Solved: OSPF Point-to-Point Question

josh94950 · ‎04-22-2010

Hello,

I am trying to understand the following configuration, any help would be highly appreciated.

From the destribution block we have uplinks to core , where we used point-to-point ( not sure why ) also priority and cost was configured ....will it work ?

DIST1A#sh run int t5/5

Building configuration...

Current configuration : 194 bytes

!

interface TenGigabitEthernet5/5

description Connection to CORE1B T1/5

ip address 10.8.8.61 255.255.255.252

ip ospf network point-to-point

ip ospf priority 255

arp timeout 1200

end

DIST1A#sh run int t5/4

Building configuration...

Current configuration : 194 bytes

!

interface TenGigabitEthernet5/4

description Connection to CORE1A T1/5

ip address 10.8.8.57 255.255.255.252

ip ospf network point-to-point

ip ospf priority 255

arp timeout 1200

end

DIST1B#sh run int t5/5

Building configuration...

Current configuration : 190 bytes

!

interface TenGigabitEthernet5/5

description Connection to CORE1B T2/5

ip address 10.8.8.69 255.255.255.252

ip ospf network point-to-point

ip ospf cost 255

arp timeout 1200

end

DIST1B#sh run int t5/4

Building configuration...

Current configuration : 190 bytes

!

interface TenGigabitEthernet5/4

description Connection to CORE1A T2/5

ip address 10.8.8.65 255.255.255.252

ip ospf network point-to-point

ip ospf cost 255

arp timeout 1200

end

Thanks,

josh

Giuseppe Larosa · ‎04-22-2010

Hello Josh,

>> ip ospf network point-to-point

having set the OSPF network type to point-to-point no OSPF DR election occurs on segment and so the ospf priority is not effective on this link.

the use of OSPF network point-to-point on LAN interfaces is used for fiber based point-to-point links where you know that there are only two devices and you want to save some resources by avoiding to elect one router OSPF DR and one OSPF BDR.

I think that the OSPF priority has been set as a safety measure should someone remove on both sides the ip ospf network point-to-point command it would be clear who would be elected OSPF DR on segment.

Hope to help

Giuseppe

View solution in original post

Jon Marshall · ‎04-22-2010

Josh

Not sure exactly what you query is. Basically from each distribution switch you have 2 L3 P2P uplinks to the core switches. So yoy have a routed L3 distro/core setup which is quite common. Each distro switch will see 2 equal cost paths to destinations reached via the core.

Is there something specific in the config you think might not work ?

Jon

josh94950 · ‎04-22-2010

Jon,

Thanks and you are right on distribution blocks to core, however I am confusing with the priority and cost on point-to-point interface .... is that a reason to configure in this way or ..

from Dist 1A ------------------> Core 1A Priority is setup to 255 , default cost

Dist 1A -------------------> Core 1B Priority is setup to 255 , dafault cost

From Dist B --------------------> Core 1A Cost is 255 , default priority

Dist B --------------------> Core 1B Cost is 255 , default priority

Thanks,

Giuseppe Larosa · ‎04-22-2010

Hello Josh,

>> ip ospf network point-to-point

having set the OSPF network type to point-to-point no OSPF DR election occurs on segment and so the ospf priority is not effective on this link.

the use of OSPF network point-to-point on LAN interfaces is used for fiber based point-to-point links where you know that there are only two devices and you want to save some resources by avoiding to elect one router OSPF DR and one OSPF BDR.

I think that the OSPF priority has been set as a safety measure should someone remove on both sides the ip ospf network point-to-point command it would be clear who would be elected OSPF DR on segment.

Hope to help

Giuseppe