Interface Flapping

[ChrisAC]

Could someone settle this!

We installed a router on a customers site, but at the moment it's not being utilised! Ok! The serial interface is plugged into the NTE and the port is UP. The ethernet interface is not yet patched into the network as the customer is still putting their network together.

Now, the ethernet interface has an IP address but the serial interface is "unnumbered eth0". So, back in the office we can't ping the router as the ethernet interface is down. Our core guys tell us that the serial interface is flapping and it's a problem. We say that it's normal as there is no traffic being sent over the link 'cos eth0 is down. We've had this before and it's always okay when eth0 comes up.

Any comments?

Chris.
********************************
Chris Andrew, CCNA
Technical Support Engineer
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[hexn]

I think you are stuck. You arent going to be able to access that router till you get that ethernet interface up. I dont know why they cant just plug it into a hub just for the sake of bringing it up.

Also, just shut down the serial interface on your side till they tell you it is up. It wont hurt anything. ~~~~~~~~~~~~~~

tech@shnypr.com

http://shnypr.com/tech

~~~~~~~~~~~~~~

 

[wybnormal]

For starters, best practices is to use unnumber interfaces with a loopback address that wont go down.. even if the ethernet is not plugged in, you can fool it by using the keep alive commands to fake it out. Your log will get a ton of error messages but it will "come up" or so it thinks. See the CCIE Study Guide from McMillian for examples of this.

MikeS
Find me at

http://www.packetattack.com

"Diplomacy; the art of saying 'nice doggie' till you can find a rock" Wynn Catlin

 

[ChrisAC]

Cheers guys!

So, let me get this right!! The Serial interface can't use the IP of the ethernet interface while the ethernet interface is down! The question is, can the serial interface send out keepalives to the core router and therefore keep the line protocol up while eth0 is down? Or, if it can't get it's IP address from eth0, then it can't send out keepalives??

We know that it can't get it's IP address while eth0 is down, otherwise we'd be able to telnet to it! I'm just curious as to how the keepalives work in this situation!!

I think that I'll take a router into the lab on Monday morning and check it out!!

Chris.
********************************
Chris Andrew, CCNA
Technical Support Engineer
********************************

 

[ShaunG]

If you put in a no keepalive statement under your ethernet or serial interface then it won't expect to get them. This will bring the interface up/up and keep it that way whether it is plugged in to another device or not.