 12.0(30)S, OSPF only.

SO the answer is apparently NOW as 12.0(30)S is out now.

[oettls]

Robert,

thanks for your detailed answer.

cheers,

Stefan