IS-IS as an IGP for a SP

Discussion in 'Cisco' started by J, Jul 28, 2006.

  1. J

    J Guest

    I'd like to seek out everyone's opinion on the use of IS-IS in a
    service provider network.

    Cisco highly recommends the use of IS-IS in SP networks. Their OSPF
    book tells SP users to consider IS-IS. Their ISP Essentials books
    basically says that EIGRP is used most often by beginners since it is
    so easy to set up. It goes on to say that OSPF is better because it
    forces good IGP design which helps scaling. Finally it says that IS-IS
    is used experienced users because it allows for even better scaling and
    more configuration options than either of the other two. From my
    experience I would have to agree with that. I have less experience
    with IS-IS but I've been studying hard on it for about a month both in
    and out of my lab.

    The network in question currently runs OSPF in a poorly conceived
    layout. Area 0 spans 3 POPs, one joined with fiber and the other
    joined via radio links. They are separated by about 80 miles. Area 0
    has been pushed out to all devices including devices in the access
    layer. This means that a AS5300 in one POP has full routes to all the
    Lo0 IPs in all the other POPs, all the PtP subnet everywhere, etc.
    Random other areas are in use across the network as well. The IGP
    isn't enormous by any means but it is about 95% crap. The network will
    be undergoing serious core upgrades in the next few months at the 2
    main POPs and will eventually be able to be called a professional
    network.

    We have met with about half a dozen SEs to discuss our design and
    configuration and they all strongly recommended IS-IS for our network.
    The faster convergence time will be greatly relied upon by the VoIP
    traffic that cross our network not only for phone over cable and ADSL2+
    users but also for customers with standard land lines (our software
    switches rely on this network for the switch to switch communication
    between POPs).

    Few people have even mentioned EIGRP for an application such as this.
    Most people agree on OSPF and IS-IS as the contenders. I agree with
    Cisco and vote for IS-IS.

    Does anyone have any applicable knowledge or experience that they would
    like to share? One of my questions involves the use of areas with a
    single POP. Should a POP be a single area or should we break up the
    IGP even more and place each large access device or types of access
    devices in a dedicated area? I'm thinking about placing the CMTSs in
    an area, the ATM routers for DSL in an area, the dialin in an area, etc
    (or each large access device in its own area. Every access device will
    be dual-homed to large core routers. Should I think more at where
    summarization would/could occur or the individual number of routes a
    device might stick in an IGP? We always summarize routes on access
    servers and ATM routers for this reason. I've mapped out the physical
    network and know where the L1 routers are (access devices) and L1-L2
    devices are (all edge and core routers in our design). The design
    contains no L2-only routers.

    Any input would be appreciated. I'm confident I could start rebuilding
    the IGP with IS-IS today, but I would like to hear everyone's thoughts
    on IS-IS from an operational standpoint.

    Thanks
    J
    J, Jul 28, 2006
    #1
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  2. J

    John Agosta Guest

    "J" <> wrote in message
    news:...
    > I'd like to seek out everyone's opinion on the use of IS-IS in a
    > service provider network.
    >
    > Cisco highly recommends the use of IS-IS in SP networks. Their OSPF
    > book tells SP users to consider IS-IS. Their ISP Essentials books
    > basically says that EIGRP is used most often by beginners since it is
    > so easy to set up. It goes on to say that OSPF is better because it
    > forces good IGP design which helps scaling. Finally it says that IS-IS
    > is used experienced users because it allows for even better scaling and
    > more configuration options than either of the other two. From my
    > experience I would have to agree with that. I have less experience
    > with IS-IS but I've been studying hard on it for about a month both in
    > and out of my lab.
    >
    > The network in question currently runs OSPF in a poorly conceived
    > layout. Area 0 spans 3 POPs, one joined with fiber and the other
    > joined via radio links. They are separated by about 80 miles. Area 0
    > has been pushed out to all devices including devices in the access
    > layer. This means that a AS5300 in one POP has full routes to all the
    > Lo0 IPs in all the other POPs, all the PtP subnet everywhere, etc.
    > Random other areas are in use across the network as well. The IGP
    > isn't enormous by any means but it is about 95% crap. The network will
    > be undergoing serious core upgrades in the next few months at the 2
    > main POPs and will eventually be able to be called a professional
    > network.
    >
    > We have met with about half a dozen SEs to discuss our design and
    > configuration and they all strongly recommended IS-IS for our network.
    > The faster convergence time will be greatly relied upon by the VoIP
    > traffic that cross our network not only for phone over cable and ADSL2+
    > users but also for customers with standard land lines (our software
    > switches rely on this network for the switch to switch communication
    > between POPs).
    >
    > Few people have even mentioned EIGRP for an application such as this.
    > Most people agree on OSPF and IS-IS as the contenders. I agree with
    > Cisco and vote for IS-IS.
    >
    > Does anyone have any applicable knowledge or experience that they would
    > like to share? One of my questions involves the use of areas with a
    > single POP. Should a POP be a single area or should we break up the
    > IGP even more and place each large access device or types of access
    > devices in a dedicated area? I'm thinking about placing the CMTSs in
    > an area, the ATM routers for DSL in an area, the dialin in an area, etc
    > (or each large access device in its own area. Every access device will
    > be dual-homed to large core routers. Should I think more at where
    > summarization would/could occur or the individual number of routes a
    > device might stick in an IGP? We always summarize routes on access
    > servers and ATM routers for this reason. I've mapped out the physical
    > network and know where the L1 routers are (access devices) and L1-L2
    > devices are (all edge and core routers in our design). The design
    > contains no L2-only routers.
    >
    > Any input would be appreciated. I'm confident I could start rebuilding
    > the IGP with IS-IS today, but I would like to hear everyone's thoughts
    > on IS-IS from an operational standpoint.
    >
    > Thanks
    > J



    I think IS-IS is a good choice because it allows for growth in a way where
    one doesn't have to worry
    as much about the 'grand plan' that OSPF brings to the table. It's a 'freer"
    protocol.
    Just remember to make sure you turn off the padding on "hello" messages
    between neighbors.
    1500 byte "hello" packets every few seconds can really start to hammer
    you....

    Have fun.
    John Agosta, Jul 29, 2006
    #2
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  3. J

    Merv Guest

    OSPF or ISIS, given a well though out design and a good implementation
    will function as an IGP for a service provider. ISIS is used by a
    number of tier 1 ISP's.

    Both OSPF and ISIS can be tuned to achieve sub-second convergence.

    If you segment the POP infrastrucutre into multiple areas ( and they
    are good reason to do so) watch out for cases of sub-optimal routing
    where to go from one POP area to another you must router back thru
    core. Check out the ISIS route leBoth aking feature.

    You might want to ask the Cisco SE why they recommend ISIS...

    Do your homework as switching IGP's is not a trivial task.



    some reading material:

    http://geocities.com/mnvbhatia/draft-bhatia-manral-diff-isis-ospf-00.txt

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

    http://www.vijaygill.com/oi.pdf


    IS-IS Deployment & Design Guidelines
    http://www.nanog.org/mtg-0202/ppt/isis/sld001.htm
    Merv, Jul 29, 2006
    #3
  4. J

    J Guest

    Merv wrote:
    > OSPF or ISIS, given a well though out design and a good implementation
    > will function as an IGP for a service provider. ISIS is used by a
    > number of tier 1 ISP's.
    >
    > Both OSPF and ISIS can be tuned to achieve sub-second convergence.
    >
    > If you segment the POP infrastrucutre into multiple areas ( and they
    > are good reason to do so) watch out for cases of sub-optimal routing
    > where to go from one POP area to another you must router back thru
    > core. Check out the ISIS route leBoth aking feature.
    >
    > You might want to ask the Cisco SE why they recommend ISIS...
    >
    > Do your homework as switching IGP's is not a trivial task.
    >
    >
    >
    > some reading material:
    >
    > http://geocities.com/mnvbhatia/draft-bhatia-manral-diff-isis-ospf-00.txt
    >
    > http://www.nanog.org/mtg-0006/katz.html
    >
    > http://www.vijaygill.com/oi.pdf
    >
    >
    > IS-IS Deployment & Design Guidelines
    > http://www.nanog.org/mtg-0202/ppt/isis/sld001.htm


    Thanks to both of you for the replies. There's lots of useful info
    there. I believe the underlying structure of IS-IS would be inherently
    very good for this network. Our network design just isn't condusive to
    OSPF's demanding "grand plan". I could make OSPF work and look decent
    in a single POP by going area crazy and using lots and lots of areas.
    Howver that's where the L1-L2 layering of IS-IS is a huge plus.

    Switching IGPs is a difficult task. Fortunately it won't be much more
    difficult than repairing the mess that's in place now. In fact I think
    it would actually be easier to implement IS-IS as I'm installing the
    new core than it would be to clean up OSPF because I won't have to
    redesign our OSPF areas or figure out how best to join 3 POPs without
    area 0 spanning them all.

    Between EIGRP, OSPF and IS-IS that arguement really comes down to OSPF
    and IS-IS. EIGRP just doesn't have the featureset that we need in an
    IGP. Between the other two we could make either of them work. However
    OSPF's reliance on a strict way of designing a network just isn't
    realistic in this scenario. IS-IS appears to be the best IGP for this
    network.

    One thing I forgot to mention is that eventually we will be bringing
    MPLS into our network. We will also be relying on significant amounts
    of mcast traffic later on in our design. I understand that IS-IS is
    MPLS capable. Are there any other gotchas that we should be aware of
    with respect to either technology?

    Thanks again for the reply. The info has been most helpful.
    J
    J, Jul 30, 2006
    #4
  5. J

    Steinar Haug Guest

    > One thing I forgot to mention is that eventually we will be bringing
    > MPLS into our network. We will also be relying on significant amounts
    > of mcast traffic later on in our design. I understand that IS-IS is
    > MPLS capable. Are there any other gotchas that we should be aware of
    > with respect to either technology?


    Both IS-IS and OSPF can carry TE info, which is what you are probably
    looking for.

    Steinar Haug, Nethelp consulting,
    Steinar Haug, Jul 30, 2006
    #5
  6. J

    J Guest

    Steinar Haug wrote:
    > > One thing I forgot to mention is that eventually we will be bringing
    > > MPLS into our network. We will also be relying on significant amounts
    > > of mcast traffic later on in our design. I understand that IS-IS is
    > > MPLS capable. Are there any other gotchas that we should be aware of
    > > with respect to either technology?

    >
    > Both IS-IS and OSPF can carry TE info, which is what you are probably
    > looking for.


    Thanks for the pointer. Would this also exclude EIGRP then?

    Thanks
    J
    J, Jul 30, 2006
    #6
  7. J

    Steinar Haug Guest

    > > Both IS-IS and OSPF can carry TE info, which is what you are probably
    > > looking for.

    >
    > Thanks for the pointer. Would this also exclude EIGRP then?


    Probably. I work for a service provider, and we have never seriously
    looked at EIGRP.

    Steinar Haug, Nethelp consulting,
    Steinar Haug, Jul 30, 2006
    #7
  8. J

    stephen Guest

    "Steinar Haug" <> wrote in message
    news:...
    > > > Both IS-IS and OSPF can carry TE info, which is what you are probably
    > > > looking for.

    > >
    > > Thanks for the pointer. Would this also exclude EIGRP then?

    >
    > Probably. I work for a service provider, and we have never seriously
    > looked at EIGRP.


    even if you ignore the suggestions so far, there is a different reason to
    leave out EIGRP.

    do you really want to make sure you cannot use a different brand of router
    or switch?

    If so, EIGRP is a good way to enforce that....
    >
    > Steinar Haug, Nethelp consulting,

    --
    Regards

    - replace xyz with ntl
    stephen, Jul 30, 2006
    #8
  9. J

    J Guest

    Steinar Haug wrote:
    > > > Both IS-IS and OSPF can carry TE info, which is what you are probably
    > > > looking for.

    > >
    > > Thanks for the pointer. Would this also exclude EIGRP then?

    >
    > Probably. I work for a service provider, and we have never seriously
    > looked at EIGRP.
    >
    > Steinar Haug, Nethelp consulting,


    I didn't consider EIGRP long after I researched IS-IS. EIGRP just
    isn't right for this network. Best I can tell I'd have to combine
    EIGRP and iBGP to get the granularity I need.

    J
    J, Jul 31, 2006
    #9
  10. J

    J Guest

    stephen wrote:
    > "Steinar Haug" <> wrote in message
    > news:...
    > > > > Both IS-IS and OSPF can carry TE info, which is what you are probably
    > > > > looking for.
    > > >
    > > > Thanks for the pointer. Would this also exclude EIGRP then?

    > >
    > > Probably. I work for a service provider, and we have never seriously
    > > looked at EIGRP.

    >
    > even if you ignore the suggestions so far, there is a different reason to
    > leave out EIGRP.
    >
    > do you really want to make sure you cannot use a different brand of router
    > or switch?
    >
    > If so, EIGRP is a good way to enforce that....


    That's a really good point. None of the 3 brands of CMTS on our
    network support EIGRP. The ADSL2+ solution we're looking at likely
    won't support EIGRP either. IS-IS may not be supported on either
    system but I'm sure OSPF will be. This of course wouldn't sway my
    decision not to use EIGRP. Since OSPF does not fit our network design
    this realization doesn't sway my decision in favor of OSPF either.
    Unless I can find another compelling reason to sway me towards OSPF
    then our IGP will definitely be IS-IS. Originally I'd considered iBGP
    with OSPF underpinnings for the loopbacks and PtPs. IS-IS is still the
    better solution.

    Thanks for the input
    J
    J, Jul 31, 2006
    #10
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