Hi, Linda,

On 10/6/2016 1:34 PM, Linda Dunbar wrote:
>
> Joe and Mark,
>
>  
>
>  
>
> You said “Because tunnels are links, they are subject to the same
> issues as any link, e.g. MTU..”
>
> The MTU issue exist between any two points in a network.
>

A link MTU is different from a path MTU, as explained in the document.
The MTU issues of a link are different than those of a path, as described.


> The MTU issue for tunnel is more like the MTU issue between any two
> points in the network (i.e. traverse many links, and can change over
> time), less like the MTU for a single link because the single link MTU
> is only determined by the fixed TWO endpoints of the link, whereas the
> MTU of a tunnel (and a path) is impacted by many links in between,
> i.e. more dynamic and can change depending which path the packet
> traverse through.
>

Both a link and tunnel may have multiple hops not visible to IP, each of
which may have a different MTU; this is no different than an IP path
MTU. The difference is that the link/tunnel hops are not visible to IP.

>  
>
> In the section 1 of your draft, you stated:  “.. tunnels emulate a
> link”.  To me, “tunnel” hide the inner addresses, but the packets can
> traverse many links.  So Tunnels hardly emulate a link.
>

There are many link layer technologies which use multiple link-layer
hops and relaying, including Ethernet, ATM, SONET, etc.

Joe


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