Multiple default routes in routing table but with different metrics OSPF.

Answered Question
Jan 14th, 2010
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Multiple default routes in routing table but with different metrics OSPF.

The high-level design is two Cisco ASA firewalls, two ISPs, and two L3 core switches.

ASA A is used for outbound traffic.

ASA B is used for inbound traffic such as SMTP, Web, FTP.

ASA A connected to ISP A and ASA B connected to ISP B.

Both ASA A and ASA B connect to internal Core L3 Switches Core-1, and Core-2.

ASA A, ASA B, Core-1, Core-2 all run OSPF and learn default routes from the ASA A and B.

ASA B advertises the default route with a higher metric.

All servers belong to the same internal network.

A route map will be used to send a handful of servers to use ASA B as its primary default  gateway.

Will the route MAP send the default route to ASA B upon matching the access list for only a handful of hosts if the route is not in the routing tables of the core switches but in the OSPF database?

How can I have both default routes in the routing tables but one with a higher metric so it is never used unless the primary default route is lost but only used by the route MAP?

The L3 switches are Cisco 3560 with enhanced image.

Thanks a bunch.

Regards,

Juan

Correct Answer by Giuseppe Larosa about 7 years 3 months ago

Hello Juan,

PBR works on traffic not routes.


until the PBR IP next-hop of ASA B is seen as reachable PBR will work.


To be noted that ASA B may suppress its advertisement of an external defaul route. But again this is not a problem


Depending on your devices you should look for ways to check to verify availability of next hop.


Hope to help

Giuseppe

Correct Answer by Jon Marshall about 7 years 3 months ago

juan-ruiz wrote:


Multiple default routes in routing table but with different metrics OSPF.

The high-level design is two Cisco ASA firewalls, two ISPs, and two L3 core switches.

ASA A is used for outbound traffic.

ASA B is used for inbound traffic such as SMTP, Web, FTP.

ASA A connected to ISP A and ASA B connected to ISP B.

Both ASA A and ASA B connect to internal Core L3 Switches Core-1, and Core-2.

ASA A, ASA B, Core-1, Core-2 all run OSPF and learn default routes from the ASA A and B.

ASA B advertises the default route with a higher metric.

All servers belong to the same internal network.

A route map will be used to send a handful of servers to use ASA B as its primary default  gateway.

Will the route MAP send the default route to ASA B upon matching the access list for only a handful of hosts if the route is not in the routing tables of the core switches but in the OSPF database?

How can I have both default routes in the routing tables but one with a higher metric so it is never used unless the primary default route is lost but only used by the route MAP?

The L3 switches are Cisco 3560 with enhanced image.

Thanks a bunch.

Regards,

Juan


Juan


Not sure what you are asking here. If you are using PBR with a route-map then you override the routing table ie. you do not look for a route in the routing table at all. So if you have PBR set up for some servers with the next-hop as ASA B then it is irrelevant what is in the routing table or the OSPF database, the server traffic will still be sent to ASA B.


Is that what you were asking ?


Jon

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Correct Answer
Jon Marshall Thu, 01/14/2010 - 07:04
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juan-ruiz wrote:


Multiple default routes in routing table but with different metrics OSPF.

The high-level design is two Cisco ASA firewalls, two ISPs, and two L3 core switches.

ASA A is used for outbound traffic.

ASA B is used for inbound traffic such as SMTP, Web, FTP.

ASA A connected to ISP A and ASA B connected to ISP B.

Both ASA A and ASA B connect to internal Core L3 Switches Core-1, and Core-2.

ASA A, ASA B, Core-1, Core-2 all run OSPF and learn default routes from the ASA A and B.

ASA B advertises the default route with a higher metric.

All servers belong to the same internal network.

A route map will be used to send a handful of servers to use ASA B as its primary default  gateway.

Will the route MAP send the default route to ASA B upon matching the access list for only a handful of hosts if the route is not in the routing tables of the core switches but in the OSPF database?

How can I have both default routes in the routing tables but one with a higher metric so it is never used unless the primary default route is lost but only used by the route MAP?

The L3 switches are Cisco 3560 with enhanced image.

Thanks a bunch.

Regards,

Juan


Juan


Not sure what you are asking here. If you are using PBR with a route-map then you override the routing table ie. you do not look for a route in the routing table at all. So if you have PBR set up for some servers with the next-hop as ASA B then it is irrelevant what is in the routing table or the OSPF database, the server traffic will still be sent to ASA B.


Is that what you were asking ?


Jon

Correct Answer
Giuseppe Larosa Thu, 01/14/2010 - 07:06
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Hello Juan,

PBR works on traffic not routes.


until the PBR IP next-hop of ASA B is seen as reachable PBR will work.


To be noted that ASA B may suppress its advertisement of an external defaul route. But again this is not a problem


Depending on your devices you should look for ways to check to verify availability of next hop.


Hope to help

Giuseppe

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