Are you pinging with DF set? Most PA-FE's I've seen only support an MTU of 1500 bytes.
Each device tends to also have a maximum packet size it can handle - even after fragmentation. I've seen some cheap CPE not respond to pings larger than about 8k. Brad Andy Dills wrote: > Ok, I have a weird situation that I'd like to get some input on. > > Cliff notes: > > Is the inability to get ping replies with datagrams of larger than 9216 > bytes across a 100mbps ethernet circuit an indication that the far end is > setup with an MTU consistent with jumbo frames? > > What to do if the far end swears it's set for 1500? > > > Background: > > We're in the process of turning up a new fast-e to a company located in > Equinix. We are not located in Equinix, but Level3 is, and we have Level3 > fiber in our datacenter. There are two major segments of this circuit: the > long haul to Ashburn and the cross connect in Equinix. The run at Equinix > is too long for copper, and Level3 for some reason insisted upon a copper > handoff, so Equinix supplied and installed transceivers to enable a fiber > x-con that is delivered via copper to the cage. > > In our datacenter, the ethernet circuit is connected directly via a short > copper run from Level3's space to a standard FE port on a Cisco router, > that has previously been in use and is known to be working. If it matters, > for now it's on a PA-2FEISL-TX (but will later be moved to a more current > PA when put into production...to my knowledge, even though that PA isn't > ideal, it should still work fine at lower bandwidth levels and with proper > full-duplex, etc. The previously attached customer had no problems pushing >> 30mbps, for example). > > When testing the circuit, using the cisco ping utility, with datagrams of > 9216 bytes or less, we have no packet loss. When datagrams larger than > 9216 bytes are used, we have 100% packet loss. > > Given the packet size when total failure occurs, my first reaction is that > the other company has somehow misconfigured their switch to use jumbo > frames, as if the circuit was a gig-e. > > According to the company at the far end, their device doesn't even support > jumbo frames, and other people are attached and working fine. They seem to > be quite certain the problem isn't on their end. I have a hard time not > believing them; checking the MTU is a pretty cut and dry thing, and I'm > working with senior level people at the other company, who I'm assuming > (perhaps an incorrect assumption) run and manage their international > network. > > > To narrow down the problem, we have had Level3 setup a laptop in their > cage at Equinix, attached to the interface facing our datacenter. When > testing to that, I had no packet loss with packets of any size up to the > maximum of 18024 bytes. To me this eliminates the long-haul portion from > consideration. > > We've also had Equinix double check (at the supervisor level) that the > transceivers are 10/100, hardcoded for 100 full-duplex (as is everything > else end to end). I also have a hard time believing that Equinix would > have any difficulties installing the correct model and properly configured > ethernet transceivers; Ashburn is a top notch facility with good people. > (I was hoping with my fingers crossed they had accidently installed gig-e > transceivers, or that Level3 had accidentally ordered gig-e > transceivers...no luck). > > As this has been a lingering issue for some time, I'm currently pushing > for technical reps from all of the companies involved to meet up at > Equinix, sit in a room, and figure it out. This is a bit difficult for the > other company as they don't have any real local staffing. So, I'm hoping > to come up with a solution that doesn't involve them getting on an > airplane, but it's starting to look like our only avenue of resolution. > > That said, has anybody encountered this before, or has any theories about > ways I can debug this short of having the other company (who doesn't have > local staff) visit their cage and attach a laptop facing us, to localize > the issue to either their switch or the Equinix cross connect? > > Am I likely correct in my theory that something is configured for the > jumbo frame MTU and thus response packets aren't being properly > fragmented? > > Thanks for any insight. > > Andy > > --- > Andy Dills > Xecunet, Inc. > www.xecu.net > 301-682-9972 > --- > _______________________________________________ > cisco-nsp mailing list cisco-nsp@puck.nether.net > https://puck.nether.net/mailman/listinfo/cisco-nsp > archive at http://puck.nether.net/pipermail/cisco-nsp/ -- Brad Gould, Network Engineer Internode PO Box 284, Rundle Mall 5000 Level 3, 132 Grenfell Street, Adelaide 5000 P: 08 8228 2999 F: 08 8235 6999 [EMAIL PROTECTED]; http://www.internode.on.net/ _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/