From: David Porta (David.Porta003@msd.govt.nz)
Date: Sat Dec 27 2003 - 09:26:58 GMT-3
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/ios122/122cgcr/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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