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Community Member

Help !! OSPF problem !!

Hi,

I have some ospf problem, the attachment is network diagram :

1. SW1 is in area 0
2. SW3 & SW4 are ABR ( area 0 & area 1 )
3. SW1 have connected network 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24
4. SW2 is new switch, it also configure as area 0. it have connected network 10.1.4.0/24, 10.1.5.0/24, 10.1.6.0/24
5. SW3 & SW4 have connected network 10.2.1.0/24, 10.2.2.0/24, 10.2.3.0/24
6. SW1, SW2, SW3, SW4 have redistribute connected and static route into OSPF

While the link between SW4 & SW2 connect ( SW1 & SW2 still disconnect ), it cause hosts connect at SW1 ( 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24 ) can not access to SW4 loopback IP address. Please tell me the reason why this problem occur?

Best Regards,

Jackson Ku

8 REPLIES

Re: Help !! OSPF problem !!

Hi jackson

Is the SW1 not able to access SW4 loopback (10.2.254.2) only when  SW2 is connected ? If SW2 connection is removed, they are able to ping 10.2.254.2 ? Can you paste the show ip route 10.1.1.1 from SW 4 , and show ip route 10.2.254.2 from SW1 ? Is the link between SW3 & SW4 layer 2 ?

Raj

Community Member

Re: Help !! OSPF problem !!

Hi Raj,

Is the SW1 not able to access SW4 loopback (10.2.254.2) only when  SW2 is connected ?  Yes

If SW2 connection is removed, they are able to ping 10.2.254.2 ? Yes

Can you paste the show ip route 10.1.1.1 from SW 4 , and show ip route 10.2.254.2 from SW1 ? I have no chance to get route info at sw1 & sw4 beacuse I should recover the network immediately.

Is the link between SW3 & SW4 layer 2 ? Yes

Best Regards,

Re: Help !! OSPF problem !!

Is the link between SW3 & SW4 layer 2 ? Yes  --> You should convert this to Layer 3, as Guisseppe mentioned... his post gives you the explanation of why you would need it..

Raj

Hall of Fame Super Silver

Re: Help !! OSPF problem !!

Hello Jackson,

I've looked at your network diagram. You need a L3 link between the two ABR nodes SW3 and SW4 in OSPF area0 otherwise you have a partitioned area 0.

move one IP subnet in area 0 for example 10.2.1.0/24 and you should fix your problem: you cannot go through area 1 to reach the second half of area 0. Unless you use a virtual-link that I would avoid.

Hope to help

Giuseppe

Community Member

Re: Help !! OSPF problem !!

Hi,

The SW3 & SW4 is connected by 802.1q trunk port, but I have configure Layer 3 SVI at both SW3 & SW4 and enable OSPF routing at this L3 SVI.

I know this diagram have some problem, the area 0 is partitioned. I think the problem would not occur if I connect SW1 & SW2 first. Would you please tell me more detail why SW1 can not access to SW4 loopback IP?

Best Regards,

Jackson

Hall of Fame Super Silver

Re: Help !! OSPF problem !!

Hello Jackson,

if you have an 802.1Q trunk between the two ABRs you can add a L3 link in area 0 between the two ABRs.

Having a second link in area 0 that can avoid partitioning of area0 in case of a single link failure is good and I would do so.

So I would connect Sw1 to Sw2 and SW3 to SW4 in area 0.

Hope to help

Giuseppe

Community Member

Re: Help !! OSPF problem !!

Dear All,

Thanks a lot ...

Jackson Ku

Blue

Re: Help !! OSPF problem !!

Jackson:

I would take Giuseppe's second recommendation: Connect SW1 ro SW 2 and SW3 to SW4 with routed connections in Area 0.

Also, youve answered your own question regarding why SW1 cannot access the Lo0 address of SW4. The Area is split and there is no way for Sw4 to advertise its Lo0 address to anyone else on the network - there is no OSPF neighborship between SW4 and anyone else to be able to advertise that isolated subnet.

HTH


Victor

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