I totally agree with everything that Mike has posted here... one thing I wanted to add is that a wireless link is only as good as it's engineered. We have many rock solid wireless links in use here - with proper engineering and ongoing maintenance we very rarely have issues. We do have some links that were not engineered to proper levels (sometimes where a business decision overrode a technical decision for example) and they do have blips every so often. Maintenance is so important after a link is established as stuff breaks, wears down, leaks, and moves.
Paul -----Original Message----- From: Mike [mailto:mike-na...@tiedyenetworks.com] Sent: September-10-09 12:35 PM To: nanog@nanog.org Subject: Re: Wireless STM-1 link Kenny Sallee wrote: > Seems everyone has focused on GE as the problem. You can quickly rule that > out by looking at interface error counters and doing PING tests from the > wireless router/device to something on the local network on both sides. If > OSPF is flapping because of missed HELLO packets then I'm thinking you have > a problem with either saturation on the link or actual wireless issues. > When PING does work what do the times look like? I'd look at static routing > for a bit (if practical) or changing your OSPF HELLO intervals to see if > that does anything. Here's a good link on troubleshooting > OSPF adjacency changes: > http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009 4050.shtml > I'd like to second the above. Wireless can, and often does, suffer from isses that other media such as copper and fiber media do not, and you need to be looking closely at the device's RF statistics (combined with your own monitoring of link rssi, error blocks, retrans, and others... you are monitoring and graphing this, yes?). Some of the variations you can expect in wireless include - Interference (if using unliscensed band gear - do NOT assume your little corner of the world doesn't have anyone else using the band occasionally!) Thermal inversion fade Water build up - especially inside of antennas and antenna elements, this can take your -36 rssi and make it drop to -86 and then all of a sudden come back in the space of 30 seconds. This can be the hardest problem to find - look at your connectors, the seal up job, anywhere they would have had to seal would be a place of penetration. Birds, trucks, anything causing occasional multipath reflections or blockage between the two sides Also it is my direct experience that wireless devices from all manufacturers also are more bug ridden and usually have far more exotic corner cases where their gear just does the wrong thing occasionally. Corrupt frames at the RF layer may not be detected due to various mac layer defeciencies, with the result being incorrect reassembly and framing of the junk as an ethernet frame and even including a valid fcs in the ethernet header but corrupt junk in the packet itself. Sometimes the RF device's own bridging tables get corrupted as a result, causing you to lose connectivity as bridge entries are relearned. There's all kinds of stuff that can go wrong here that is not your ordinary every day cisco 4-byte asn bug variety. My advice only is, be suspecious and be a good detective. Mike- ---------------------------------------------------------------------------- "The information transmitted is intended only for the person or entity to which it is addressed and contains confidential and/or privileged material. If you received this in error, please contact the sender immediately and then destroy this transmission, including all attachments, without copying, distributing or disclosing same. Thank you."
