IX , route reflector??

Discussion in 'Cisco' started by pvsnmp@yahoo.com, Jan 29, 2005.

  1. Guest

    Hi,
    I was wondering abt this IX architecture
    http://www.nixi.org/technical/n_design.htm
    Is the IX router acting as route reflector??If yes, can a route
    reflector client be an EBGP peer?
    If no , how does this become L2 IXP?
    Another question
    Assume the above topology, and the peering is as given in the
    diagram.The IX router is not a route reflector.All the routers
    connected to the switch are in the same subnet.When the IX router
    advertises the routes of ISPA to ISPB what will be the NextHop
    Attribute value?Will it be the IX router's ip address or the ISPA
    router's IP address , as all are in same subnet ??
    thanks and regards,
    Prashant
     
    , Jan 29, 2005
    #1
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  2. In article <>,
    wrote:

    > Hi,
    > I was wondering abt this IX architecture
    > http://www.nixi.org/technical/n_design.htm
    > Is the IX router acting as route reflector??If yes, can a route
    > reflector client be an EBGP peer?


    "route reflector" is an IBGP concept, since the normal behavior in IBGP
    is that you don't pass on routes learned from other IBGP peers (because
    the IBGP routers are supposed to be a full mesh). EBGP peers pass on
    all their BGP routes, whether they're learned via IBGP or EBGP. In a
    sense, you could say that EBGP peers are always route reflectors.

    > If no , how does this become L2 IXP?
    > Another question
    > Assume the above topology, and the peering is as given in the
    > diagram.The IX router is not a route reflector.All the routers
    > connected to the switch are in the same subnet.When the IX router
    > advertises the routes of ISPA to ISPB what will be the NextHop
    > Attribute value?Will it be the IX router's ip address or the ISPA
    > router's IP address , as all are in same subnet ??


    Since they're all on the same subnet, it can advertise the ISPA address.
    RFC 1771 says:

    A BGP speaker can advertise any external border router as the next hop,
    provided that the IP address of this border router was learned from one
    of the BGP speaker's peers, and the interface associated with the IP
    address of this border router (as specified in the NEXT_HOP path
    attribute) shares a common subnet with the local and remote BGP
    speakers.

    --
    Barry Margolin,
    Arlington, MA
    *** PLEASE post questions in newsgroups, not directly to me ***
     
    Barry Margolin, Jan 29, 2005
    #2
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  3. On 29.01.2005 10:50 wrote

    > Hi,
    > I was wondering abt this IX architecture
    > http://www.nixi.org/technical/n_design.htm
    > Is the IX router acting as route reflector??If yes, can a route
    > reflector client be an EBGP peer?
    > If no , how does this become L2 IXP?
    > Another question
    > Assume the above topology, and the peering is as given in the
    > diagram.The IX router is not a route reflector.All the routers
    > connected to the switch are in the same subnet.When the IX router
    > advertises the routes of ISPA to ISPB what will be the NextHop
    > Attribute value?Will it be the IX router's ip address or the ISPA
    > router's IP address , as all are in same subnet ??


    because of BGP's next hop feature at an IXP can act as a route-server.
    While not absolutely perfect a route-server will give you full
    connectivity by only setting up one BGP session. Look at big European
    IXP like AMS-IX, LINX or DE-CIX where you have 150 - 200 peers to see
    how a route-server does help. A route-server still runs BGP best path
    selection and only re-announces the best path. But there is researc to
    overcome this limitation (see
    http://www.rfc-editor.org/internet-drafts/draft-bhatia-ecmp-routes-in-bgp-01.txt)





    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Jan 29, 2005
    #3
  4. Prashant Guest

    Hi,
    thanks for the reply.Are these IXs using route-server which is normal
    cisco router or some unix based server?How different is a route-server
    when compared to a cisco router running eBGP? Why do most L2 IXPs use
    route-reflector or route-server when the same can be achieved by a
    cisco router running eBGP with ISPs(the ISP routers are connected to L2
    switch unlike L3 exchange where the ISP routers are connected to the IX
    router directly.)
    Please correct me if i am wrong.

    thanks and regards,
    Prashant
     
    Prashant, Jan 30, 2005
    #4
  5. On 30.01.2005 11:04 Prashant wrote

    > Are these IXs using route-server which is normal cisco router or some
    > unix based server?


    Mostly Unix servers as this is more flexible, powerful and cheaper

    > How different is a route-server when compared to a cisco router
    > running eBGP?


    nothing

    > Why do most L2 IXPs use route-reflector or route-server when the same
    > can be achieved by a cisco router running eBGP with ISPs(the ISP
    > routers are connected to L2 switch unlike L3 exchange where the ISP
    > routers are connected to the IX router directly.)


    because using *nix based route-servers (== quagga/zebra) is more
    flexible, powerful and cheaper (actually you are only using the bgpd
    daemon. No need for expensive forwarding devices. And the *nix boxes
    have faster CPU and more RAM. They also offer nice features like the
    transparent thingy, i.e transparent next hop, MED and ASN)





    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Jan 30, 2005
    #5
  6. Arien Vijn Guest

    Hi,

    Prashant wrote:

    > thanks for the reply.Are these IXs using route-server which is normal
    > cisco router or some unix based server?


    AMS-IX does not and did not have any route server. Peerings at AMS-IX
    are purely bilateral arrangements between members.

    Having said that, we will set two route servers soon. The number of
    sessions at AMS-IX is becoming too large to handle - both for
    operators and routers.

    These route servers will be based on general-purpose UNIX servers
    running a BGP daemon.

    > How different is a route-server when compared to a cisco router
    > running eBGP?


    Routers are expensive devices, mostly because mordern routers are
    optimized to forward high amounts of traffic. Many high-end routers
    are equipped with relatively small CPUs as forwarding is done in ASICs.
    Once everything is up and running the CPU does not have to do much. But
    the BGP process is typically CPU-bound. Some types of high-end routers
    clearly have difficulties to establish a few hundred sessions.

    Route servers only have to do BGP, they do not have to do forwarding.
    UNIX based servers are relatively cheap and are equipped with really
    fast CPUs. So it is likely that they will be better and less expensive
    route servers than routers.

    > Why do most L2 IXPs use route-reflector or route-server when the
    > same can be achieved by a cisco router running eBGP with ISPs(the ISP


    > routers are connected to L2 switch unlike L3 exchange where the ISP
    > routers are connected to the IX router directly.)
    > Please correct me if i am wrong.


    I am not sure if I understand you. But route servers are mostly an
    extra service. Strictly, they are not necessary on L2-exchanges.
    Connected ISPs can peer bilaterally over the shared infrastructure.
    As said, a successful IXP as AMS-IX does not have any, yet.
    Kind regards, Arien
     
    Arien Vijn, Jan 30, 2005
    #6
  7. Prashant Guest

    thanks very much for the explanation.
    A few more questions.
    If you go through the internet draft on ecmp routes which Arnold has
    referred to , its mentioned that the bgp router periodically chks if
    the next-hops are reachable and runs bgp decision algorithm .Is it
    true?

    I have read some documents where there is a comparison of the various
    IX topologies .I have read that route servers permit bilateral
    agreements but the use route-reflector permits only multilateral
    agreement.
    What does this actually mean ??

    thanks and regards,
    Prashant
     
    Prashant, Feb 4, 2005
    #7
  8. Arien Vijn Guest

    "Prashant" <> wrote in message news:<>...
    > thanks very much for the explanation.
    > A few more questions.
    > If you go through the internet draft on ecmp routes which Arnold has
    > referred to , its mentioned that the bgp router periodically chks if
    > the next-hops are reachable and runs bgp decision algorithm .Is it
    > true?


    Please elaborate your question.

    > I have read some documents where there is a comparison of the various
    > IX topologies .I have read that route servers permit bilateral
    > agreements but the use route-reflector permits only multilateral
    > agreement.
    > What does this actually mean ??


    Multilateral, in this context, usually means that one party agrees to
    accept traffic from all other parties using the same route server.
    Hence everyone is interconnecting with everyone else. It's all or
    nothing so to speak.

    Bilateral is applicable to two parties agreeing to interconnect with
    each other. This means that connected parties have the choice _not_ to
    interconnect with everyone else. This makes it possible to make
    case-by-case decisions.

    -- Arien
     
    Arien Vijn, Feb 5, 2005
    #8
  9. Prashant Guest

    Arien Vijn wrote:
    > "Prashant" <> wrote in message

    news:<>...
    > > thanks very much for the explanation.
    > > A few more questions.
    > > If you go through the internet draft on ecmp routes which Arnold

    has
    > > referred to , its mentioned that the bgp router periodically chks

    if
    > > the next-hops are reachable and runs bgp decision algorithm .Is it
    > > true?

    >
    > Please elaborate your question.
    >
    > > I have read some documents where there is a comparison of the

    various
    > > IX topologies .I have read that route servers permit bilateral
    > > agreements but the use route-reflector permits only multilateral
    > > agreement.
    > > What does this actually mean ??

    >
    > Multilateral, in this context, usually means that one party agrees to
    > accept traffic from all other parties using the same route server.
    > Hence everyone is interconnecting with everyone else. It's all or
    > nothing so to speak.
    >
    > Bilateral is applicable to two parties agreeing to interconnect with
    > each other. This means that connected parties have the choice _not_

    to
    > interconnect with everyone else. This makes it possible to make
    > case-by-case decisions.
    >
    > -- Arien


    Hi,

    About the first question:
    If you refer
    http://www.rfc-editor.org/internet-drafts/draft-bhatia-ecmp-routes-in-bgp-01.txt

    in section 2. under the subtitle "Avoiding Persistent Route
    Oscillations " , step [9] states "Ra at this time has only two routes.
    One, learnt from R1 and the other learnt from R2. It has selected the
    route learnt from R2. After
    some time, this router runs its scanner process for validating the
    NEXT_HOPs. There it runs the best path algorithm ......"

    I just wanted to know if its true that a BGP router runs BGP decision
    process periodically, because i havent read about such a thing before.

    thanks and regards,
    Prashant
     
    Prashant, Feb 6, 2005
    #9
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