Thanks for the responses. To follow up this is how the offending ISP responded to our inquiries. I do not believe any further follow up is necessary.

*snip*
Thank you for getting in touch.

I am afraid an engineer made an error in the BGP configuration of one of our devices earlier this afternoon, which resulted in a number a host routes being inadvertently announced to certain of our upstream providers.

The route itself existed as part of a set of prefixes internally routed to null on our network.  This particular IP hosts a TOR relay node, and while that is perfectly legitimate we have a business requirement to block access to these internally:

https://metrics.torproject.org/rs.html#details/383D6E34D9BEA92E97092B134A708EEF476DF2E4

The route should never have been announced outside our own AS.  Unfortunately due to human error it was advertised earlier today (May 9th) from approx. 11:04 to 11:10 UTC.  I can assure you this was an unintentional error, we had no desire to interrupt or affect communications outside our AS.  The mistake was quickly spotted by our own NOC team and reverted.

I hope you can accept our sincere apologies for this issue, we have taken steps to ensure that any similar mistake will not have such impact in future.
*snip*

On Wed, May 9, 2018 at 11:54 AM, grarpamp <grarpamp@gmail.com> wrote:
On Wed, May 9, 2018 at 2:06 PM, Trevor Ellermann <trevor@ellermann.net> wrote:
> I just a notification from my data center that someone is trying to hijack
> the IP of my exit node. Seems like the sort of thing someone might do when
> trying to attack Tor. I'm in a very remote area with limited access but any
> suggestions on actions I should take?

Make sure your box and keys aren't compromised.
If that's ok, best they can do if the announcements are
listened to is camp on the ip for a while using their own keys,
(there might be some identification attacks made possible with
such a transient reroute,) circuits would fail till the consensus
updated to them, but there could be some duplicate ip split horizon
issues involved due to filtering.
If they hacked the boxes there's hardly need to expend noisy
reroutes when they can do most attacks using the box itself.

Hop on the route servers or your other favorite interfaces
to the net and analyze who all is announcing /32's trying to
cover any other tor nodes.

Sane isp's will filter such things without prior coordination. It's fairly rare,
and for them to bother giving customers courtesy reports. Though
depending on nature of ticket / relationship with GBLX, you might want
to reply saying you've never worked with Asavie and don't approve
of the action regarding your IP.

You can also search AS200005 to see what kind of heat
they catch from other operators / internet analysis tools.

> ====================================================================
> Possible Prefix Hijack (Code: 10)
> ====================================================================
> Your prefix:          204.17.32.0/19:
> Prefix Description:   GBLX-US-BGP
> Update time:          2018-05-09 12:11 (UTC)
> Detected by #peers:   1
> Detected prefix:      204.17.56.42/32
> Announced by:         AS200005 (Asavie Technologies Limited)
> Upstream AS:          AS200005 (Asavie Technologies Limited)
> ASpath:               200005
>
>
> https://torstatus.blutmagie.de/router_detail.php?FP=383d6e34d9bea92e97092b134a708eef476df2e4
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