From: David Porta (David.Porta003@msd.govt.nz)
Date: Sat Dec 27 2003 - 20:49:15 GMT-3
I think that your conclusion sounds correct.
Also, something else you mentioned made me think of something else.
1. The DR/BDR election process is triggered by the Interface State machine, and
not the Neighbor State machine.
2. The first purpose of the Hello packet is to identify neighboring routers, in
order to establish neighbor relationships, and later on adjacencies.
Therefore, in the NBMA networks, since the routers already "know" who their
neighbors are thanks to the static configuration of neighbor statements, by
giving a priority value to the neighbor we force the routers to exchange Hellos
immediately in order to transition to the 2-WAY state, and since all the
necessary information for the DR/BDR election was also statically configured,
the routers can immediately move on to electing the DR/BDR.
I think I am going to lab it and check it with a protocol analyser in order to
see the exact differences in the communication behaviour.
Cheers,
David
Dmitry Volkov wrote:
> Well, I read it earlier and didn't understand exactly what did they mean...
> DR/BDR election starts after 2-WAY state established - i.e. after each
> router received neighbor's hello with priority inside (state INIT)
> and after each router got hello from neighbor with his own RID (state
> 2-WAY). This is true whenever priority configured or not.
>
> > "When the router first starts up, it sends only hello packets
> > to those routers
> > with nonzero priority,
>
> This is partially true. Word "ONLY" here is not correct
> When we configure "neighbor x.x.x.x" (i.e. with prior 0) and reload router,
> it doesn't send any hellos within wait interval (120 sec on non-broad) after
> that router starts sending each hellointerval (30 sec on non-broadc) within
> 120 sec until dead timer expired and later sending each poolinterval (120
> sec on non-broadcast)
> when we configure "neighbor x.x.x.x priority > 0" it starts sending hellos
> upon startup until dead interval expired (120 sec on non-broadc) and after
> that continue to send each poolinterval (120 sec on non-broadc)
>
> Since we usually configure "neighbor x.x.x.x" on Hub and "ip ospf priority
> 0" on Spoke's interface or "ip ospf priority >1" on Hub interface, nothing
> happens within first 120 sec on NBMA after hub came on-line (spoke doesn't
> send anything to hub because it doesn't have neighbor configured) and only
> after wait interval expired hub sends hello to spoke, receive reply, etc.
>
> So, "weird" conclusion comes in mind:
> looks like to expedite process of building adj between hub and spoke
> "neighbor x.x.x.x priority >0" has to be on BOTH (to be able to send hellos
> upon startup) hub and spoke and NO "ip ospf priority 0" on spoke's interface
> (default "1") and something >1 priority on hub's interface. This way
> whenever hub or spoke come on-line hello exchanges happens immediately.
> Because it's not very scalable - to put something on spokes - at least
> "neighbor x.x.x.x priority >0" has to be on Hub and "ip ospf priority >1"
> also on Hub.
>
> Any comments ??
>
> Dmitry
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On
> > Behalf Of David Porta
> > Sent: Saturday, December 27, 2003 7:27 AM
> > To: Dmitry Volkov
> > Cc: 'Mike Williams'; 'P729'; 'Bob Sinclair'; 'Ashok Verma
> > (ashoverm)'; ccielab@groupstudy.com
> > Subject: Re: OSPF in NBMA networks
> >
> >
> > Hello everyone,
> >
> > I think I understand the purpose of the optional priority
> > value on the neighbor
> > command.
> >
> > Please refer to the following link on your Doc CD and under
> > "Usage Guidelines"
> > read paragraph 4:
> > http://127.0.0.1:8080/cc/td/doc/product/software/ios122/122cgc
> > r/fiprrp_r/1rfospf.htm#xtocid31
> >
> > "When the router first starts up, it sends only hello packets
> > to those routers
> > with nonzero priority, that is, routers that are eligible to
> > become designated
> > routers (DRs) and backup designated routers (BDRs). ... "
> >
> > This is what understand:
> > In an effort to expedite the DR / BDR election process and
> > adjacency formations
> > with them on NBMA networks when routers first start up, we
> > can specify the
> > neighboring router's priority value on the neighbor statement.
> > This way, when the router boots up and loads the OSPF
> > configuration, the router
> > does not have to wait for Hello's to be sent to it in order
> > to know the
> > priority value of its neigbors, plus the wait timer to expire
> > before commencing
> > the DR / BDR election process.
> >
> > Therefore the priority option on the neighbor command is
> > meant to fill in the
> > priority value information for the neighbors as soon as it
> > boots up, instead of
> > waiting for this value to arrive from the Hello packets, and
> > move on with the
> > adjacency formation process with the DR and BDR.
> >
> >
> > What do you guys think?
> >
> >
> > Cheers,
> > David.
> >
> >
> >
> > Dmitry Volkov wrote:
> >
> > > routers send their own priority to each other inside hello packets.
> > > there is no way that one dictates to another what priority
> > is should have.
> > > one router can't alter priority of other router.
> > > there is also no way that one can alter priority it
> > received from other
> > > let say A------B
> > > B's interface has default priority "1"
> > > You configure on A: neighbor x.x.x.x priority 10 (where
> > x.x.x.x - ip of B's
> > > interface)
> > >
> > > when You do "sh run" immediatelly after You did put neigbor
> > statement You
> > > will see exactly what You did configure
> > > and "sh ip ospf nei" shows configured priority but as soon
> > A received hello
> > > packet from B - everything is reverted back
> > >
> > > Dmitry
> > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On
> > > > Behalf Of Mike Williams
> > > > Sent: Saturday, December 27, 2003 12:53 AM
> > > > To: 'Dmitry Volkov'; 'P729'; 'Bob Sinclair'; 'Ashok Verma
> > (ashoverm)'
> > > > Cc: ccielab@groupstudy.com
> > > > Subject: RE: OSPF in NBMA networks
> > > >
> > > >
> > > > Is it possible that by specifying a priority with the
> > neigbor command
> > > > that it's overriding the priority that's being sent? I know this
> > > > doesn't seem to make sense as it would be silly to do so, but
> > > > possible?
> > > > Otherwise, I'd agree that there's really no reason to specify the
> > > > priority on the neighbor command (not only no reason to
> > > > specify, but no
> > > > reason for Cisco to even have that command as a option
> > unless there's
> > > > *some* functionality, although it wouldn't be the first time =)
> > > >
> > > > Mike W.
> > > >
> > > > -----Original Message-----
> > > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > > > Behalf Of
> > > > Dmitry Volkov
> > > > Sent: Friday, December 26, 2003 10:24 PM
> > > > To: 'P729'; 'Bob Sinclair'; 'Ashok Verma (ashoverm)'
> > > > Cc: ccielab@groupstudy.com
> > > > Subject: RE: OSPF in NBMA networks
> > > >
> > > >
> > > > Ok. This is all true. But what is the purpose of such
> > "indication" ??
> > > > Surprisingly enough that Syed Faraz Shamim - author of
> > > > "Troubleshooting
> > > > IP routing protocols" also follows Doyle's "mistake"
> > (page 557-558)
> > > > http://www.cisco.com/en/US/tech/tk365/tk480/technologies_confi
> > > > guration_e
> > > > xamp
> > > > le09186a0080094054.shtml#4
> > > > router ospf 1
> > > > network 1.1.1.0 0.0.0.255 area 0
> > > > neighbor 1.1.1.2 priority 2
> > > > !--Used to manually configure neighbors and assign
> > > > the priority. In case of a Hub and Spoke topology,
> > > > the Hub should be elected as the DR as it has
> > > > connectivity to all the spokes. This can be done
> > > > by assigning higher priority to the Hub using the
> > > > neighbor command on the Spoke routers
> > > >
> > > > Dmitry
> > > >
> > > > > -----Original Message-----
> > > > > From: nobody@groupstudy.com
> > > > [mailto:nobody@groupstudy.com]On Behalf Of
> > > >
> > > > > P729
> > > > > Sent: Friday, December 26, 2003 2:24 PM
> > > > > To: Bob Sinclair; Ashok Verma (ashoverm); ccielab@groupstudy.com
> > > > > Subject: Re: OSPF in NBMA networks
> > > > >
> > > > >
> > > > > Great explanation Bob. Another clue is there is no
> > provision in the
> > > > > OSPF Hello protocol for telling a neighbor what the neighbor's
> > > > > priority should
> > > > > be. You only indicate what your own priority is.
> > > > >
> > > > > Happy holidays,
> > > > >
> > > > > Mas Kato
> > > > > https://ecardfile.com/id/mkato
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Bob Sinclair" <bsin@cox.net>
> > > > > To: "Ashok Verma (ashoverm)" <ashoverm@cisco.com>;
> > > > > <ccielab@groupstudy.com>
> > > > > Sent: Friday, December 26, 2003 8:03 AM
> > > > > Subject: Re: OSPF in NBMA networks
> > > > >
> > > > >
> > > > > > Ashok,
> > > > > >
> > > > > > What you are seeing is common and probably not a "bug".
> > > > > >
> > > > > > Much of the documentation seems to say that you can control
> > > > > the priority
> > > > > of
> > > > > > a neighbor with this command. But the command docs
> > > > > actually say that the
> > > > > > neighbor priority command "indicates the router priority
> > > > > value of the
> > > > > > nonbroadcast neighbor associated with the IP address
> > > > specified". In
> > > >
> > > > > > practice, it "indicates" the same way a speedometer
> > > > "indicates" your
> > > > > speed:
> > > > > > it shows but does not determine.
> > > > > >
> > > > > > Even Doyle seems to say that you can control a neighbor's
> > > > > priority with
> > > > > this
> > > > > > command, but I have never seen it actually work.
> > > > > >
> > > > > > In practice, you will find that only entering the priority
> > > > > on the local
> > > > > > interface will actually determine a priority. You will
> > > > > also find that the
> > > > > > local neighbor priority command reflects the priority
> > > > > configured on the
> > > > > > remote neighbor interface, and will change with it.
> > > > > >
> > > > > > HTH,
> > > > > >
> > > > > > -Bob Sinclair
> > > > > > CCIE #10427, CISSP, MCSE
> > > > > > www.netmasterclass.net
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: "Ashok Verma (ashoverm)" <ashoverm@cisco.com>
> > > > > > To: <ccielab@groupstudy.com>
> > > > > > Sent: Friday, December 26, 2003 5:20 AM
> > > > > > Subject: OSPF in NBMA networks
> > > > > >
> > > > > >
> > > > > > > Hi All
> > > > > > >
> > > > > > > I have a query about NEIGHBOR command, which is used in
> > > > > the NBMA network
> > > > > > > to make the ospf peering
> > > > > > >
> > > > > > > When we define the #neighbour x.x.x.x priority 0
> > > > > > >
> > > > > > > What is the priority 0 means . Is it mean the other side
> > > > > router can not
> > > > > > > become the DR .
> > > > > > >
> > > > > > > One more observation I have is even if configure the #
> > > > > neighbour x.x.x.x
> > > > > > > priority 0
> > > > > > >
> > > > > > > When I check the configuration I see it as #neighbour
> > > > > x.x.x.x priority 1
> > > > > > > .....is it a bug ?
> > > > > > >
> > > > > > >
> > > > > > > Thanx
> > > > > > >
> > > > > > > Ashok Kumar Verma
> > > > > > > CCIP,CCDP,CCNP
> > > > > > > Network Consulting Engineer
> > > > > > > Customer Advocacy Advanced Service Dep.
> > > > > > > Service Provider AS Div.2
> > > > > > > Cisco Systems, K.K.Japan.
> > > > > > >
> > > > > > > Tel: +81-3-5324-4583
> > > > > > > e-mail: ashoverm@cisco.com
> >
> >
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