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OSPF routing question regarding redistribution versus "network" statement

Lets say I have 5 links on my router.  Only 1 link is connected to another router.  The others are connected to L2 switches.

Which is a better choice for advertising those links?

A) Redistribute connected

B) Add "network <network> ..." statements for all the links

What are the differences between the two approaches?

Vince

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Cisco Employee

OSPF routing question regarding redistribution versus "network"

Differences IMHO...

1. Ease of Control - without a route-map the redistribute connected will advertise all connected interfaces. Network statement can configured to match all interfaces but it can just as easily be configured to match a one or set of interfaces.

2. OSPF Neighbor - network command instructs router to advertise network and send hello packets. Adding passive interface will stop the hello packets. The redistribute connected will never attempt to send OSPF hellos out those interfaces.

3. Number of LSA - redistribute connected will create an LSA for each network. With network command all links will be included in one LSA.

4. Stub configuration - if you ever wanted to configure network as stub you would need to remove the redistribute statement and configure as network statements or configure a NSSA.

5. Type 2 External LSA - For each network a type 2 external LSA is created by default. As the LSA traverses the network cost or metric is not cumulative. You would need to configure it as a type 1 to get the same effect as a summary or router LSA.

6. OSPF Path Selection - OSPF prefers networks in this order. 1. Intra-area, interarea, E1, and then E2. Cost only impacts the forwarding decision when the router is the same type of path.

Okay, that's all I can think of for the moment. Bottom line go with network. 1-2 not a big deal but I think 3-6 suggest that using network is a better choice. Disclaimer: Overall design requirements could say otherwise...

2 REPLIES
VIP Super Bronze

OSPF routing question regarding redistribution versus "network"

Have a look at this discussion

https://supportforums.cisco.com/thread/153064

HTH

Cisco Employee

OSPF routing question regarding redistribution versus "network"

Differences IMHO...

1. Ease of Control - without a route-map the redistribute connected will advertise all connected interfaces. Network statement can configured to match all interfaces but it can just as easily be configured to match a one or set of interfaces.

2. OSPF Neighbor - network command instructs router to advertise network and send hello packets. Adding passive interface will stop the hello packets. The redistribute connected will never attempt to send OSPF hellos out those interfaces.

3. Number of LSA - redistribute connected will create an LSA for each network. With network command all links will be included in one LSA.

4. Stub configuration - if you ever wanted to configure network as stub you would need to remove the redistribute statement and configure as network statements or configure a NSSA.

5. Type 2 External LSA - For each network a type 2 external LSA is created by default. As the LSA traverses the network cost or metric is not cumulative. You would need to configure it as a type 1 to get the same effect as a summary or router LSA.

6. OSPF Path Selection - OSPF prefers networks in this order. 1. Intra-area, interarea, E1, and then E2. Cost only impacts the forwarding decision when the router is the same type of path.

Okay, that's all I can think of for the moment. Bottom line go with network. 1-2 not a big deal but I think 3-6 suggest that using network is a better choice. Disclaimer: Overall design requirements could say otherwise...

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