Review of draft-ietf-pwe3-segmented-pw-13 Do not be alarmed. I have reviewed this document as part of the security directorate's ongoing effort to review all IETF documents being processed by the IESG. These comments were written primarily for the benefit of the security area directors. Document editors and WG chairs should treat these comments just like any other last call comments. This document extends the pseudo-wire (PWE3) architecture by defining multi-segment pseudo-wires. A pseudowire (PW) links two Terminating Provider Edges (T-PEs). PWs are transmitted through a tunnel between the T-PEs. I'll call this a bundle of PW's. A multi-segment PW connects two bundles and (de)multiplexes the PWs to the correct tunnels. At this point I need to disclose that I have never before heard of PWs and have only a foggy notion of their purpose. I'm sorry for being ignorant. There is more to PWs than I can absorb in the time available for a review. I can, however be slightly helpful in noting that section 3.i. uses the term "cryptogtaphiclly (sic) sign" where "include a cryptographic message authenticator" is more accurate. Again, on the apology side of the ledger, I cannot follow the first example motivating the need for multi-segment PWs. Somehow, if authentication is used between two AS's, and if they use a single PW, then they would have to include an authenticator on all T-PE messages. And that is somehow bad. The second example involves a routing protocol that sets up a path involving concatenated PWs. In that case, multi-segments with switching can dynamically (?) carry the traffic between the intended T-PEs. That's good because it avoids setting up PWs for all possible paths. The third example is even harder, and in that one, multi-segment switching has the potential (why not guarantee?) of reducing the number of PWE3 control channels. The diagrams showing the evolution of the architecture from a single tunnel with a bundle of PWs to multiple tunnels and then to switched tunnels is very helpful, but I don't really see how the examples fit into it. The gist of the document is that single-segment PWs can be joined into multi-segment PWs, with all of the security problems that attend to any similar graph building procedure. The document relies on several preceding documents for exchanging control information, all of which have security considerations, all of which apparently apply to the multi-segment case. I failed to get an elemental understanding of how the signalling and control messages extend the single-segment PWs to multi-segment PWs. In section 10.3 this sentence appears to have a missing or incorrect word: However T-PE participating a MS-PW, SHOULD be able to process the S-PE TLV. The looming security problem is that the only way to make sure that connections are made correctly is to have a table of endpoints and pre-placed shared keys between them. Is this at all realistic, given that multi-segment PWs are for situations in which an organization has developed an architecture too rich for single-segement PWs? Because I don't fully understand PWs, and because the underlying protocols for exchanging control information rely on pre-placed keys, I cannot recommend anything better. I do hope that anyone using this kind of architecture is clueful and careful. Hilarie