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Re: [RAM] Tunnelling & GigE jumbo frame size

Dino Farinacci <dino@cisco.com> Wed, 12 September 2007 19:48 UTC

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From: Dino Farinacci <dino@cisco.com>
Subject: Re: [RAM] Tunnelling & GigE jumbo frame size
Date: Wed, 12 Sep 2007 12:47:58 -0700
To: Iljitsch van Beijnum <iljitsch@muada.com>
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> I guess I should read the latest LISP draft as apparently there  
> specific a jumboframe size is mentioned, and I have no idea for  
> what purpose.

To summarize the issue we are trying to put to rest:

o All router-to-router links on the downstream side of an ITR use  
either 4470 or
   9180 byte MTUs.
o We don't care about the links inside a site because a packet is not  
LISP
   encapsulated there (in the typical case of a CE deployment of LISP).
o Hosts can originate 1500 byte sized packets.
o ITRs and TE-ITRs can prepend IPv4 and/or IPv6 headers without  
worrying about
   doing PMTU discovery or fragmentation.

So even when ~80 bytes of IPv6 is used for encapsulation, we have  
enough breathing room to avoid fragmentation (in the event we have 2  
headers, one for purposes of Loc/ID separation and the other for ISP- 
based TE).

Dino

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