Cisco Switch - add secondary default route

[tolinrome tolinrome]

I have a layer 3 switch that is directly connected to 2 other layer 3 switches, all routed interfaces, ospf.

The main switch (switch A), is directly connected to switches B and C. In it's routing table switch A can see routes to both switches B and C and has a default route to switch B.

If I shutdown the interface on switch A that connects to switch B, it then routes to switch C and can see the LAN. However, although it routes everything to switch C, it does not have a default route, so no traffic can actually leave the LAN...go to the internet.

How can I make it where when the connection to switch B goes down, switch A will automatically insert a default route while routing through switch C?

Thanks.

[Richard Burts]

There are some things about your environment that we do not know and that impacts our ability to give good advice. If I am understanding correctly switchA switchB and switchC are all layer 3 switches. switchA connects to switchB and to switchC. switchA has a default route with switchB as the next hop. How does switchA learn this default route? Is it a static route on switchA? Does switchB advertise the default route to switchA?

Your question is how to have a secondary default route pointing to switchC. While there are potentially several ways to achieve this the most simple way is to configure a static default route on switchA with switchC as the next hop and to specify an administrative distance higher than the AD of the default route to switchB.

HTH

Rick

[tolinrome tolinrome]

Hi Rick,

Yes, you are correct in your understanding. Switch A does have a static default route to switchB. Switch B does not advertise a default route to switch A.

Thanks for the advice on the AD, I will try that a d post results.

[Richard Burts · Accepted solution]

Thank you for the clarification. If switchA has a static default route with switchB as the next hop then configuring a second static default route on switchA with switchC as the next hop and specifying a higher AD should work very well. When configuring this kind of thing I like to use 250 as the AD of the backup default route. This is higher than anything else that is likely to come up. I am confident that if you configure this that it should work.

HTH

Rick

[Richard Burts]

I am glad that my suggestions have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick

[luis_cordova]

Hi @tolinrome tolinrome 

Maybe that can be achieved with HSRP

On switch A

ip route 0.0.0.0 0.0.0.0 <HSRP virtual ip>

Then, you must determine which switch (B ir C) will be the active one and which will be the standby.

Regards