[afnog] afnog Digest, Vol 54, Issue 25
Global One Solution
malabow at gmail.com
Wed Sep 24 14:08:20 UTC 2008
IS-IS is becoming the protocol for ISP's, there are alot of improvement and
added features, Currently there is ONLY one Tier I ISP in the US that still
uses OSPF (uucchhh)... IS-IS rocks :)
Thanks,
On Wed, Sep 24, 2008 at 8:00 AM, <afnog-request at afnog.org> wrote:
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> Today's Topics:
>
> 1. Re: afnog Digest, Vol 54, Issue 23 (Peter Nyamukusa)
> 2. Re: afnog Digest, Vol 54, Issue 23 (Randy Bush)
> 3. Re: afnog Digest, Vol 54, Issue 23 (Peter Nyamukusa)
> 4. ospf and is-is (Randy Bush)
> 5. Re: afnog Digest, Vol 54, Issue 23 (Mark Tinka)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 24 Sep 2008 13:07:04 +0300
> From: "Peter Nyamukusa" <peter.nyamukusa at africaonline.co.tz>
> Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23
> To: <mtinka at globaltransit.net>, "'Frank A. Kuse'"
> <franko at africaonline.com.gh>
> Cc: afnog at afnog.org
> Message-ID:
> <057401c91e2d$4b94bbd0$e2be3370$@nyamukusa at africaonline.co.tz>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Mark,
>
> I migrated to ISIS from OSPF before deploying MPLS after taking some of the
> considerations below:
>
> * IS-IS does not use level 3 routers.
> * Some routers, called L1/L2 routers, belong to both area types.
> * Unlike OSPF, IS-IS routers are not required to be connected to a
> contiguous backbone area. In fact, the backbone area can also be segmented
> in IS-IS.
> * IS-IS uses the concepts of router levels, which is similar to OSPF
> areas. L2 routers are similar to OSPF backbone routers, and L1/L2 routers
> are analogous to OSPF ABRs.
> * With IS-IS, there is no restriction that all backbone routers (level 2
> routers) be contiguous
> such as the backbone area of OSPF.
> * In OSPF all areas must be directly linked to area 0, and the backbone
> area must also not be segmented.
> * With IS-IS, the backbone area can be more easily extended since all L2
> routers need not be linked directly together.
> * With regard to CPU use and the processing of routing updates, IS-IS is
> more efficient
> than OSPF.
> * In IS-IS, one LSP is sent per IS-IS router in each area (including
> redistributed prefixes [routes]), compared to the many OSPF LSAs that would
> be sent.
> * Not only are there fewer LSPs to process, but the mechanism by which
> IS-IS installs and withdraws prefixes is less processor intensive.
> * In IS-IS, the entire SPF table is not refreshed periodically like
> OSPF, which does so every 30 minutes by default.
>
> Try to design your network so it can run in a single area/level which
> makes things like TE/FRR or fast convergence easier later..
> but again the choice is up to you
>
> Cheers
> Peter
>
> -----Original Message-----
> From: afnog-bounces at afnog.org [mailto:afnog-bounces at afnog.org] On Behalf
> Of
> Mark Tinka
> Sent: Wednesday, September 24, 2008 12:34 PM
> To: Frank A. Kuse
> Cc: afnog at afnog.org
> Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23
>
> On Wednesday 24 September 2008 17:18:29 Frank A. Kuse wrote:
>
> > For now we have reverted all interfaces to be similar but we know that
> > based on what Mark and Peter sent, if we change MTU on the gigabit
> > interface to 1500, mpls works fine.
>
> Just curious, were you running IS-IS as your network's IGP before you
> decided to setup MPLS, or did you setup IS-IS with the sole purpose of
> running MPLS?
>
> Cheers,
>
> Mark.
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 24 Sep 2008 19:30:00 +0900
> From: Randy Bush <randy at psg.com>
> Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23
> To: Peter Nyamukusa <peter.nyamukusa at africaonline.co.tz>
> Cc: "'Frank A. Kuse'" <franko at africaonline.com.gh>, afnog at afnog.org
> Message-ID: <48DA16A8.4090705 at psg.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> the way we old folk say it is
>
> is-is is used by very few isps. just the old stable ones.
>
> :)
>
> randy
>
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 24 Sep 2008 14:10:05 +0300
> From: "Peter Nyamukusa" <peter.nyamukusa at africaonline.co.tz>
> Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23
> To: "'Randy Bush'" <randy at psg.com>
> Cc: "'Frank A. Kuse'" <franko at africaonline.com.gh>, afnog at afnog.org
> Message-ID:
> <059101c91e36$197fc140$4c7f43c0$@nyamukusa at africaonline.co.tz>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Randy,
>
> I see this topic has taken a slight twist but never the less below are some
> comparison between ISIS and OSPF this is from Wikipedia so I don't know if
> it is really true when they say ISIS is favoured in ISP environments
> because
> it can support more routers in an area. I sure that would be true if you
> have may routers in your backbone area right now I have over 20 and that
> number should increase to over 100 within the next few months.
>
> NB. I not trying to influence your choice OSPF is great I been using it for
> many years
>
> ISIS Vs OSPF
>
> Both IS-IS and OSPF are link state protocols, and both use the same
> Dijkstra
> algorithm for computing the best path through the network. As a result,
> they
> are conceptually similar. Both support variable length subnet masks, can
> use
> multicast to discover neighboring routers using hello packets, and can
> support authentication of routing updates.
>
> While OSPF is natively built to route IP and is itself a Layer 3 protocol
> that runs on top of IP, IS-IS is natively an ISO network layer protocol (it
> is at the same layer as CLNS), a fact that may have allowed OSPF to be more
> widely used. IS-IS does not use IP to carry routing information messages.
>
> IS-IS routers build a topological representation of the network. This map
> indicates the IP subnets which each IS-IS router can reach, and the lowest
> cost (shortest) path to an IP subnet is used to forward IP traffic.
>
> IS-IS also differs from OSPF in the methods by which it reliably floods
> topology and topology change information through the network. However, the
> basic concepts are similar.
>
> Since OSPF is more popular, this protocol has a richer set of extensions
> and
> added features. However IS-IS is less "chatty" and can scale to support
> larger networks. Given the same set of resources, IS-IS can support more
> routers in an area than OSPF. This makes IS-IS favoured in ISP
> environments.
> Additionally, IS-IS is neutral regarding the type of network addresses for
> which it can route. OSPF, on the other hand, was designed for IPv4. Thus
> IS-IS was easily adapted to support IPv6, while the OSPF protocol needed a
> major overhaul (OSPF v3).
>
> The TCP/IP implementation, known as "Integrated IS-IS" or "Dual IS-IS", is
> described in RFC 1195.
>
> IS-IS differs from OSPF in the way that "areas" are defined and routed
> between. IS-IS routers are designated as being: Level 1 (intra-area); Level
> 2 (inter area); or Level 1-2 (both). Level 2 routers are inter area routers
> that can only form relationships with other Level 2 routers. Routing
> information is exchanged between Level 1 routers and other Level 1 routers,
> and Level 2 routers only exchange information with other Level 2 routers.
> Level 1-2 routers exchange information with both levels and are used to
> connect the inter area routers with the intra area routers. In OSPF, areas
> are delineated on the interface such that an area border router (ABR) is
> actually in two or more areas at once, effectively creating the borders
> between areas inside the ABR, whereas in IS-IS area borders are in between
> routers, designated as Level 2 or Level 1-2. The result is that an IS-IS
> router is only ever a part of a single area. IS-IS also does not require
> Area 0 (Area Zero) to be the backbone area through which all inter-area
> traffic must pass. The logical view is that OSPF creates something of a
> spider web or star topology of many areas all attached directly to Area
> Zero
> and IS-IS by contrast creates a logical topology of a backbone of Level 2
> routers with branches of Level 1-2 and Level 1 routers forming the
> individual areas.
>
> Cheers
>
> Peter
>
> -----Original Message-----
> From: Randy Bush [mailto:randy at psg.com]
> Sent: Wednesday, September 24, 2008 1:30 PM
> To: Peter Nyamukusa
> Cc: mtinka at globaltransit.net; 'Frank A. Kuse'; afnog at afnog.org
> Subject: [!! SPAM] Re: [afnog] afnog Digest, Vol 54, Issue 23
>
> the way we old folk say it is
>
> is-is is used by very few isps. just the old stable ones.
>
> :)
>
> randy
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Wed, 24 Sep 2008 20:40:17 +0900
> From: Randy Bush <randy at psg.com>
> Subject: [afnog] ospf and is-is
> To: Peter Nyamukusa <peter.nyamukusa at africaonline.co.tz>
> Cc: AFNOG <afnog at afnog.org>
> Message-ID: <48DA2721.70704 at psg.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> >> is-is is used by very few isps. just the old stable ones.
> > I not trying to influence your choice OSPF is great I been using it for
> > many years
>
> you seem to have misread my message. when you get to be my age, old and
> stable are good things.
>
> this old dog's view is more like
>
> o when we built the earlier networks, is-is worked simply and well,
> dave katz was (and still is!) a rigorous and very clean implementor.
>
> o ospf was new and buggy. so simply not a choice. it was not usable
> until into the '90s.
>
> o as the internet grew, the ietf embellished ospf in the way that the
> ietf does things. more complexity, flakier, ...
>
> o is-is is not editable by the ietf. so it stayed simpler and more
> stable.
>
> o then there are features, e.g. hard to attack is-is at the ip layer.
> your previous message was good detail of today's state of play.
>
> o and then the old dogs went to new startups and spread our lazy way
> of doing things.
>
> i hope all my competitors use ospf. :)
>
> randy
>
>
>
> ------------------------------
>
> Message: 5
> Date: Wed, 24 Sep 2008 19:46:49 +0800
> From: Mark Tinka <mtinka at globaltransit.net>
> Subject: Re: [afnog] afnog Digest, Vol 54, Issue 23
> To: "Peter Nyamukusa" <peter.nyamukusa at africaonline.co.tz>
> Cc: "'Frank A. Kuse'" <franko at africaonline.com.gh>, afnog at afnog.org
> Message-ID: <200809241946.55809.mtinka at globaltransit.net>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On Wednesday 24 September 2008 18:07:04 Peter Nyamukusa
> wrote:
>
> > * IS-IS does not use level 3 routers.
>
> Well, L3 routing is inter-domain. OSI's approach was IDRP.
>
> > * Unlike OSPF, IS-IS routers are not required
> > to be connected to a contiguous backbone area. In fact,
> > the backbone area can also be segmented in IS-IS.
>
> A major advantage when expanding your network beyond
> multiple regions.
>
> > * With IS-IS, there is no restriction that all
> > backbone routers (level 2 routers) be contiguous
> > such as the backbone area of OSPF.
>
> Actually, there is...
>
> If you deploy a hierarchical IS-IS network (L1 routers
> within the PoP's, L2 [or rather, L1/L2] routers in the
> core), your L2 backbone MUST be contiguous.
>
> The merit is that L1 routers don't need to be contiguous
> between PoP's. Route leaking ensures optimal routing
> (longest match) between PoP's.
>
> > * In OSPF all areas must be directly linked to area
> > 0, and the backbone area must also not be segmented.
>
> A problem for networks that build "wide".
>
> > * With IS-IS, the backbone area can be more easily
> > extended since all L2 routers need not be linked directly
> > together.
>
> Actually, it's the other way around; L1 routers do not need
> to be linked directly.
>
> However, L2 or L1/L2 routers should be contiguously
> deployed. L2 or L1/L2 "snake" their course in between L1
> routers across the various regions an ISP may deploy its
> network.
>
> > * With regard to CPU use and the processing of
> > routing updates, IS-IS is more efficient
> > than OSPF.
>
> IS-IS is fundamentally less chatty than OSPF on the wire.
> Both IGP's have several knobs and switches that can be
> manipulated to make the deployment even more scalable,
> e.g., the LSP lifetime can be configured up to 18.2hrs in
> IS-IS, which makes it quite suitable for large deployments,
> e.t.c.
>
> It's also good to note that IS-IS was easily extendable for
> the inclusion of new features, e.g., IPv6 routing, as it
> utilizes TLV's, rather than OSPFv2 which uses the "Options"
> field (already depleted) - hence the transition to a new
> OSPF protocol, OSPFv3.
>
> Suffice it to say that 'draft-ietf-ospf-af-alt-07.txt'
> (expired the last time I checked) attempts to extend OSPFv3
> by adding multiple address families, one of which is IPv4
> (Unicast and Multicast). Of course, it runs over IPv6, so
> an IPv6 network would be a requirement for running IPv4
> over OSPFv3. Vendor support has already emerged from
> Juniper... but I digress.
>
> And then of course, IS-IS runs directly over the data link
> layer.
>
> > Try to design your network so it can run in a single
> > area/level which makes things like TE/FRR...
>
> I believe a hierarchical network design provides better
> scalability.
>
> Besides, I'd design my IS-IS backbone with IP in mind. Other
> features like MPLS-TE and FRR are secondary (as they depend
> on a stable IP foundation).
>
> However, it is true that inter-area CSPF for MPLS-TE does
> not exist today (major vendors have planned to support it,
> though). LSR's have to be 'loosely' defined in the path
> list for RSVP to successfully signal an inter-area LSP.
>
> We, generally, treat MPLS-TE as a tactical response to a
> potential congestion problem, rather than a lasting
> solution, especially since very few points would be
> affected in the grand scheme of things... so manual
> inter-area MPLS-TE isn't an issue.
>
> Cheers,
>
> Mark.
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--
Liban Mohamed
Global One Solution
www.globalonesolutions.net
malabow at gmail.com
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