Spelling: PeopleCantConfigureTheirRoutersMagazine
OSPF, BGP, bah. If you're reading this, you probably like one or the
other. Fuck you. They're both shit. But Ja-aymz, I hear you cry, how
can you make this assertion? * BGP is optimised for the sort of static
network that we do not have. There is a good reason why the internet
requires micromanagement to the point of insanity - BGP doesn't
actually give each host an accurate picture of the network. Which is
fine, if you're not trying to create a city wide wireless network....
there is a neat little test case on our network _right now_ that I can
use to prove this, if only I could be fucked drawing the diagram. But
consider clusters that are connected to major routers at each end,
rather than one single backbone connection. And of course TCP stalls
are fun, since most people aren't using a wifi friendly implementation
such as tcp_westwood (shame on you!). If you are into micromanagement,
though, it does at least allow you to override other dumb fucks config
choices. And if you don't, then you're fucked, because it requires it
to work _at all_. * OSPF is a fragile motherfucker, falling apart at
the drop of an elephant. It theoretically works, but in reality it
falls apart quicker than you can say "I thought bgp was going to save
the world!". And this is ignoring the fact that area 0 has all of the
downsides of BGP, with none of the good sides. OSPF implementations
completely fail to interoperate without massaging, and indeed the
default settings of most of them are total shite anyhow. One single
dumb fuck can destroy the entire network with a stupid config choice.
This is not a theoretical attack - this has happened before. Requires
less micromanagement than BGP, which is great, but doesn't provide the
capability to do the management that you _do_ need to do. Word! ----
Looking out a dirty old iface, down below the cars in the city go
rushing by I sit here alone, and I wonder why Bight lights, the music
gets faster, checking your timestamp, another glance I'm not leaving,
no honey, no not a chance. ---- I realise that this is a terribly,
terribly difficult thing for people to grasp, but this is important -
despite the name, and the shitty attempt to emulate it, WIFI IS NOT
FUCKING ETHERNET. It is ESPECIALLY not cat-5 connected ethernet, not
even 10M, let alone the 100M that everyone is trying to pretend that
it is. Today's proposed alternative is OLSR OLSR is not perfect.
It\'s not even good. It\'s got massive problems, in fact, which we\'ll
talk about here. But yet, most of those problems exist in
functionality that OSPF and BGP don\'t even provide. OLSR has three
major advantages over the aforementioned two: It was designed for mesh
routing, which vaguely resembles what we\'re trying to do, it supports
both single hosts and networks, and has at least some measure of link
quality built into it. And, unlike BGP or OSPF, a human can actually
configure the thing - even on windows. --- # A very complicated
configuration. Sort of. The actual # running config on
hanuman.nodefus.wireless.org.au # (10.10.64.130, 10.10.64.33,
10.10.48.28 [1] # # Note the special case for the ethernet
connections! DebugLevel [2] 0 ClearScreen [3] yes LinkQualityLevel [4]
2 LinkQualityWinSize [5] 100 UseHysteresis [6] no Hna4 Interface
"eth0" "wlan1" "wlan0" LinkQualityMult [11] 10.10.64.132 10.0
LinkQualityMult [12] 10.10.64.134 10.0 } LoadPlugin [13]
"olsrd_httpinfo.so.0.1" --- One of the most glaring problems is the
link quality calculation - the algorythm is 1/(packetLoss *
packetLossBackToMe). Note any mention of speed in there? I didn't
think you did... our original thought was to combine it with the
script from last month for calculating speed, and apply the output of
that to LinkQualityMult [16] - which would work great, if only you
could reconfigure the router at runtime. But, alas, you cannot. There
is a plugin interface, and this was our next thought - however, while
it can fuck with the route table, it doesn't seem to be able to change
actual settings. Which is a shame for other reasons that we'll get to
momentarily. The point is, that you need to either know your link
speed in advance, or trust that it knows best. And while on wifi
packet loss is actually a pretty good metric, it is far from perfect -
some combinations of interface are just inherently better than others.
There is an argument that the algorythm is also not harsh enough to
lossy links - a link with 30% packet loss in each direction will get a
route cost of 2.04, whereas in reality that link is almost dead. We
actually did experiment with changing the algorythm to
1/(packetLoss^2*packetLossBackToMe^2), which gave results that I was
happier with. Which is not to say that the current results are
terrible, just that they only consider the GHO link as a 1.41 cost
right now, whereas a perfect wifi link is a 1.0 cost. Under the
squared algorythm, that cost would be over 2.0, which is much more
realistic. But I really don't want to maintain a forked tree -
especially considering that pre-built binaries already exist for
linux, windows, pocketpc, and wrt54g. I'm sure that few would argue
this point. The other major complaint, is that point to point links
are non-obvious. UDP is the transport used, although unlike OSPF the
unreliable transport actually works well here. But the default is to
send to the broadcast address of the network - the official way to set
up point to point exclusive links, is to change a parameter called
Ip4Broadcast. Which makes sense when you think about it, but is non
obvious. I don't think you can have multiple ones of these per
interface, either, especially a problem when due to other trivia,
olsrd tends to fail with aliased interfaces. Ironically, in the name
of sanity checking. There is no management, the program knows best.
This is a horrible pain in the ass sometimes... like now, for example.
Of course, there is an argument that most MW people shouldn't be
controlling their routers in the first place. The protocol is designed
to be self configuring, and sometimes this even works. It's just a
pain when it doesn't. And like I said, if you don't like it, who the
fuck want sto maintain a parallel version? Not fucking me. But still,
the question is, better than OSPF though? Almost certainly. Better
than BGP? No, except if you're trying to do what we're trying to do.
Then Yes.
Links:
------
[1] http://olsr.org).
[2] http://melbournewireless.org.au/?DebugLevel
[3] http://melbournewireless.org.au/?ClearScreen
[4] http://melbournewireless.org.au/?LinkQualityLevel
[5] http://melbournewireless.org.au/?LinkQualityWinSize
[6] http://melbournewireless.org.au/?UseHysteresis
[7] http://melbournewireless.org.au/?HelloInterval
[8] http://melbournewireless.org.au/?HelloValidityTime
[9] http://melbournewireless.org.au/?HelloInterval
[10] http://melbournewireless.org.au/?HelloValidityTime
[11] http://melbournewireless.org.au/?LinkQualityMult
[12] http://melbournewireless.org.au/?LinkQualityMult
[13] http://melbournewireless.org.au/?LoadPlugin
[14] http://melbournewireless.org.au/?PlParam
[15] http://melbournewireless.org.au/?PlParam
[16] http://melbournewireless.org.au/?LinkQualityMult
[EditText] [Spelling] [Current] [Raw] [Code] [Diff] [Subscribe] [VersionHistory] [Revert] [Delete] [RecentChanges]