Re: RFC 1918

["Steven M. Bellovin" <smb () research att com>]

In message <20000714155415.K19521 () oven com>, Bennett Todd writes:
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> 2000-07-14-15:47:22 Steven M. Bellovin:
> > No -- 1918 addresses would only break PMTU if folks did ingress or
> > egress filtering for 1918 addresses.
>
> Wouldn't RFC 1918 addrs on router links only threaten to break
> PMTU --- even in the face of 1918 addr filtering --- if one of
> the routers with an rfc 1918 interface addr did routing between
> interfaces with different MTUs? As best I can see, PMTU discovery
> should work fine traversing RFC 1918 links, and the only addrs
> that need to be passed on out are those of routers where the MTU
> decreases along the path, which would only be routers with different
> MTUs on different interfaces.

Yup.  And with most links handling 1500-byte MTUs or above, we don't 
see much of that.

                --Steve Bellovin