I have had multiple reoccurring issues with Fios and alter.net here in NYC for the past 6 months. Upon searching the web I see it's a reported problem by other users. I have 150/65 and going to multiple sites that pass traffic through alter can be extremely slow.
Talked with Verizon and they won't do anything about it. They will ask you to run a speed test through the Verizon Fios site. Of course everything checks out fine since it is one hop directly to their servers. They will say that anything else is third party and won't help.
My suspicion, though I have no facts to back it up, is they know about it but perhaps use it as a way of limiting your bandwidth. Primarily this happens on the weekends and from 11am to 1am week days. Anything that doesn't route through alter.net works at full speed.
Perhaps it is also that other ISP's pay for only a limited amount of bandwidth which jams up the highway.
I don't have enough technical knowledge to know but my traceroutes show the problem clearly.
For those users thinking about switching to Fios you should do traceroutes to the sites you most often use. If they hop through alter.net…. find another provider…….or stay where you are if it works well……
