[Server-devel] Counting hops / likely costs to a node

Martin Langhoff martin.langhoff at gmail.com
Thu May 22 04:04:41 EDT 2008

I am looking at the feasibility of measuring (roughly, and cheaply)
the cost to reach the XS. Quite an interesting exercise :-)

Background: I'm fleshing out the rules of when do we attempt to
backup. Even if we see the XS, we want to know the number of hops to
it, so we can delay the backups if the hopcount is high and the backup
is low-pri.

So, "counting hops to the XS" actually seems to translate to -

 - In a simple mesh, there's no hope we'll see one. Drop dead.

 - In an AP, no hops to consider. Signal strength perhaps?

 - In an MPP mesh (such as the school mesh), we care about hops to the
MPP, and iwpriv fwt_lookup will get us the goods. Documentation says
that the hops entry is not used, but I tested it forcing hops with the
bt, and the hops were reported correctly.

Is there any good way to get the address of the MPP without regexes
over the ouput of route? ;-)

As a side note, once I forced things with the bt, latency talking to
that host shot up so the reverse-tunnelled ssh-through-nat I have
setup got utterly unusable. Probably an artifact of the baroque setup
I'm using :-)


 martin.langhoff at gmail.com
 martin at laptop.org -- School Server Architect
 - ask interesting questions
 - don't get distracted with shiny stuff - working code first
 - http://wiki.laptop.org/go/User:Martinlanghoff

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