Hi, Richard:
发件人: alto [mailto:[email protected]] 代表 Y. Richard Yang
发送时间: 2022年9月14日 1:47
收件人: IETF ALTO <[email protected]>
主题: Re: [alto] ALTO service query spanning multiple domains (ECS)
Hi all,
There were quite extensive discussions, on the reactive/on-demand, multi-domain
design below, during the weekly meeting early this morning and here is a brief
summary of the key points.
- The design can be decomposed into two components: routing composition and
cost metric composition, from single domains to multiple domains:
(metricVal, egressIP) = alto-server.query(ingressIP, srcIP, dstIP, metric)
[Qin Wu] I feel this formula doesn’t explicitly indicate this is multi-domain
setting, when srcIP and dstIP belong to different domains, we need to calculate
ingressIP and egressIP in each domain one by one, also metricValue is not end
to end metric, it is edge to edge metric.
=>
egressIP = query(ingressIP, pkt-attributes) // Q1
metricVal = query(ingressIP, pkt-attributes, metric) //Q2
- It turns out that there can be at least multiple potential design points:
For Q1: It can have two designs:
- D1.1 It can be that Q1 is out of scope for ALTO, for example, by using a
routing system to conduct the query
[Qin Wu] if each alto server can calculate edge to edge metric from ingress
node to egress node in each domain, why bother routing system to conduct the
query, the routing system can provide measurements and inject measurement
results to alto server. No?
- D1.2 It can be a new service/metric type in ALTO
[Qin Wu] yes, you can introduce new service/metric type in ALTO, we have
already define similar service/metric type in PCE, see RFC8233.
In addition, as I clarified in the previous email, we need to distinguish
server to server communication within a domain and one across domains, this
require ALTO protocol extension, e.g., inter-domain flag indication, I am not
sure stitching label is required,
In PCE use case, stitching label is required to setup end to end path across
domain.
For Q2: it also can have two designs:
- D2.1 using the current RFC7285 for Q2, with specifying ingressIP as src,
in the ECS query
This design is good if a network is destination-based routing
- D2.2 We add an extension to ALTO ECS, to include general packet (and
pseudo packet) attributes
For the extension design path, it can help to
(1) convey the matching requirements in the IRD (for example, what packet
attributes to be included)
(2) return indicates the equivalent classes (matching masks).
[Qin Wu] I am not sure caching is required in this case, I am worried about
matching masks might be error prone. I suggest to investigate how
Backward-Recursive PCE-Based Computation (BRPC) Procedure defined in RFC5441
can be used, instead to solve your problem.
The design team will proceed with the simple designs first to push forward the
deployment, but will document the proceeding.
Cheers,
Richard
On Mon, Sep 12, 2022 at 10:50 PM Y. Richard Yang
<[email protected]<mailto:[email protected]>> wrote:
Hi all,
During the weekly meeting last week, we went over the details when deploying
ALTO in a multi-domain setting, say the FTS/Rucio setting supporting the TCN
deployment [1]. Below is the endpoint cost service (ECS) case, and it was
suggested that we post it to the WG mailing list to update the WG and get
potential feedback.
Problem: An ALTO client queries the endpoint cost from srcIP to dstIP for a
given performance metric (e.g., latency). Consider the case that the srcIP and
dstIP belong to different networks, with the whole layer-3 path as the list
[ip[0], ip[1], ..., ip[N]], where ip[0] = srcIP and ip[N] = dstIP. Define
Net(ip) as the function that maps an IP address to the network that owns the
IP---ignore the complexity such as anycast since the deployment does not have
this case. Then Net(srcIP) != Net(dstIP), if it is multi-domain. Consider the
initial deployment that we have only an ALTO server for each network; that is,
it provides ALTO service for only Net(srcIP) == Net(dstIP). Then, there is not
a single ALTO server that can provide the answer.
Basic solution (one src-dst flow): Map the list [ip[0], ..., ip[N]] to a list
of segments, where each segment starts with an IP address, and ends with the
first IP address in the sequence that leaves the network of the start IP
address. Hence, the basic query framework at an aggreation ALTO client:
- alto-ecs(srcIP, dstIP, metric)
metrics = EMPTY
ingressIP = srcIP
do {
alto-server = server-discovery(ingressIP)
(metricVal, egressIP) = alto-server.query(ingressIP, srcIP, dstIP, metric)
metrics.add(metricVal)
ingressIP = egressIP
} while (egressIP != dstIP)
The preceding assumes a procedure that collects segment attributes, and it can
be a single pass composition using a metric-dependent function (e.g., latency
is addition, and bw is min).
Multi-flow queries: ALTO ECS supports the querying of multiple src-dst pairs. A
simple solution is to query each src-dst pair one-by-one. Such a query is
necessary because the routing can be dependent on packet attributes (srcIP,
dstIP) and a pseudo packet attribute (ingressIP), and the ALTO client cannot
reuse the results. To allow reuse (both in multi-flow queries and caching of
past queries), it helps that the ALTO server indicates equivalent classes,
which Kai and Jensen investigated.
A revision of the protocol using caching and equivalent class is:
alto-server-cache: indexed by ALTO server, <attribute, mask> pairs
- alto-ecs(srcIP, dstIP, metric)
metrics = EMPTY
ingressIP = srcIP
do {
alto-server = server-discovery(ingressIP)
if (alto-server-cache.match(alto-server, ingressIP, srcIP, dstIP)
use cache results
else
(metricVal, egressIP; ingressIPMask, srcIPMask, dstIPMask)
= alto-server.query(ingressIP, srcIP, dstIP, metric)
alto-server-cache.add(alto-server, <ingressIP, ingressIPMask>,
<srcIP, srcIPMask>, <dstIP, dstIPMask>
metrics.add(metricVal)
ingressIP = egressIP
} while (egressIP != dstIP)
The mask design is a special case. For the general case, the most flexible
equivalent class may be using predicates (e.g., supporting identifying the
lower entries of longest prefix matching). It is an issue that can benefit from
more benchmarking, or if there are any related pointers, the team will
appreciate the pointers.
In the next email, Kai and Jensen will post a slightly different design
supporting a map oriented service.
Cheers,
[1] Transport control networking: optimizing efficiency and control of data
transport for data-intensive networks,
https://dl.acm.org/doi/abs/10.1145/3538401.3548550
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