On Sun, Feb 27, 2000 at 04:42:20PM +0000, Alan Cox wrote:
> The gateway probe is tricky. You may start routing through one of the millions
> of machines erroneously shipped by vendors with routing enabled or via the
> wrong router. There is a router discovery protocol. Its less supported but a
> lot safer. Listening for OSPF/RIP/RIP2 can also do the detection sometimes.
Hm, ICMP router discovery never worked for me. From the comments in
Linux's icmp implementation I understand that this is supposed to
be handled by gated. But from my experience only very few people do,
and if they do, this rarely happens on internal routers. That's also
why you rarely observe OSPF or RIP on your department LAN etc.
> At the minimum you need to verify that the icmp time exceeded comes from a
> host which you cannot directly reach. If you can directly reach the 2nd or
> 3rd hop that errors then you have found a secondary host misconfigured as
> router, or a secondary router, and it just told you the correct router to
> use. Sometimes you'll get a redirect, sometimes you dont.
Good idea. That should also cover the case where you two routers
playing ping pong with your packets.
Concerning suggestions made by others: netprobe already does much of
this. For instamce, the initial probe just sits there passively,
listening to packets going by and trying to figure out DNS servers, the
local subnet, gateways, and NIS domain. But this is becoming increasingly
useless as more and more people start to use switching hubs.
Also, DHCP is a nice protocol, lizard does support it, and we do rely
heavily on it in our test environment, but it's really not being used very
widely (as just about every other configuration discovery protocol). For
some mysterious reason, many site admins do seem to prefer to walk around
and configure their machines manually.
As to the question whether probing the network is acceptable: Prior to
this DNS probe fuck up, I have had only positive feedback on this
feature. If customers start complaining netprobe will be removed.
I'm definitely in the mood to make it less intrusive.
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