[xcp] Notes from XCP meeting at ISI
faber at ISI.EDU
Fri Feb 20 15:20:31 PST 2004
On Fri, Feb 20, 2004 at 01:57:01PM -0800, Bob Braden wrote:
> 19 Feb 2004 XCP Meeting at ISI
> * Checksums
> -- Clarified how TCP checksums currently work with XCP.
> -- Ted's FreeBSD code does not support hardware checksumming.
"Does not support" is vague. The current implementation doesn't get any
benefit from the checksumming hardware, but it dosn't cause all packets
that are hardware checked to be dropped, as a naive implementation
would. I also believe that it's straightforward to support the hardware
checksum directly, now that I've thought about it.
> * Detecting Non-XCP routers
> -- It will be important to detect non-XCP routers
> in the path. For this purpose, we need a TTL field in the
> XCP header. It will be initialized to the IP TTL, and
> each router's XCP will decrement it. If there are only
> XCP routers, its value at the receiver will match the TTL
> in the IP header.
> -- This does not quite work with MPLS; something special has to
> be done. MPLS does not decrement the IP TTL, but
> XCP-capable MPLS hops might decrement the XCP TTL.
> Have to teach an XCP-capable MPLS router to not do
That doesn't really reflect the considerable debate on your suggested
TTL field. I'm far from sold, as I don't think it solves any corner
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