Re: BGP, TCP server-client

Hey Marco,

you're spot on. Thanks for clarifying that, I learnt another thing
about BGP today :) The only way to set the client and server is
through either the neighbor transport command, or an inbound acl, as
you already pointed out.

Cheers,
Marcel

On 14/10/2009, at 01:39 , Marko Milivojevic wrote:

> I think you are misunderstanding something from that RFC. It is very
> clear in section 8.2.x.y that every peer is both active and passive,
> unless otherwise configured. It also explicitly states that peer
> configured as active, can become either active or passive. Here is the
> exact quote:
>
> 8.2.1.1. Terms "active" and "passive"
>
> The terms active and passive have been in the Internet operator's
> vocabulary for almost a decade and have proven useful. The words
> active and passive have slightly different meanings when applied
> to a
> TCP connection or a peer. There is only one active side and one
> passive side to any one TCP connection, per the definition above and
> the state machine below. When a BGP speaker is configured as
> active,
> it may end up on either the active or passive side of the connection
> that eventually gets established. Once the TCP connection is
> completed, it doesn't matter which end was active and which was
> passive. The only difference is in which side of the TCP connection
> has port number 179.
>
> It takes some experience and practice to actually understand this, but
> let me try in a brief message.
>
> As you all have correctly observed, operation when both peers are
> active is pretty random. It's hard to determine which peer will be
> passive which will be active - and that's perfectly fine. Rare are
> occasions in which this even remotely matters. In fact, this helps
> speed things up somewhat. Given that routers will not be trying at the
> same time to establish connection (be active) and they both listen, as
> soon as one opens connection, the other will stop trying to be active
> and session is established. THERE IS NO COLLISION!
>
> In those rare cases when both try at the same time, connection
> collision occurs and section 6.8 of the RFC applies, as it was clearly
> written in the first paragraph of it.
>
> Kind regards,
> Marko.
>
> --
> Marko
> CCIE #18427 (SP)
> My network blog: http://cisco.markom.info/
>
> On Tue, Oct 13, 2009 at 09:17, Marcel Lammerse <m.lammerse_at_mac.com>
> wrote:
>> I just labbed this up and, to my surprise, I got the same results.
>> According
>> to rfc 4271, the bgp router-id should determine which side becomes
>> the
>> server and which becomes the client during a connection collision.
>> This
>> should be a deterministic process. But in my lab it made no
>> difference and I
>> got random results. Why?
>>
>> The neighbor transport command seems to lock the client/server role
>> down.
>> The passive side is the server, the active side is the client.
>>
>> On 13/10/2009, at 15:57 , Marko Milivojevic wrote:
>>
>>> Have you tried:
>>>
>>> neighbor X.X.X.X transport connection-mode active
>>>
>>> Out of curiosity - is this a lab requirement, or are you trying to
>>> do
>>> something weird in real life? :-)
>>>
>>> --
>>> Marko
>>> CCIE #18427 (SP)
>>> My network blog: http://cisco.markom.info/
>>>
>>> On Tue, Oct 13, 2009 at 03:49, ospfv2 <ospfv2_at_gmail.com> wrote:
>>>>
>>>> Hi Experts
>>>>
>>>> afaik to make bgp router as tcp client, we can set the router-id
>>>> higher or put update-source command. is that correct ?
>>>>
>>>> but i found out if we reload each of the router,sometime the client
>>>> become the server.
>>>> how to make the assigment permanent ?
>>>>
>>>> any comments ?
>>>>
>>>> thx
>>>>
>>>>
>>>>
>>>> R1# sh run
>>>> interface FastEthernet0/0
>>>> B ip address 192.168.1.1 255.255.255.0
>>>>
>>>> router bgp 100
>>>> B no synchronization
>>>> B neighbor 192.168.1.2 remote-as 200
>>>> B no auto-summary
>>>>
>>>> R1#sh ip bgp nei | in port
>>>> Local host: 192.168.1.1, Local port: 179
>>>> Foreign host: 192.168.1.2, Foreign port: 11001
>>>>
>>>>
>>>>
>>>>
>>>> R2#sh run
>>>> interface FastEthernet0/0
>>>> B ip address 192.168.1.2 255.255.255.0
>>>>
>>>> router bgp 200
>>>> B no synchronization
>>>> B neighbor 192.168.1.1 remote-as 100
>>>> B neighbor 192.168.1.1 update-source FastEthernet0/0
>>>> B no auto-summary
>>>>
>>>>
>>>> R2# sh ip bgp nei | in port
>>>> Local host: 192.168.1.2, Local port: 11001
>>>> Foreign host: 192.168.1.1, Foreign port: 179
>>>
>>>
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Received on Wed Oct 14 2009 - 18:11:18 ART