OSPF default-info originate 'metric-type 1' vs 'always'

Answered Question
Feb 26th, 2010
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Hi,


In my production routers under the router ospf 1 process there is the configuration "default-information originate metric-type 1".


In lab I tried to change this and experiment with "default-information originate always" instead and apparently the result was the same (my other OSPF routers in the domain got a default route and from there devices were able to reach the destination).


Can someone explain in practical terms the different between the two options please? If I have 'metric-type 1' in production and I will change my routing to external path from static to dynamic I want to make sure that I do not need to change this to 'originate always'.


Regards,


Marlon

Correct Answer by Jerry Ye about 7 years 3 months ago

The always keyword means to advertise the default route regardless of  whether the software has a default route.


Let's say you have ip route 0.0.0.0 0.0.0.0 x.x.x.x and assuming x.x.x.x is directly connected neighbor. When x.x.x.x is not reachable, the default will be withdraw from the routing table, with out the always keyword, the 0.0.0.0 0.0.0.0 will not be present in OSPF.


The metric-type 1 keywork is really set it to E1 (metric will be changed across the network), instead of the default E2 (metric-type 2), where the metric is the same through out of your OSPF domain.


http://www.cisco.com/en/US/docs/ios/iproute_ospf/command/reference/iro_osp1.html#wp1012794


HTH,

jerry

Correct Answer by Jon Marshall about 7 years 3 months ago

news2010a wrote:


Hi,


In my production routers under the router ospf 1 process there is the configuration "default-information originate metric-type 1".


In lab I tried to change this and experiment with "default-information originate always" instead and apparently the result was the same (my other OSPF routers in the domain got a default route and from there devices were able to reach the destination).


Can someone explain in practical terms the different between the two options please? If I have 'metric-type 1' in production and I will change my routing to external path from static to dynamic I want to make sure that I do not need to change this to 'originate always'.


Regards,


Marlon



Marlon


default-information originate will originate a default-route to neighboring OSPF routers if there is a default-route in the routing table.


default-information originate always will originate a default-route to neighboring OSPF routers even if there is no default-route in the routing table.


So if you hve an OSPF router originating the default-route but you only want it to do this as long as it has a default-route to use then you would not add the "always" option.


Jon

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Correct Answer
Jon Marshall Fri, 02/26/2010 - 13:32
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news2010a wrote:


Hi,


In my production routers under the router ospf 1 process there is the configuration "default-information originate metric-type 1".


In lab I tried to change this and experiment with "default-information originate always" instead and apparently the result was the same (my other OSPF routers in the domain got a default route and from there devices were able to reach the destination).


Can someone explain in practical terms the different between the two options please? If I have 'metric-type 1' in production and I will change my routing to external path from static to dynamic I want to make sure that I do not need to change this to 'originate always'.


Regards,


Marlon



Marlon


default-information originate will originate a default-route to neighboring OSPF routers if there is a default-route in the routing table.


default-information originate always will originate a default-route to neighboring OSPF routers even if there is no default-route in the routing table.


So if you hve an OSPF router originating the default-route but you only want it to do this as long as it has a default-route to use then you would not add the "always" option.


Jon

Correct Answer
Jerry Ye Fri, 02/26/2010 - 13:36
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The always keyword means to advertise the default route regardless of  whether the software has a default route.


Let's say you have ip route 0.0.0.0 0.0.0.0 x.x.x.x and assuming x.x.x.x is directly connected neighbor. When x.x.x.x is not reachable, the default will be withdraw from the routing table, with out the always keyword, the 0.0.0.0 0.0.0.0 will not be present in OSPF.


The metric-type 1 keywork is really set it to E1 (metric will be changed across the network), instead of the default E2 (metric-type 2), where the metric is the same through out of your OSPF domain.


http://www.cisco.com/en/US/docs/ios/iproute_ospf/command/reference/iro_osp1.html#wp1012794


HTH,

jerry

Marwan ALshawi Sun, 02/28/2010 - 01:15
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in short

to combine the two valuable comments above


the command you have in your router has 2 important things:

first there is no always keyword this means that your router must have a default route learned through any other routing protocol or a static route


second the metric type 1: the default is type 2 however type 1 if preferred in OSPF in this case if you have another router in your network and generating default route with the default metric which is 2 then the one with metric type 1 will be the primary and the other one will be the secondary


good luck

if helpful Rate

huangpo2005 Mon, 03/01/2010 - 06:58
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Have some points to add:

In ospf stub area and Totally stub area,the ABR and ASBR will announce default route automatic.

But on NSSA ABR,you should use "default-information originate" but without additional default route to announce default route.

      on NSSA ASBR ,you should use "default-information originate+default route" or "default-information originate always" to announce default route.


Metric type 1:  external metric+internal metric

Metric type 2:  external metric only   (OSPF default option)


Sky.h

Best regards!

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