IBGP Peering

Discussion in 'Cisco' started by Sandy Manning, Nov 26, 2004.

  1. I have 3-routers that are directly connected to each other. Here is
    an example drawing of the connectivity. One ethernet from RTRA to
    RTRB and one ethernet from RTRB to RTRC.

    RTRA----RTRB----RTRC

    RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP. RTRA
    connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC connects to
    AS3.

    How can I configure the IBGP to run properly in this topology?

    Sandy Manning
    BGP Neophite
     
    Sandy Manning, Nov 26, 2004
    #1
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  2. On 26.11.2004 21:43 Sandy Manning wrote


    > I have 3-routers that are directly connected to each other. Here is
    > an example drawing of the connectivity. One ethernet from RTRA to
    > RTRB and one ethernet from RTRB to RTRC.
    >
    > RTRA----RTRB----RTRC
    >
    > RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP. RTRA
    > connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC connects to
    > AS3.
    >
    > How can I configure the IBGP to run properly in this topology?
    >


    Given

    RTRA----RTRB network: 192.168.0.0/24, A .1, B .2
    RTRB----RTRC network: 192.168.1.0/24, B .2, C .1

    RTRA:
    =====
    router bgp 2
    neighbor 192.168.0.2 remote-as 2
    neighbor 192.168.1.1 remote-as 2

    RTRB:
    =====
    router bgp 2
    neighbor 192.168.0.1 remote-as 2
    neighbor 192.168.1.1 remote-as 2

    RTRC:
    =====
    router bgp 2
    neighbor 192.168.0.1 remote-as 2
    neighbor 192.168.1.2 remote-as 2


    Make sure by IGP that RTRA knows how to reach RTRC and that RTRC knows
    how to reach RTRA.




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 26, 2004
    #2
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  3. Sandy Manning

    Toby Guest

    Hi

    Not going to do all the work for you, but some things to consider

    RTRB shouldnt need to run BGP as it is only in One AS, BGP is used to pass
    routing updates between AS's
    IBGP is used to pass routing info between border routers within one AS for
    onward transport. i.e AS0 info needs passing to AS3 and is achieved by IBGP
    between RTRA and RTRC so a IBGP neibourship needs to be established between
    RTRA &C not B
    EBGP passes routing updates between AS's
    RTRA,B & C should have a Internal routing protocol running between them such
    as OSPF, ISIS. Use passive interface commands to stop leakage of this
    between AS's
    Packets being routed need to have a destination network in the routing table
    even when running through routers not running BGP so BGP is normally
    redistributed into the OSPF, ISIS but you have to be careful not to create
    routing loops so dont redistribute OSPF, ISIS into B
    Your BGP neighbours need to be reachable to create the peering to start with
    so you may have to include static routes to ensure this.
    If you are using loopback addresses to peer to you will need to include
    neighbor x.x.x.x update-source Loopback0
    And for EBGP neighbours you may need neighbor x.x.x.x ebgp-multihop 3 where
    3 is the number of hops from your loopback to the neighbours loopback.

    Regards

    Toby

    "Sandy Manning" <> wrote in message
    news:...
    >I have 3-routers that are directly connected to each other. Here is
    > an example drawing of the connectivity. One ethernet from RTRA to
    > RTRB and one ethernet from RTRB to RTRC.
    >
    > RTRA----RTRB----RTRC
    >
    > RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP. RTRA
    > connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC connects to
    > AS3.
    >
    > How can I configure the IBGP to run properly in this topology?
    >
    > Sandy Manning
    > BGP Neophite
     
    Toby, Nov 26, 2004
    #3
  4. On 26.11.2004 22:30 Toby wrote

    > RTRB shouldnt need to run BGP as it is only in One AS, BGP is used to pass
    > routing updates between AS's


    Not commenting on all you wrote: but how will RTRB know where to forward
    packets for prefix e.g. 212.250.0.0/16. Assume RTRB defaults to RTRC but
    212.250.0.0/16 has to be routed via RTRA.



    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 26, 2004
    #4
  5. Sandy Manning

    Toby Guest

    Hi

    I agree I have thought of this as a transit AS only and answered in a
    rush.just trying to give food for thought and it is wrong with the
    redistribution etc. I realise this myself after I posted it.

    Toby

    "Arnold Nipper" <> wrote in message
    news:co8as0$b25$...
    > On 26.11.2004 22:30 Toby wrote
    >
    >> RTRB shouldnt need to run BGP as it is only in One AS, BGP is used to
    >> pass routing updates between AS's

    >
    > Not commenting on all you wrote: but how will RTRB know where to forward
    > packets for prefix e.g. 212.250.0.0/16. Assume RTRB defaults to RTRC but
    > 212.250.0.0/16 has to be routed via RTRA.
    >
    >
    >
    > Arnold
    > --
    > Arnold Nipper, AN45
     
    Toby, Nov 26, 2004
    #5
  6. Sandy Manning

    Ivan Ostreš Guest

    In article <co866h$35c$>, says...
    > RTRB:
    > =====
    > router bgp 2
    > neighbor 192.168.0.1 remote-as 2
    > neighbor 192.168.1.1 remote-as 2
    >
    > Make sure by IGP that RTRA knows how to reach RTRC and that RTRC knows
    > how to reach RTRA.
    >
    >


    I would expect here that router B will NOT pass prefixes learned from
    peer A to peer C and vice versa since that is one of the IBGP rules.
    (You need to have a full mesh of internal BGP routers or route
    reflectors).

    So, I would configure RTRB as route-reflector:

    router bgp 2
    no sync
    neighbor 192.168.0.1 remote-as 2
    neighbor 192.168.0.1 route-reflector-client
    neighbor 192.168.1.1 remote-as 2
    neighbor 192.168.1.1 route-reflector-client

    Now it should work ok.

    HTH,

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Nov 28, 2004
    #6
  7. On 28.11.2004 14:48 Ivan Ostreš wrote


    > In article <co866h$35c$>, says...
    >> RTRB:
    >> =====
    >> router bgp 2
    >> neighbor 192.168.0.1 remote-as 2
    >> neighbor 192.168.1.1 remote-as 2
    >>
    >> Make sure by IGP that RTRA knows how to reach RTRC and that RTRC knows
    >> how to reach RTRA.
    >>
    >>

    >
    > I would expect here that router B will NOT pass prefixes learned from
    > peer A to peer C and vice versa since that is one of the IBGP rules.
    > (You need to have a full mesh of internal BGP routers or route
    > reflectors).
    >


    If you read carefully you see that RTRA, RTRB and RTRC *are* fully meshed.

    > So, I would configure RTRB as route-reflector:
    >


    You don't need it.

    > Now it should work ok.
    >


    It already will have done before ...




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 28, 2004
    #7
  8. Arnold, Ivan and, Toby,

    I did think of using RR (route-reflectors) but, I read that in order
    to setup RR's the router configured as the RR must be the hub and the
    others must act as the spokes? If this is true, the problem with my
    configuration is that I cannot change the physical connectivity
    meaning that RTRA must stay the EBGP peer to the remote-AS AS0.

    If the hub rule is true should I only run BGP on RTRA and RTRC and use
    OSPF to route between them? IF this is hub rule is false, how can I
    setup BGP under this rigid configuration to make IBGP work without a
    full mesh or RR's?

    RTRA----RTRB----RTRC

    Sandy Manning



    (Sandy Manning) wrote in message news:<>...
    > I have 3-routers that are directly connected to each other. Here is
    > an example drawing of the connectivity. One ethernet from RTRA to
    > RTRB and one ethernet from RTRB to RTRC.
    >
    > RTRA----RTRB----RTRC
    >
    > RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP. RTRA
    > connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC connects to
    > AS3.
    >
    > How can I configure the IBGP to run properly in this topology?
    >
    > Sandy Manning
    > BGP Neophite
     
    Sandy Manning, Nov 28, 2004
    #8
  9. Guys,

    I thought of using a RR (route-reflector) but from what I have read on
    RR's the rule is, the router configured as the RR must be the
    HUB-router in the configuration, act as the EBGP peer to the remote-as
    and, the other routers must connected as and act as spokes? My
    problem is for design reasons, I cannot change the physical
    configuration of the network. So, RTRA must stay the EGBP connection
    to the remote-as AS0.

    RTRA(Bdr for AS0-remote and AS1)-----RTRB(AS1)-----RTRC(Brdr for AS1
    and AS2)

    IF the HUB RULE FOR RR'S is true? Should I, on RTRA run EBGP to the
    remote-as AS0 and also run an OSPF process. RTRB and RTRC run an OSPF
    process. RTRC run BGP Process for redistribution of the remote-as AS2
    routes?

    or

    If the Hub rule is not true for RR's how can I configure a RR without
    the hub and spoke?

    Thanks in advance for your help.

    Sandy Manning
    BGP Neophite
     
    Sandy Manning, Nov 28, 2004
    #9
  10. On 28.11.2004 22:55 Sandy Manning wrote


    > Guys,
    >
    > I thought of using a RR (route-reflector) but from what I have read on
    > RR's the rule is, the router configured as the RR must be the
    > HUB-router in the configuration, act as the EBGP peer to the remote-as
    > and, the other routers must connected as and act as spokes?


    Check
    http://www.cisco.com/en/US/products..._guide_chapter09186a00800ca763.html#wp1001965
    for a comprehensive tutorial on route reflecting.

    btw: if RTRA, RTRB and RTRC is all you have, you don't need a route
    reflector.



    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 28, 2004
    #10
  11. Sandy Manning

    Ivan Ostreš Guest

    In article <>, says...
    > On 28.11.2004 14:48 Ivan Ostre=9A wrote
    >
    > If you read carefully you see that RTRA, RTRB and RTRC *are* fully meshed=
    > =2E
    >


    Hi Arnold,

    Following is the original post:


    >>> I have 3-routers that are directly connected to each other. Here is
    >>> an example drawing of the connectivity. One ethernet from RTRA to
    >>> RTRB and one ethernet from RTRB to RTRC.
    >>>
    >>> RTRA----RTRB----RTRC
    >>>
    >>> RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP.
    >>> RTRA connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC
    >>> connects to AS3.
    >>>
    >>> How can I configure the IBGP to run properly in this topology?



    Where do you see here that peers are fully meshed? (I just don't see
    that in OP, so please point that out for me, I would be gratefull).


    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Nov 29, 2004
    #11
  12. Sandy Manning

    Ivan Ostreš Guest

    In article <>,
    says...
    > Guys,
    >
    > I thought of using a RR (route-reflector) but from what I have read on
    > RR's the rule is, the router configured as the RR must be the
    > HUB-router in the configuration, act as the EBGP peer to the remote-as
    > and, the other routers must connected as and act as spokes? My
    > problem is for design reasons, I cannot change the physical
    > configuration of the network. So, RTRA must stay the EGBP connection
    > to the remote-as AS0.
    >
    > RTRA(Bdr for AS0-remote and AS1)-----RTRB(AS1)-----RTRC(Brdr for AS1
    > and AS2)
    >
    > IF the HUB RULE FOR RR'S is true? Should I, on RTRA run EBGP to the
    > remote-as AS0 and also run an OSPF process. RTRB and RTRC run an OSPF
    > process. RTRC run BGP Process for redistribution of the remote-as AS2
    > routes?
    >
    > or
    >
    > If the Hub rule is not true for RR's how can I configure a RR without
    > the hub and spoke?
    >


    If your peers ARE loggically fully meshed (that's what Arnold said) then
    you do NOT need Route reflectors.

    If your peers are NOT loggically fully meshed you need to make RTRB a
    RR.

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Nov 29, 2004
    #12
  13. On 29.11.2004 09:04 Ivan Ostreš wrote

    >>>> RTRA runs EBGP and IBGP. RTRB IBGP only, and RTRC EBGP and IBGP.
    >>>> RTRA connects to AS0. RTRA, RTRB, and RTRC are in AS2. RTRC
    >>>> connects to AS3.
    >>>>
    >>>> How can I configure the IBGP to run properly in this topology?

    >
    >
    > Where do you see here that peers are fully meshed? (I just don't see
    > that in OP, so please point that out for me, I would be gratefull).
    >


    Just read news://co866h$35c$ where I put down the config
    for all three routers. Each routers has two different neighbors. I.e. A
    peers with B and C, B peers with A and C and C peers with A and B. Hence
    all are fully meshed. q.e.d. :)




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 29, 2004
    #13
  14. On 29.11.2004 09:07 Ivan Ostreš wrote

    >
    > If your peers ARE loggically fully meshed (that's what Arnold said) then
    > you do NOT need Route reflectors.
    >
    > If your peers are NOT loggically fully meshed you need to make RTRB a
    > RR.
    >


    What do you mean by "logically fully meshed"? I've never heard this before.




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 29, 2004
    #14
  15. Sandy Manning

    Ivan Ostreš Guest

    In article <cof9c9$3hl$>, says...
    > Just read news://co866h$35c$ where I put down the config=20
    > for all three routers. Each routers has two different neighbors. I.e. A=20
    > peers with B and C, B peers with A and C and C peers with A and B. Hence =
    >
    > all are fully meshed. q.e.d. :)
    >
    >


    Hm... I agree that this was in YOUR post, not OP. Anyway, I agree that
    your full mesh would work the same as my RR solution would :). We've
    just solved the same question it two different ways. How didn't I
    remember confderations??? shame on me....

    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Nov 29, 2004
    #15
  16. Sandy Manning

    Ivan Ostreš Guest

    In article <cof9g7$3hl$>, says...
    > What do you mean by "logically fully meshed"? I've never heard this befor=
    > e.
    >


    Point's can be physically (with wires) and/or logically (using
    configuration commands - peers in this scenario) meshed.


    --
    -Ivan.

    *** Use Rot13 to see my eMail address ***
     
    Ivan Ostreš, Nov 29, 2004
    #16
  17. On 29.11.2004 22:19 Ivan Ostreš wrote


    > In article <cof9g7$3hl$>, says...
    >> What do you mean by "logically fully meshed"? I've never heard this befor=
    >> e.
    >>

    >
    > Point's can be physically (with wires) and/or logically (using
    > configuration commands - peers in this scenario) meshed.
    >


    IBGP peers in most cases are what you called "logically fully meshed".
    But for BGP that does not make any difference whether IBGP peers are
    physically directly connected or not. Hence to add the attribute
    "logically" is imho irritating only.




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Nov 29, 2004
    #17
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