Hi Sue,
thanks for the review. Some comments below.
On Mar 6, 2017, at 5:25 PM, Susan Hares <shares(_at_)ndzh(_dot_)com> wrote:
Reviewer: Susan Hares
Review result: Has Issues
The RTG-DIR has the categories: minor concerns or major concerns
regarding "issues", I wil differentiate my issues by this quality.
I also have editorial nits regardign under specified text.
Major concerns:
1) The security section is not sufficient for any review by the
Security area
This draft depends on IDR WG draft (ietf-idr-bgp-prefix-sid) that
defines the BGP Segment attribute. If this attribute is used with
IPv6, this simply gives more infromation about a link to a next.
However, the combination of this information with the information
passed using draft-ietf-idr-bgpls-segment-routing-epe-09 that utilizes
BGP to pass BGP topologies in BGP - requires a better security
section. BGP-LS was described to be an "information gathering"
function handled by a few routers on the edge of the network to obtain
link-state topology information. The BGP peers would carry this
information in a separate informational stream. With this constraint,
it was approved by the IESG.
well, we have now different models that have been deployed and assuming that
bgp-ls uses a separate stream is not accurate if we look what’s in the industry.
However, I take your point and I agree that more text in the security section
is required in order to emphasize that the model the draft addresses is
internal (DC and interconnected DC over a same-administration network).
draft-ietf-idr-bgpls-segment-routing-epe expands the initial concept
of BGP-LS from "information gathering" to a full-routing scheme of BGP
within BGP for data centers and for data center interconnection to the
network.
EPE defines a model where the topology of the peering point (not the network,
just the peering point) is advertised to an internal server.
This extension takes it out of the approved range of the
BGP-LS.
I don’t know what is the “approved range”. To me, bgp-ls carries topology
information. We started with lsdb, then extended to mpls-lsp's, ip tunnels,
peering points, and more will come.
The security of bgp-ls doesn’t change. It’s the boundary of the network where
bgp-ls is applied that matters.
Therefore, the security sections in both the IDR WG drafts
and this draft need to describe the new threat scenarios and describe
threat mitigation strategies for deployments.
I will add more text about the information originated by bgp-ls (or the bgp
prefix sid) and how it is intended to be consumed internally to a domain.
In addition, the information by BGP-LS
(draft-ietf-idr-bgpls-segment-routing-epe) or in draft-ietf-bgp-sid
may have privacy issues - so these need to be described the security
section.
same here. I will emphasize the deployment model and the security boundaries.
2) through-out the text you use words such as "ebgp3107" or BGP 3107
updates"
This phrase is inaccurate. The base RFC3107 support will not provide
BGP-Prefix support (as supported in bgp-idr-bgp-prefix. Some texts
goes on to clarify the addition of the BGP SID Prefix attribute. It
would be better to invent a new phrase or term.
I’ll check this out.
In section 8.1, the authors state:
"The Prefix Segement is a lightweight extension to the BGP Labelled
Unicast". As noted in my #1 major concern, this "hand-waving"
description either needs to be refined to be accurate. If the MPLS
usage only uses the BGP-Prefix label and does not extend to the
Egress, it is simplier.
the BGP Prefix SID Attribute is just an extension to a 3107 update.
However, it is not clear that is what section
8.1 is about. If 8.1 includes the
draft-ietf-idr-bgpls-segment-routing-epe, then BGP-LS addition does
have a number of prefixes and rules. The trade-off between BGP-LS +
BGP-LS SID (draft-ietf-idr-bgp-sid) handling + BGP LS egress peer
engineering draft (draft-ietf-idr-bgp-segment-routing-epe) and a
signalling protocol is more complex than the hand-wave.
Not sure I understand your point but to me the statement:
“The Prefix Segement is a lightweight extension to the BGP Labelled Unicast”
is correct because the prefix-sid is really just a new attribute. Here we’re
just talking protocol extension.
The interaction and combination between prefix-sid and epe is a deployment and
operational model that (we agreed above) requires more explanation in terms of
security.
It may be the
right choice based on current implementations and management issues,
but these need to be laid specifically.
3) Why are you defining 2-byte Private Use AS when there are plenty of
4-Byte Private Use AS (p. 5).
well, we just want to be sure we address the worse case where you only have 2
octets.
This usage increases the confusion regarding 2-byte/4-byte ASN. IDR
specifically worked on 4 byte ASN.
yes but in order to be aligned with 7938 we also take into account 2 octet ASN
and the re-usability of these numbers.
Minor concerns
1) It is not clear what happens in section 4.2.2 and figure 3-5
What happens if the traffic goes to node 3 instead of node 4 on the
ECMP path?
What happens if the traffic goes to node 8 instead of node 7 on the
ECMP Path?
Is there something missing in the stroy?
nope. This is plain segment routing. As explained in the draft, assuming that
you use the same SRGB (as recommended) a node is known through the same sid
value all along the network so ecmp becomes trivial.
2) section 4.3 - IBGP Labeled Unicast.
The phrase "iBGP3107 reflection with nhop-self" needs to be explicitly
spelled out as IBGP Route-Reflection with next-hop self.
ok
If that is
not what the authors mean, then it needs to be further spelled out.
It is unclear where the central IBGP nodes are that share fully the
information learned from the three clusters. (nodes:5-8 cluster 1,
nodes 3-4 cluster 2, nodes 9-10 cluster 3).
This section has hints of a solution, but it is miss a great deal.
Please upgrade to specific solution. A diagram might help.
yes. I’ll check this out. In short (you certainly figured it out) it’s about
using iBGP session where each node acts as a RR so to propagate to other iBGP
peers (this is what "iBGP reflection” refers to). I agree, it’s probably a bit
too cryptic.
3) Load Sharing hints (Section 7.1)
Elephant flow and mice flows are good descriptions. Flowlets and VL2
should either warrant a 1 sentence explanation that actually describes
these features in a 22 page draft, or be removed.
We have a reference for them but will add more text.
4) The lack of a manageability or operations section (TBD in version
-02) - concerns me. The operational issues may be well known to the
data centers and devices manufacturers who have implement this
specification, but this is an interoperability specification for IETF.
Some manageabilty comments should be included or a BCP pointed to.
ack.
Editorial issues:
I’ll go through all below and update the draft asap.
Thanks.
s.
#1 - The following 4 abbrevitions need to be initially expanded when
first used: CLOs (p.3), SRGB(p.6), flowlets (p. 14), and VL2 (p.
14).
#2 - page 7, section 4.2 last paragraph
Old/: assuming the IP Addresses, AS and label-index allocation
previously described, the"
New/: assuming the IP address with the AS and label-index allocation
previously described, the"
[Comma is optional]
#3 - page 14, section 7.1 paragraph 4, /(e.g. spine switch Node1)/ -
by the diagram it should be node 5-8 or an error. Please check the
number
#4 - page 17, section 8.2 paragraph 2.
Old/
This is easily accomplished by encapsulating the trafffic either
directly at the host or the source ToR node by pushing the BGP-
Prefix-SID of the destination ToR for intra-DC traffic, or border
node for inter-DC or DC-to-outside-world traffic./
New/
This is easily accomplished by encapsulating the trafffic either
directly at the host or the source ToR node by pushing the BGP-
Prefix-SID of the destination ToR for intra-DC traffic, or
the BGP-Prefix-SID for the the border node for inter-DC or
DC-to-outside-world traffic./
If this is not the correct logic, then you can reword this further.
I read it 4 or 5 times.
#5 - Adding a diagram to section 4.3 might help your description.
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