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Can ISDN Backup work for a Broadband Cable modem on an Ethernet Port ?

Hi, I have the followings;

1xCisco 1721

1xS/T ISDN Port

1xEthernet Port

The above ethernet Port is connected to the Broadband (Primary Link) Cable modem.

The ISDN Link is used to backup the Primary Link.

Q1) When the Broadband link is down, is the ethernet Port Line Protocol also down ? Can the ISDN link detect that the primary link is down in this ?

Q2) If I have gateway x.x.x.x for the Primary link and gateway y.y.y.y for the ISDN link, so can I have the following static routes ?

ip route 0.0.0.0 0.0.0.0 x.x.x.x

ip route 0.0.0.0 0.0.0.0 y.y.y.y

Please clarify the routing for the Primary Link and the backup link.

Q3) How to configure a static route is higher precidence than the other ?

Anyone please help out.

Thank you...

1 REPLY
VIP Purple

Re: Can ISDN Backup work for a Broadband Cable modem on an Ether

Hello,

Q1) When the Broadband link is down, is the ethernet Port Line Protocol also down ? Can the ISDN link detect that the primary link is down in this ?

--> Yes, in case your primary connection goes down, the line protocol goes down as well. The line protocol being down is enough for the backp BRI interface to come up. Configure your primary interface with the line:

interface ethernet0

backup interface bri0

Q2) If I have gateway x.x.x.x for the Primary link and gateway y.y.y.y for the ISDN link, so can I have the following static routes ?

ip route 0.0.0.0 0.0.0.0 x.x.x.x

ip route 0.0.0.0 0.0.0.0 y.y.y.y

Please clarify the routing for the Primary Link and the backup link.

--> give the static route that points to the ISDN connection a higher administrative distance, that way you make sure that traffic is only routed through that route when the primary route is down (this is generally called a floating static route)

ip route 0.0.0.0 0.0.0.0 y.y.y.y 200

Q3) How to configure a static route is higher precidence than the other ?

--> same as in the previous question:

ip route 0.0.0.0 0.0.0.0 y.y.y.y 200

HTH,

Georg

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