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New Member

Discontigous OSPF Areas

Dear All,

One of our customer have following OSPF setup,

R1(Area1)---(Area1)R2(Area0)----(Area0)R3(Area1)----(Area1)R4

Link b/w R1 & R2 is in area 1.

Link b/w R2 & R3 is in area 0.

Link b/w R3 & R4 is in area 1.

and there is a direct link between R1 & R4 as well. Customer wants to disconnect this link so in this case Area 1 will become discontigous. I setup this in a lab environment and found that routes are exchanging between R1 & R4 properly using their respective ABRs i.e R2 & R3 respectively. But routes from each discontigous part of Area 1 are installing as Inter Area routes into routing table of R1 & R4. My question is that what could be the consequences of running OSPF in this type of setup.

Regards,

Mujeeb

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: Discontigous OSPF Areas

Mujeeb,

As it is allowed by the OSPF spec, it is very common practice and doesn't cause any specific issue.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
3 REPLIES
Cisco Employee

Re: Discontigous OSPF Areas

Mujeeb,

This is indeed the expected behavior. OSPF allows for non-backbone areas to be discontiguous and for routing updates between these areas to be propagated via the backbone area, hence these routes being seen as Inter-Area.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Discontigous OSPF Areas

Hi,

From design perspective , it could create some problem in production network ??

Regards,

Mujeeb

Cisco Employee

Re: Discontigous OSPF Areas

Mujeeb,

As it is allowed by the OSPF spec, it is very common practice and doesn't cause any specific issue.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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