Subject: [rbridge] Choice of routing protocols

From: erik.nordmark at sun.com (Erik Nordmark)
Date: Fri Feb 4 11:58:55 2005

Below is an excerpt from emails between myself and Bob Hinden that tries
to capture some issues around the choice of routing protocol.
Hopefully this can stimulate further discussion on this topic.

    Erik

-------- Original Message --------
Subject: Re: Late agenda item?:  ipvlx charter
Date: Mon, 31 Jan 2005 10:24:35 -0800
From: Erik Nordmark <[email-masked]>
To: Bob Hinden <[email-masked]>

Bob Hinden wrote:

> I also wonder if we want to consider OSPF for this.  The IETF owns all 
> the IPR and can produce derivative standards, where the situation with 
> ISIS is very different (e.g., OSI owns the basic protocol). It's going 
> to be difficult for an L2 bridge implementor to figure out and 
> understand which collection of IETF and OSI specs to use.  Also, if I 
> remember correctly, ISIS still requires manual configuration of 20 byte 
> OSI NSAP addresses.  This would be a pretty odd thing for a L2 bridge.

AFAIK it is only the 6-byte MAC address that is the 'system ID' in
IS-IS. One would probably need to fill in some dummy value for the AFI
and area, but this can be done without any manual config since each box
is assumed to have a factory assigned unique MAC address.

OSPF is a bit harder in fact, since (even with the IPv6 pieces in
OSPFv3) the OSPF router ID is a 4 byte number, and there isn't any
existing numbering space which could be used to create factory assigned
globally unique 32 bit numbers.

While in principle OSPF is interesting and should be explored, there are
some additional items (in addition to the router ID assignment) which
makes using OSPF harder than IS-IS:
  - the OSPF LSAs are specified to carry fixed length addresses (either
    IPv4 or IPv6), so one would probably need to define a new (set of)
    LSAs for TRILL Not a big deal really, but IS-IS was designed to
    handle variable length NLRI from the start.
  - OSPF is designed to run on top of IP whereas IS-IS runs directly on
    IEEE 802.1. While rbridges (just like bridges) will probably be
    assigned IP addresses for management purposes (SNMP), requiring an IP
    address for the rbridge before it can start OSPF do build the
    topology would be a severe limitation. One would want to allow
    rbridges that don't have IP addresses (e.g. for home), or where the
    IP addresses are assigned after the rbridges have established
    connectivity across the link (assigned using stateless IPv6 or DHCP
    for instance).
    [Bob later told me: A possible choice when using OSPF is to use
    OSPFv3 over IPv6 and IPv6 link-local addresses, since any device with
    an IEEE MAC address can form an IPv6 link-local address.]

So trust me, I did really like to use OSPF here, because of the IS-IS
specification issues but also because there are more open source OSPF
code out there for implementors to reuse.

> While on the general topic, RIPv2 might even be a reasonable choice for 
> routing technology.  It's a lot simpler to implement and would still 
> work a lot better than spanning tree.

TRILL does add one additional constraint on a routing protocol (beyond
carrying MAC addresses around) which is to be able to construct a
spanning tree between the rbridges. The spanning tree is needed for
flooding (ARP, ND, and any other broadcast/multicast). Doing this in a
link state protocol is relatively easy; each router can independently
calculate the spanning tree in a consistent manner. But it is far from
clear whether this can be be done in a distance vector protocol.

Also, part of the goal for TRILL is to be better than the IEEE 802.1D
spanning tree, which has a worst-case convergence time of 45 seconds or
so. It isn't clear that RIP is a good fit for fast convergence.

> My general question is:  Is the decision on the routing technology to be 
> used for this going to be something that the w.g. decides or is it just 
> assumed it is ISIS?  I would favor the former approach, but in either 
> case I think it is important that the charter clarify this.

The TRILL WG would need to make the choice.
If the actual routing protocol work is farmed out to the specific,
long-lived routing protocol WGs, the success would depend on those WGs
having interest in this space.
An option is that the TRILL WG define the
extension to the routing protocols, and just have that reviewed by the
routing protocol WG(s).

    Erik

---

From: fltemplin at acm.org (Fred L. Templin)
Date: Sat Feb 5 07:31:32 2005

Erik,

There are a lot of peopole who know a lot more about routing
protocols than I do and I suspect even more than you and Bob.
Folks like Fred Baker, Charles Perkins and perhaps Dave Oran
just to name a few. Have they been following these discussions?

Fred
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Erik Nordmark
Sent: Friday, February 04, 2005 11:58 AM
To: [email-masked]
Subject: [rbridge] Choice of routing protocols

Below is an excerpt from emails between myself and Bob Hinden that tries
to capture some issues around the choice of routing protocol. Hopefully
this can stimulate further discussion on this topic.

    Erik

-------- Original Message --------
Subject: Re: Late agenda item?:  ipvlx charter
Date: Mon, 31 Jan 2005 10:24:35 -0800
From: Erik Nordmark <[email-masked]>
To: Bob Hinden <[email-masked]>

    assigned IP addresses for management purposes (SNMP), requiring an
IP
    OSPFv3 over IPv6 and IPv6 link-local addresses, since any device
with

having interest in this space. An option is that the TRILL WG define the

    Erik
_______________________________________________
rbridge mailing list
[email-masked] http://www.postel.org/mailman/listinfo/rbridge

---

From: fltemplin at acm.org (Fred L. Templin)
Date: Sun Feb 6 14:49:33 2005

I would like to apologize to Erik and to the list for my inappropriate
message. I was just trying to be helpful, but in hindsight I am sure
Erik would consult the appropriate routing experts as necessary and
that my more helpful alternative would have been to remain silent.

Sincerely,

Fred L. Templin
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Fred L. Templin
Sent: Saturday, February 05, 2005 7:30 AM
To: 'Developing a hybrid router/bridge.'
Subject: RE: [rbridge] Choice of routing protocols

Erik,

There are a lot of peopole who know a lot more about routing protocols
than I do and I suspect even more than you and Bob. Folks like Fred
Baker, Charles Perkins and perhaps Dave Oran just to name a few. Have
they been following these discussions?

Fred
[email-masked]

-----Original Message-----

    Erik

-------- Original Message --------
Subject: Re: Late agenda item?:  ipvlx charter
Date: Mon, 31 Jan 2005 10:24:35 -0800
From: Erik Nordmark <[email-masked]>
To: Bob Hinden <[email-masked]>

    Erik

---

From: hilarie at purplestreak.com (Hilarie Orman)
Date: Mon Feb 7 13:46:47 2005

Fred L. Templin declared on Sun, 6 Feb 2005 at 14:48:00 -0800 :

>  I am sure
>  Erik would consult the appropriate routing experts as necessary

I'd be sure, too, given Radia Perlman's involvement.  Isn't her
Infocomm paper the basis for the WG concept?  I think rbridge has no
lack of expertise.

Hilarie Orman

---

From: fltemplin at acm.org (Fred L. Templin)
Date: Mon Feb 7 15:55:45 2005

Thank you, Hilarie,

Again, no disrespect toward anyone was intended - especially
not toward Radia, Erik and Bob, the people whom I named on
the ill-concieved message and the many people on the rbridge
list who know much more about routing protocols than I do.

Sincerely,

Fred L. Templin
[email-masked]
[email-masked]

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Hilarie Orman
Sent: Monday, February 07, 2005 1:44 PM
To: [email-masked]
Subject: RE: [rbridge] Choice of routing protocols

>  Erik would consult the appropriate routing experts as necessary

I'd be sure, too, given Radia Perlman's involvement.  Isn't her Infocomm
paper the basis for the WG concept?  I think rbridge has no lack of
expertise.

Hilarie Orman

---

From: pekkas at netcore.fi (Pekka Savola)
Date: Mon Feb 7 23:46:10 2005

> Hopefully this can stimulate further discussion on this topic.

I'd also like to consider using OSPF as a basis for the simple reason 
that it has been widely implemented by the same vendors we'd like to 
ship Rbridges.  Those low-end router manufacturers don't implement 
IS-IS, so this would incur a steeper curve for implementation.

However, as for IPv6 one would have to use OSPFv3 as a basis (and then 
one could use draft-ietf-ospf-af-alt-01.txt), not OSPFv2, this does 
not seem to be all that relevant consideration anymore because those 
low-end vendors don't implement OSPFv3 in any case.

That said, the arguments below seem to indicate that using OSPF has 
some serious issues (mainly relating to IP address assignment) and 
IS-IS may be a better fit, with an automated NSAP address 
"generation".

To avoid rehashing this discussion over and over again, these 
considerations should be nailed down in the charter or an 
internet-draft.

>> I also wonder if we want to consider OSPF for this.  The IETF owns all the 
>> IPR and can produce derivative standards, where the situation with ISIS is 
>> very different (e.g., OSI owns the basic protocol). It's going to be 
>> difficult for an L2 bridge implementor to figure out and understand which 
>> collection of IETF and OSI specs to use.  Also, if I remember correctly, 
>> ISIS still requires manual configuration of 20 byte OSI NSAP addresses. 
>> This would be a pretty odd thing for a L2 bridge.
>
>> routing technology.  It's a lot simpler to implement and would still work a 
>> lot better than spanning tree.
>
>> assumed it is ISIS?  I would favor the former approach, but in either case 
>> I think it is important that the charter clarify this.
>
> [email-masked]
> http://www.postel.org/mailman/listinfo/rbridge
>

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: erik.nordmark at sun.com (Erik Nordmark)
Date: Wed Feb 9 13:52:55 2005

Pekka Savola wrote:

> one could use draft-ietf-ospf-af-alt-01.txt), not OSPFv2, this does not 
> seem to be all that relevant consideration anymore because those low-end 
> vendors don't implement OSPFv3 in any case.
> 
> That said, the arguments below seem to indicate that using OSPF has some 
> serious issues (mainly relating to IP address assignment) and IS-IS may 
> be a better fit, with an automated NSAP address "generation".
> 
> considerations should be nailed down in the charter or an internet-draft.

Excellent suggestion. Any volunteers for starting to capture this as an I-D?

    Erik