From: Mengdi Cao (xianglingzj@gmail.com)
Date: Tue Oct 03 2006 - 02:32:00 ART
Brain,
Thanks again and I believe a lot of person knows the rules here. But we
need to understand why other than rules, especially when the rule does not
work (please have a detailed look at my example).
The OSPF DR/BDR election process, in general, will always elect the router
with highest priority as DR. But obviously in my example R5 with the
highest priority is not elected. (Please note that R5 is never rebooted nor
has interface went down. And by verifying the neighbour table it can be
confirmed that R1 never form adjacency with R2 directly.)
And more over, once set both R1 and R2 priority to 0, R2-R5 neighbour
relationship gone. Again this shows that there is some problem with this
setting. We must find some ways to correct it.
On 10/3/06, Brian Dennis <bdennis@internetworkexpert.com> wrote:
>
> As I said the spokes should have their priority set to 0 and here's
> why. If R5 is rebooted or R5's interface goes down, R1 and R2 could elect
> themselves DR since there isn't a DR on the segment, they can't see each
> other via OSPF hellos, and lastly because their priority isn't set to
> 0. When R5 comes back up, R5 sees that there already is a DR (R1 and/or R2)
> and since there already is a DR for the segment there isn't an election
> process no matter what R5's priority is set to. By setting the priority of
> spoke routers to 0 they will not participate in the DR/DBR election process
> and you will never have the problem of R1 or R2 becoming the DR.
>
> Let me state this once more for the record ;-). In a true "hub and spoke"
> network, the spokes must NOT participate in the DR/BDR election
> process. This means that their OSPF priority must be set to 0.
>
> HTH,
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
> ________________________________________
> From: Mengdi Cao [mailto:xianglingzj@gmail.com]
> Sent: Monday, October 02, 2006 8:22 PM
> To: Brian Dennis
> Cc: Cisco certification
> Subject: Re: Wired OSPF problem (IEWB lab 17)
>
> Hi, Dennis,
>
> Thanks for your reply but it seems not for my questions. My questions,
> state it simple, is.
>
> 1. Is there anything which take higher priority than "priority" itself? (
> i.e. Why R1/R2 is elected DR though R5 got a higher priority?)
> 2.How will priority setting on one spoke of a P2MP network affect another
> spoke? (i.e. Why R2 can not form adjacency once R1's priority is also set
> to 0?)
>
>
> On 10/3/06, Brian Dennis <bdennis@internetworkexpert.com> wrote:
> Short answer to this is that you need to set the OSPF proirity on the
> spokes to 0 so that they do not participate in the DR/BDR election
> process.This will ensure that the spokes never becoming DR or BDR.
>
> HTH,
>
> Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
> bdennis@internetworkexpert.com
>
> Internetwork Expert, Inc.
> http://www.InternetworkExpert.com
> Toll Free: 877-224-8987
> Direct: 775-745-6404 (Outside the US and Canada)
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Mengdi Cao
> Sent: Monday, October 02, 2006 9:14 AM
> To: Cisco certification
> Subject: Wired OSPF problem (IEWB lab 17)
>
> Hi, Everyone,
>
> Saw a really wired problem when I see this problem today in Lab17.
>
> Briefly, R1, R2 and R5 connects through FR, with R5 having a P2MP
> subinterface
>
> R5 --- R1
> |
> R2
>
> Interface configuration:
> R1:
> interface Serial0
> ip address 173.1.125.1 255.255.255.0
> encapsulation frame-relay
> no fair-queue
> frame-relay map ip 173.1.125.2 105
> frame-relay map ip 173.1.125.5 105 broadcast
> no frame-relay inverse-arp
> R2:
> interface Serial0
> ip address 173.1.125.2 255.255.255.0
> encapsulation frame-relay
> no fair-queue
> frame-relay map ip 173.1.125.1 205
> frame-relay map ip 173.1.125.5 205 broadcast
> no frame-relay inverse-arp
> end
> R5:
> interface Serial0.125 multipoint
> ip address 173.1.125.5 255.255.255.0
> ip ospf network non-broadcast
> ip ospf priority 10
> frame-relay interface-dlci 501
> frame-relay interface-dlci 502
> end
>
> OSPF is enabled on these interfaces with singel network statement
> matching
> the interface IP only.When the adjacency formed, it looks like:
>
>
> Rack1R5#sh ip ospf nei
>
> Neighbor ID Pri State Dead Time Address
> Interface
> 150.1.1.1 1 FULL/DROTHER00:01:57173.1.125.1
> Serial0.125
> 150.1.2.2 1 FULL/DR 00:01:54 173.1.125.2
> Serial0.125
>
> It seems that R2 is elected DR instead of R5, despite of the fact that
> R5's
> interface priority is 10, others are 1.
>
> More wired things comes one when I revoked the eligibility of being a
> DR/BDR:
>
> Rack1R2#conf t
> Enter configuration commands, one per line.End with CNTL/Z.
> Rack1R2(config)#int s0
> Rack1R2(config-if)#ip ospf pri 0
> Rack1R2(config-if)#^Z
> Rack1R2#
>
> Now it's R1's turn to be DR:
>
> Rack1R5#clear ip ospf pro
> Reset ALL OSPF processes? [no]: y
> Rack1R5#
> *Mar1 02:21:21.791: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.1.1 on
> Serial0.125 from FULL to DOWN, Neighbor Down: Interface down or detached
> *Mar1 02:21:21.799: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.2.2 on
> Serial0.125 from 2WAY to DOWN, Neighbor Down: Interface down or detached
> Rack1R5#
> *Mar1 02:23:27.087: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.1.1 on
> Serial0.125 from LOADING to FULL, Loading Done
> Rack1R5#
> *Mar1 02:23:32.043: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.2.2 on
> Serial0.125 from LOADING to FULL, Loading Done
> Rack1R5#sh ip ospf nei
>
> Neighbor ID Pri State Dead Time Address
> Interface
> 150.1.1.1 1 FULL/DR 00:01:58173.1.125.1
> Serial0.125
> 150.1.2.2 0 FULL/DROTHER00:01:50173.1.125.2
> Serial0.125
>
> As R5 has to be DR for P2MP network, I further revoked R1's eligibility:
>
> Rack1R1#conf t
> Enter configuration commands, one per line.End with CNTL/Z.
> Rack1R1(config)#int s0
> Rack1R1(config-if)#ip ospf pri 0
> Rack1R1(config-if)#^Z
> Rack1R1#^Z
>
> Then the thing comes to an end, R5-R2 neighbour relationship is gone
> after I
> clear the ospf processs!!
>
> Rack1R5#sh ip ospf nei
>
> Neighbor ID Pri State Dead Time Address
> Interface
> 150.1.1.1 0 FULL/DROTHER00:01:56 173.1.125.1
> Serial0.125
> Rack1R5#clear ip ospf prot
> ^
> % Invalid input detected at '^' marker.
>
> Rack1R5#clear ip ospf proc
> Reset ALL OSPF processes? [no]: y
> Rack1R5#
> *Mar1 03:57:10.795: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.1.1 on
> Serial0.125 from 2WAY to DOWN, Neighbor Down: Interface down or detached
> Rack1R5#sh ip ospf nei
>
> Neighbor ID Pri State Dead Time Address
> Interface
> 150.1.1.1 0 FULL/DROTHER00:01:59173.1.125.1
> Serial0.125
> Rack1R5#
> *Mar1 03:59:16.167: %OSPF-5-ADJCHG: Process 1, Nbr 150.1.1.1 on
> Serial0.125 from LOADING to FULL, Loading Done
> Rack1R5#
> Rack1R5#sh ip ospf nei
>
> Neighbor ID Pri State Dead Time Address
> Interface
> 150.1.1.1 0 FULL/DROTHER00:01:58173.1.125.1
> Serial0.125
>
> I checked the output of show ip ospf interface command, nothing found:
>
> Rack1R1#sh ip ospf int s0
> Serial0 is up, line protocol is up
> Internet Address 173.1.125.1/24, Area 0.0.0.0
> Process ID 1, Router ID 150.1.1.1, Network Type NON_BROADCAST, Cost:
> 64
> Transmit Delay is 1 sec, State DROTHER, Priority 0
> Designated Router (ID) 150.1.5.5, Interface address 173.1.125.5
> No backup designated router on this network
> Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
> oob-resync timeout 120
> Hello due in 00:00:20
> Index 1/1, flood queue length 0
> Next 0x0(0)/0x0(0)
> Last flood scan length is 1, maximum is 4
> Last flood scan time is 4 msec, maximum is 4 msec
> Neighbor Count is 1, Adjacent neighbor count is 1
> Adjacent with neighbor 150.1.5.5(Designated Router)
> Suppress hello for 0 neighbor(s)
>
> Rack1R2#sh ip ospf int s0
> Serial0 is up, line protocol is up
> Internet Address 173.1.125.2/24, Area 0.0.0.0
> Process ID 1, Router ID 150.1.2.2, Network Type NON_BROADCAST, Cost:
> 64
> Transmit Delay is 1 sec, State DROTHER, Priority 0
> No designated router on this network
> No backup designated router on this network
> Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
> oob-resync timeout 120
> Hello due in 00:00:11
> Index 1/1, flood queue length 0
> Next 0x0(0)/0x0(0)
> Last flood scan length is 1, maximum is 3
> Last flood scan time is 0 msec, maximum is 4 msec
> Neighbor Count is 0, Adjacent neighbor count is 0
> Suppress hello for 0 neighbor(s)
> Rack1R5#sh ip ospf int s0.125
> Serial0.125 is up, line protocol is up
> Internet Address 173.1.125.5/24, Area 0.0.0.0
> Process ID 1, Router ID 150.1.5.5, Network Type NON_BROADCAST, Cost:
> 64
> Transmit Delay is 1 sec, State DR, Priority 255
> Designated Router (ID) 150.1.5.5, Interface address 173.1.125.5
> No backup designated router on this network
> Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
> oob-resync timeout 120
> Hello due in 00:00:24
> Index 1/1, flood queue length 0
> Next 0x0(0)/0x0(0)
> Last flood scan length is 1, maximum is 8
> Last flood scan time is 0 msec, maximum is 8 msec
> Neighbor Count is 1, Adjacent neighbor count is 1
> Adjacent with neighbor 150.1.1.1
> Suppress hello for 0 neighbor(s)
> Rack1R5#
>
>
> Reviewed my final OSPF configuration, it seems also OK:
> Rack1R1#sh run | b router ospf
> router ospf 1
> router-id 150.1.1.1
> log-adjacency-changes
> network 150.1.1.1 0.0.0.0 area 0.0.0.0
> network 173.1.13.1 0.0.0.0 area 0.0.0.0
> network 173.1.125.1 0.0.0.0 area 0.0.0.0
> network 173.1.137.1 0.0.0.0 area 0.0.0.137
> !
> Rack1R2#sh run | b router osp
> router ospf 1
> router-id 150.1.2.2
> log-adjacency-changes
> area 0.0.0.23 nssa
> network 150.1.2.2 0.0.0.0 area 0.0.0.0
> network 173.1.23.2 0.0.0.0 area 0.0.0.23
> network 173.1.32.2 0.0.0.0 area 0.0.0.0
> network 173.1.125.2 0.0.0.0 area 0.0.0.0
> !
> Rack1R5#sh run | b router ospf 1
> router ospf 1
> router-id 150.1.5.5
> log-adjacency-changes
> redistribute eigrp 10 metric-type 1 subnets
> network 150.1.5.5 0.0.0.0 area 0.0.0.0
> network 173.1.125.5 0.0.0.0 area 0.0.0.0
> !
>
>
> Anybody got some hint on what is really happening?And how to correct
> this?Thanks a lot!!
>
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