From: Jay Hennigan (jay@west.net)
Date: Thu Dec 19 2002 - 02:47:51 GMT-3
On Thu, 19 Dec 2002, tan wrote:
> passive interface blocks rip broadcasts 255.255.255.255. What exactly is the
> mechanism here? Because the command is not routing protocol specific, I am
> curious if the mechanism is interal or external to the routing protocol
> process?
It is routing protocol specific. You specify it as part of the configuration
of the routing protocol in question.
> example
> -rip first actually generates the broadcast update to 255.255.255.255 but
> some other process kills it because the passive command (in the sense
> external to rip process) says to kill broadcasts to 255.255.255.255
> -same thing as above, but other process kills it because there is a rip
> identity marker in the header
> -rip internally does not generate broadcast at all
Analyzing this would probably mean disassemby of the IOS code, but I
would suspect a combination of the two. RIP generates the broadcasts
and sends them out all active (as in non-passive) interfaces participating
in RIP.
> The inadequacy I find with book descriptions is the focus on the result of
> passive int on a case by case routing protocol basis. Rather than say
> passive results in this or that, can we say definitively is does one thing
> since it is not a protocol specific command.
Ah, but it *is* routing-protocol specific. Just because the syntax is
similar between different protocols doesn't mean that the internals are
identical. Link-state and distance-vector routing protocols behave
differently, different types of interfaces (and sub-interfaces) behave
differently.
On what basis do you state that "passive-interface" is not a routing
protocol specific command? Think about within what section of IOS
configuration it is used.
If you're looking for a non-protocol-specific definition of the command,
I'd sum it up as an interface that is capable of participating in the
protocol but does not actively seek to exchange routing information or
updates. It's dangerous to go down this line of thinking as the command
IMHO is indeed routing protocol specific.
-- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net NetLojix Communications, Inc. - http://www.netlojix.com/ WestNet: Connecting you to the planet. 805 884-6323 .
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