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New Member

Using the ip alias as default gateway

Hi all,

I have a doubt regard to a configuration.

I have a router that uses as default gateway the ip alias of its own ace module.

1)How can I predict the routing? Do I have to check the static routes configured in the Admin context in order to understand how the ACE will route the traffic coming from the router?

Thanks

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Cisco Employee

Using the ip alias as default gateway

Hi Fabio,

The behavior I described only affects if you have multiple default gateways configured inside the same context.

Contexts  are completely independent from each other, so, a configuration line in  one of them (even if it's a default gateway configuration) will not  have any impact on the others. In your scenario, the default gateway  that will be used is the one configured under the context where the  traffic is arriving.

I hope this makes it more clear.

Daniel

3 REPLIES
Cisco Employee

Using the ip alias as default gateway

Hi Fabio,

The first thing to understand is that the routing will depend on the context where this alias IP is configured.

From the context point of view, more specific rules will always be chosen over the less specific ones. However, if there are two equivalent routes (for example, 2 default gateways), it is impossible to predict which of the two the ACE will choose.

The way the route to be used is done is by doing an ARP request for both gateways, and the first one to respond will be used until the ARP entry expires.

I hope this helps

Daniel

New Member

Using the ip alias as default gateway

Thanks for your response,

today I discovered the context associated with the ip alias, so now I assume that the packets will use the static route configured for that context.

Anyway I didn't understand your answer: I assume that the ace has only one mac address and assume that I have only one default gateway, using the arp request I just can check the association mac-ip address and based on this info how can I understand in which context is operating my default gateway?

Thanks for your time..

Cisco Employee

Using the ip alias as default gateway

Hi Fabio,

The behavior I described only affects if you have multiple default gateways configured inside the same context.

Contexts  are completely independent from each other, so, a configuration line in  one of them (even if it's a default gateway configuration) will not  have any impact on the others. In your scenario, the default gateway  that will be used is the one configured under the context where the  traffic is arriving.

I hope this makes it more clear.

Daniel

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