Greetings,
Given the importance of Citylink's IX services in the community, I feel
that it is valuable to notify this communication from them to the entire
list.
I would note that they are explicitly stating in this communication they
will not ever forcibly require consistent behavior. I would note that this
is in direct violation of RFC7947;
*2.2.2.1. Route Server AS_PATH Management*
* As a route server does not participate in the process of forwarding*
* data between client routers, and because modification of the AS_PATH*
* attribute could affect the route server client BGP Decision Process,*
* the route server SHOULD NOT prepend its own AS number to the AS_PATH*
* segment nor modify the AS_PATH segment in any other way.*
I would like to encourage (publicly) that Citylink implement this
consistently, rather than in a haphazard way that varies customer by
customer. Consistency is the key to supporting the NZ internet
effectively *(Note,
RFC7947 doesn't say "do this when your customer can be bothered")*.
Additionally, I would like to encourage Citylink to communicate with the
NZNOG community when publishing updates that could have an operational
impact on the internet in NZ as a whole.
Cheers,
Tim
####### FOREWARDED MESSAGE BELOW #######
Dear REDACTED
CityLink would like to inform you of some exciting NZIX developments that
concern your existing ExchangeNET connection(s). We’re introducing some
changes to the way we operate the NZIX route servers in order to improve
our compliance with recent proposed standards (RFC7947 and RFC7948), and to
minimise the disruption caused by routine administrative changes going
forward.
*Background*
CityLink provides two route servers at each of the NZIX exchanges
- currently Auckland (APE), Hamilton (HIX), Wellington (WIX), Christchurch
(CHIX) and Dunedin (DPE). The route servers facilitate
multilateral interconnection between the participants at each exchange by
simplifying the BGP configuration and admin overhead otherwise needed
to exchange routing information between multiple eBGP speakers. The NZIX
route servers have traditionally prepended the exchange’s Autonomous System
(AS) number to the AS path of the prefixes they advertise back out to peers.
*What is changing?*
A number of ExchangeNET customers have expressed a preference that the NZIX
route servers no longer prepend the exchange AS number to the AS path of
advertisements sent to them. This preference is consistent with recent
proposed standards (RFC7947 and RFC7948), and is the recommended best
current practice for Internet exchange route server operation. However, in
order to put this change into effect, ExchangeNET customers who peer with
the NZIX route servers may need to make a (potentially disruptive) change
to their existing BGP configuration.
While CityLink would prefer all ExchangeNET customers peering with the NZIX
route servers to support this alignment with best current practice, we
recognise that the timing to implement such changes may differ based on
your individual business needs. Therefore, we have decided to implement the
changes on a per-participant basis, and we invite those
ExchangeNET customers who would like to “opt-in” to the changes (that is,
for the NZIX route servers to no longer prepend the exchange AS number to
the AS path of the advertisements sent to them), to contact us. We will
endeavor to accommodate requests for configuration changes to be made at
times convenient for each ExchangeNET customer, commencing from *13th March
2017* onwards.
*Note:* We will *not* be changing the configuration of any existing
sessions without that participant’s agreement.
*What are the implications of the change?*
· ExchangeNET customers who peer with the NZIX route servers will
see the AS path for prefixes received shortened by one hop (the exchange AS
number). This may alter the current choice of best path for those prefixes.
· If you had been using the presence of an exchange AS in the AS
path to influence your organisation’s routing policy, you may need to amend
your configuration in order to achieve your routing policy objectives. It
may not be quite so obvious that a given route has been learnt from a
particular NZIX exchange point going forward.
· Your router may need to be configured with its equivalent of *no
bgp enforce-first-as* to restore its BGP session(s) with the NZIX route
servers after the change is made.
*I’d like to “opt-in” to the change. What do I need to do?*
If you’d like us to remove the exchange AS number from the AS path of the
advertisements you receive from the NZIX route servers, please email
us at *peering(a)citylink.co.nz
