Ping - crazy frustration

LearnAsIGo · February 2007

Greetings All,

I rented some online rack time a few days ago. I practiced basic configuring on the devices but had trouble with pings - the interfaces would ping successfully (eventually).

I discovered if I waited a few minutes, then try pinging directly connected devices (router to router), it would work. Talk about frustration.

Is this normal in the real world? Or should ping work just as soon as you can bring up the interface and configure ip address?

If I were to try and answer my own question, I'd say the ping should be successfull as soon as the interface is configured - especially on directly connected interfaces.

Am I correct? close?

Thanks in advance.

EdTheLad · February 2007

Was it ethernet interfaces? If so, your local router needs to do an arp to discover the destination mac address.Was there a switched involved? If so spanning-tree could delay connectivity if portfast isnt configured and a port is brought online.
Next time try and provide some details of what the setup was.

wintermute · February 2007

I'd second a switch being involved without portfast turned on... will result in 50 second (default STP) wait after doing a no shutdown (on the router) before the switch starts forwarding traffic on the link

Tony.

EdTheLad · February 2007

wintermute wrote:

I'd second a switch being involved without portfast turned on... will result in 50 second (default STP) wait after doing a no shutdown (on the router) before the switch starts forwarding traffic on the link

Tony.

It would be 30 seconds, 15 sec for listening,15 for learning, the additional 20 second max age timer is involved only when there is an indirect link failure, which isnt included in this scenario.

wintermute · February 2007

Hmmm I just checked and this is what the Cisco Press ICND book says under portfast: Page 48.

Without portfast, each port must wait MaxAge plus twice forwarding delay, which is 50 seconds with the default MaxAge and Forward Delay settings.

The reason I was pretty sure is because I found out about portfast the hard way, ie I installed some cisco switches for the first time (had been using the routers for a while) and the pc's with Novel clients were timing out and taking almost a minute from the time the user pressed <ctrl> <alt> <delete> before they could log in... seems that the novel client was dropping the carrier on the Ethernet long enough to make the switch start the spanning tree process again. I'd previously only used Intel switches, which didn't have Spanning tree enabled by default. It wasn't until a user told me he timed it and it was just under a minute before he could log in that I twigged that it was a spanning tree issue.

Unfortunately I don't have a router and a switch which I can test but if someone would like to do a shutdown on the ethernet on a router connected to a switch, and then a no shutdown and time how long it takes for the led on the switch to turn green that would verify whether The book is wrong or right

Certainly you would think that Maxage wouldn't be necessary (logically) but from memory, it is unfortunately not the case...

EDIT: well maybe it is... from cisco I just found contradictory info which states that the port goes directly into listening then learning as Ed says.... anyone up for an experiment

Tony.

wintermute · February 2007

actually probably no need for a test, I should probably just send another email to ciscopress' feedback, to add another item to their erata

just shows that a 6 year old memory together with incorrect info in your study guide can add up to false beliefs!

Tony.

EdTheLad · February 2007

You must understand the context in which maxage is used.If you connect a pc to a switch port, the port will immediately transition from blocking to listening for (15 sec) then to learning for (15 sec) and then forwarding.In this senario it takes 30 seconds there is no MaxAge used.
If two switch ports are connect indirectly i.e. via a hub , sw1 ---hub---sw2, if the link between sw1 and the hub fails, sw2 will not be aware of the physical failure.If sw2 does not receive a bpdu from sw1 within the MaxAge, the backup port on sw2 will transition from blocking-->listening-->learning--->forwarding , so as you can see for an indirect failure it will take 50 seconds for the backup port to transition after the inital failure.

LearnAsIGo · February 2007

Whoa! Thanks all for VERY thorough replies. I must admit, am a little intimidated by onslaught of knowledge. No worries, will digest a little at a time.

Apologies for not specifying. Should have done so considering high-caliber replies. Will try to copy/paste configs in future posts.

Went back to rack time diary/logbook (was advised to keep one - it sure helps)

Nutshell:
1) Attempted basic serial interface and rip v1/v2 config.
R1(DTE) s0/0

R2 s0/0 (DCE)

2) ip address, mask, no shutdown, sh cdp neighbors

5) ping - FAILED - recheck above, ping again, got frustrated

6) moved on to config r2 s0/0 to r3 s0/0

7) Back to r1/r2 - SUCCESSFUL?!? (don't know time lapse between #6/#7)

End - verify rip v1,v2

Learned a heckuva lot here, will try to use this thread in next rack session.

Ping - crazy frustration

Comments