Hi Erik,
thank you for your review, pointed questions, and helpful suggestions. Please find responses in-lined tagged GIM>>.
Regards,
Greg
On Mon, May 27, 2019 at 1:35 PM Erik Kline via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Erik Kline
Review result: On the Right Track
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Document: draft-ietf-bfd-vxlan-07
Reviewer: Erik Kline
Review Date: 2019-05-27
IETF LC End Date: 2019-05-31
IESG Telechat date: Not scheduled for a telechat
Summary:
If my understanding is correct (which it may well not be), this document
places restrictions on the inner Ethernet and IP layer deployment that
previously may not have been present.
My reading if this document is that the outer IP header and the inner IP
header have the same VTEP src and dst IPs. The outer and inner Ethernet
headers have the same source MAC and may have the same dst MAC. Is this
correct?
GIM>> I think that you're right in regard to IP headers. Because the VXLAN packet is routed at the Layer 3 and not switched on the Layer 2, the DA MAC of the outer Ethernet header is the MAC of the Next Hop underlay router, not of the VTEP.
If so, this would mean that the VTEP's MAC address (or the special dest MAC)
cannot be used within the VXLAN network (or at least not on the same host.
GIM>> The dedicated MAC is to be used only as of the DA MAC in the inner Ethernet frame that includes a BFD control message..
Similarly, it appears that the VTEP's IP addresses are no longer free to
be used within the encapsulated VXLAN VNI. Do I understand this correctly?
Was this always the case?
GIM>> I believe that this specification does not add any new restrictions on how VTEPs IP addresses may be used.
If there is a document defining restrictions that VTEPs place on the
inner VXLAN segment, that might be good to reference.
Failing that, I think I would like to see some discussion of alternatives
that were rejected with reasons behind their rejection.
GIM>> Alternative encapsulations of BFD control message in VXLAN? I don't recall such discussions because the presented encapsulation of a BFD control message in VXLAN is pretty much the only possible way to do that given that VXLAN supports only Ethernet frames as its native payload. Thus anything must be Ethernet-encapsulated in VXLAN tunnels.
One possible solution might be to use "impossible" Ethernet addresses and
"impossible" IP addresses in the inner packet. For example, a source
IP address of all ones or all zeros would be very unlikely to ever be a
valid IP packet. I'm not 100% sure, but I suspect that a source MAC of
all ones would also never really be treated as valid. Clever use of
multicast IP and Ethernet addresses in the source fields might also be
sufficient to render the inner packet "invalid" in the sense that it would
never collide with legitimate traffic.
GIM>> Not using the real source IP address in the encapsulation of a BFD control message in VXLAN may create an attack vector and require an additional mechanism to bootstrap a BFD session between two VTEPs.
If I have misread this document, or VTEPs are already placing constraints
on the inner VXLAN environment similar to those above, then this review
should instead be treated as "Ready with Nits".
Major issues:
Only my concern/misunderstanding described above.
Minor issues:
None.
Nits/editorial comments:
* The document generally does a really good job of Expanding Acronyms
At First Use (EAAFU) -- very much appreciated. In section 1 though,
NVE is used without accompanying expansion, I think.
GIM>> Thank you. Updated the working version with the added expansion as Network Virtualization Endpoint.
* There is no 4.2 so maybe sections 4 and 4.1 could just be section 4.
GIM>> Agreed. Minor editorial changes to the first paragraph of Section 4.
