Subject: (ngtrans) Configured Tunnels

From: "Pedro Revriego" <[email-masked]>
Date: Tue, 18 Apr 2000 17:24:40 PDT

Hi,

I have been looking at some implementations of configured IPv6 in IPv4 
tunnels  and most of then use a tunnel interface for each tunnel.

Would not this be a problem for a router that wants to use a lot of 
configured tunnels ?

Are there any alternative approaches that do not use an interface to set the 
tunnel ??

Best Regards,

Pedro
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From: [email-masked]
Date: Wed, 19 Apr 2000 09:34:49 +0900

>Would not this be a problem for a router that wants to use a lot of 

	we have configured 1024 tunnel interfaces with no problem in kernel.
	(there were some problem with routing daemons :-)
	does it look enough?
	freenet6.net uses 500 or some tunnel interfaces in their servers, IIRC.

	possible problem comes from tunnel lookup cost.  we'll need to
	search over these tunnels against incoming packets.  we have never
	measured possible impact/overehead with it though...

>Are there any alternative approaches that do not use an interface to set the 

	maybe special entries in routing table?

itojun

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From: Zachary Amsden <[email-masked]>
Date: Tue, 18 Apr 2000 17:50:26 -0700

> tunnels  and most of then use a tunnel interface for each tunnel.

That is most likely because a tunnel per interface is convenient to implement. 
 Multiple tunnels through the same interface is a possibility, but adds 
complexity to the interface.  It also provides a bottleneck point, over which 
you may develop locking contention.

> Would not this be a problem for a router that wants to use a lot of 

How many is a lot?  Order of magnitude changes many things.  I don't see it as 
a problem, unless the implementation is required to walk the device list for 
some common operation.  To my knowledge, no one has measured the performance 
of large tunnel configurations (in the thousands).  I'm not even sure there 
are enough islands to create such a large tunnel setup yet...

> Are there any alternative approaches that do not use an interface to set the 

You could do tunneling in user space, you could use multiple tunnels per 
tunnel device, you could add tunneling information to the routing table, ...

-- 
Zachary Amsden  [email-masked]  3-6919  31-2-510  Core Protocols