[eix-wg] IXP Switching Wishlist v3.0 draft

[Fearghas McKay <]

Comments to Mike at mike@localhost


------------ Forwarded Message ------------
Date: 04 May 2005 11:42 +0100
From: Mike Hughes mike@localhost
Subject: IXP Switching Wishlist v3.0 draft

Hi all,

Here is a current draft of the wishlist, containing all recent feedback and
requests.

Key changes:

* Removed sections on MAC-SPF and MPLS options - these don't seem to be
gaining any traction, and don't seem as relevant anymore given the
improvement in things such as RSTP.

* Added section on VLAN tag space issues - tag rewrite or "virtual bridges"

* Added items on 240V AC power, and Environmental monitoring

* Added further detail to filtering, mac locking, multicast, and security.

Let me know if you have any further comments, otherwise, hope to see you
tomorrow between 11.00 and 12.30.

Thanks,
Mike
-- 
Mike Hughes     Chief Technical Officer  London Internet Exchange
mike@localhost   http://www.linx.net/
     "Only one thing in life is certain: init is Process #1"

---------- End Forwarded Message ----------



-- 
Mike Hughes     Chief Technical Officer  London Internet Exchange
mike@localhost   http://www.linx.net/
     "Only one thing in life is certain: init is Process #1"

Date: Wed, 04 May 2005 11:42:03 +0100
From: Mike Hughes mike@localhost
Subject: IXP Switching Wishlist v3.0 draft
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X-NCC-RegID: uk.linx
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Hi all,

Here is a current draft of the wishlist, containing all recent feedback and
requests.

Key changes:

* Removed sections on MAC-SPF and MPLS options - these don't seem to be
gaining any traction, and don't seem as relevant anymore given the
improvement in things such as RSTP.

* Added section on VLAN tag space issues - tag rewrite or "virtual bridges"

* Added items on 240V AC power, and Environmental monitoring

* Added further detail to filtering, mac locking, multicast, and security.

Let me know if you have any further comments, otherwise, hope to see you
tomorrow between 11.00 and 12.30.

Thanks,
Mike
-- 
Mike Hughes     Chief Technical Officer  London Internet Exchange
mike@localhost   http://www.linx.net/
     "Only one thing in life is certain: init is Process #1"
RIPE European Internet Exchange (EIX) Working Group

Internet Exchange Point Switching "Wishlist"
Version 3.0 DRAFT

Edited by Mike Hughes mike@localhost
London Internet Exchange
May 2005

ABSTRACT:
---------
At the RIPE meeting held in Amsterdam in February 2000, a number of
participants agreed that the group should produce a "wishlist" to guide
equipment manufacturers when producing boxes aimed at the core switching
market. Over the coming months, ideas were collected from the EIXP
community to form the basis of this document.

In Europe, most Internet Exchange Points use a shared switch fabric to
which the participants connect. Organisations then arrange peering via
bi-lateral peering agreements. It is not compulsory for all particpants to
peer with every other participant (called multi-lateral peering).

Once two participants agree to peer, they will set up BGP4 sessions
between their routers connected to the Exhcange to exchange routes and
traffic. In the majority of cases, the Exchange Point operator does not
become involved in the routing of any traffic across the Exchange, they
choose to leave this to the participants.

For this reason, switched Ethernet has become one of the most common
choices for Exchange Point media. The main reasons behind this are:
	* Cost effectiveness
	* Simplicity of setup
	* Can use standard CAT5 wiring - easy to implement and maintain
	* Interfaces available across a wide range of platforms

With the growth of the Internet, more and more traffic is being routed to
Internet Exchange points, and the importance of IXPs has grown in line with
this, especially in Europe where private peering is less common than North
America.

The IXP operators feel that having the right tools and features
implemented in the equipment they deploy will play an important part of
scaling ethernet technology to meet the demands placed upon Exchange Points.

This is an informational document to outline the various features which
IXPs would like to see implemented in core Ethernet Switching products.


SECURITY AND MANAGEMENT FEATURES:
---------------------------------

a) Control of dynamic MAC learning
----------------------------------
Currently, switches are provided with two options, either statically
configured or dynamically learned forwarding information.

Exchange Points like to monitor and control how many MAC addresses are
connected to a participant's port. The XP operator generally does not
desire ad-hoc extensions connected to their network. The common way of
managing this is to enforce a "router-only" or "limited MAC address" rule.

This is currently controlled by statically configuring forwarding
information, or not controlled, but policed by counting the number of
MAC addresses learned on each port, and action taken against offenders.

Static configuration of forwarding information is a somewhat inelegant
option, as this increases configuration overhead, and decreases
flexibility, especially in case of emergencies.

We propose a configurable "maximum learning" limit, configurable on a
per port basis. In this way, operators can configure participants ports
according to their house rules, but retain the flexibility of dynamic
learning.

The filtering should not impose a performance hit on those ports which are
mac-limited.

The lockdown should automatically flush when there is a state transition on
the interface.

There should be multiple levels of locking:

* "Forwarding" limit - the maximum number of addresses you will forward for
on this port
* "Soft" limit - the limit at which you will record syslog events
* "Hard" limit - the limit at which you shut down the port (drop link if
able) and record a syslog event

A hard limit should require manual intervention to reset the locking and
bring the port back up.

This feature must include a "first in-last out" mechanism in the lockdown
facility, to avoid forwarding information for valid addresses being
overwritten by addresses in excess of the exchange's house rules.

All the above locking, timeout, and reset rules should be configurable by the
network operator.

b) Disable acting on STP BPDU information
-----------------------------------------
Many exchange operators currently deploy Spanning Tree Protocol (STP) in
networks which contain redundant links/full meshing.

There is however, a danger presented by STP information leaked from a
participant's network. The participant may have connected a poorly
configured switch/router product, and may be leaking their STP
information into that of the exchange.

We would wish to see a configurable option to allow STP information to be
ignored, and filtered in hardware on "edge ports", on a per port basis.

There should also be an option to generate traps or log messages based on
transgressions of the policy.

c) Wire-speed ACL-type filtering based on L2/L3 header info
-----------------------------------------------------------
The ability to look into the layer 2 or 3 header information of a packet,
and selectively monitor, or filter, based on certain layer 2 or 3 criteria.
This could be done using pattern matching or masking.

A common example of an area where this is desirable is to permit frames of
only certain ethertypes to enter the network through an edge port.

This sort of filtering should be implemented in hardware wherever possible,
and not have an effect on the forwarding performance of the system. Where
this is not possible, it must be clearly documented.

d) ARP/Broadcast snooping and control
-------------------------------------
Many exchange points insist on participants using IP addresses they have
assigned by the exchange operator. It is desirable for the operator to be
able to monitor/restrict "off-net" ARP.

As Ethernet is a broadcast medium, broadcast storms have been known to
bring exchanges to their knees, affecting the forwarding abilities of both
the exchange's switches, and the participants' routers.
Monitoring/rate limiting/control of Ethernet broadcast frames is
desirable.

Most exchanges also forbid the speaking of interior routing protocols
across their peering network. Since these take the form of broadcast or
multicast frames on ethernet, control would help monitor this type of
incidence.

Such control should be able to distinguish (through appropriate
configuration) between legitimate ARP and genuine broadcast storms.

There should be suitable configuration knobs to be able to rate limit, shut
down, log exceptions, etc.

e) Support for MARP?
--------------------
We had looked at seeking support for something such as MARP - "MultiAccess
Reachability Protocol". This was defined in an Internet Draft, which allows
for detection of failures at L2 across multiple switch hops.

However, this has failed to become published as an RFC, as Cisco has
asserted IPR over the content of the draft, and would therefore require
licencing. This seems to have somewhat killed this promising idea off.

f) Policy exception logging
---------------------------
In the above paragraphs, we have asked for some policy-based tools.
Operators need to know when these policies have been breached.

Good logging of policy exceptions need to be implemented:
	* SNMP-trap
	* Configurable syslog (i.e. which syslog facility to write to)
	* RFC3164 compliant syslogging
	* Syslog over SSL

g) Access to management interfaces
----------------------------------
In the past, security of management interfaces on Ethernet switching
products as often been lacking.

CLI or web interfaces should support authentication using
username/password pairs, to avoid the use of "password only"
authentication which implies shared passwords.

CLI interfaces should also support SSHv2 access, using either
username/password pair, or public key authentication.

Web interfaces should be HTTPS/SSL enabled, to avoid passwords being
passed in the clear over HTTP.

Support SCP/SFTP for config copy/upload/download, as well as existing
methods (TFTP/FTP).

Management interfaces should be able to perform authentication from an
external source, such as TACACS, RADIUS or LDAP services, as well as
providing locally held accounts (have to be retained for emergencies)

All management interfaces, CLI, web and SNMP should be able to benefit from
access-list control. The access lists should be able to support
variable-length subnet masks.

Ability to disable management interfaces on a per-VLAN basis. Many XP
operators choose to configure a "management" VLAN, so that all
management is done out-of-band of the core peering traffic. It is
desirable to have the management interfaces to listen on the management
networks only.

On devices which are designed to support high bandwidth per-slot, such as
high-density GigE or 10GigE, it is preferable to have a 10/100 Mb
management port provided on the system, to avoid burning a fast port for
management.

h) Port mirroring
-----------------
It is sometimes necessary to mirror participants' ports, either because a
participant is suspected of some inappropriate activity, or to help obtain
information to debug a problem.

Not all exchange points have staff on site 24x7, and port mirroring may
need to be remotely set up, without hands-on intervention on-site.

The ability to allow any port to mirror any other port with a similar
lower speed within the chassis would allow the operator to connect a
traffic collector/analyser device to a monitoring port, and simply
configure the switch to mirror a port as desired to monitoring port.

i) Statistics and Accounting
----------------------------
As well as implementing defacto SNMP counters/RMON, also consider
implementing the following:

* Per-VLAN traffic statistics
* sFlow export support (via management interface)
* Counters based on common ethertypes (IPv4, IPv6, multicast, ARP, etc)


SCALABILITY AND RESILIENCE
--------------------------

a) Spanning Tree
----------------
Spanning Tree is currently the only cross-platform dynamic solution
available to operators of exchange points for dynamically managing multiple
redundant links in their architecture.

There are a number of problems with Spanning Tree:
	* Slow convergence
		- especially in cases of root bridge re-election
	* Wasteful of reslilent/redundnant resources
		- redundnant links are switched off
		- no traffic sharing
	* Security concerns (highlighted above)

As the routes collected at an Exchange Point can be routed all over the
world, any routing instability can act like dropping a pebble in a pond,
and will spread around the Internet.

It's desirable to maintain stable routing sessions across Exchange Point
LANs to minimise these routing flaps, because of load it places on routers,
and the effects of route dampening penalties.

We believe that being able to declare ports as "end-stations" should
avoid them being counted in the STP calculation, enable these ports to
start forwarding more rapidly, and speed overall STP convergence time.

Rapid spanning tree (IEEE 802.1w) should be implemented
(http://www.ieee802.org/1/pages/802.1w.html), and results from testing RSTP
on certain platforms show that for simple topologies with few redundant
links, sub-second failover and reconvegence is achievable with minimal
tuning or additional configuration.

b) Ring Restoration Protocols
-----------------------------
IEEE 802.17 - This is a standards-based version of the technology currently
used by Cisco called DPT (Dynamic Packet Transport). This consists of a
counter-rotating ring-system, with spacial reuse and "ring wrapping"
circuit protection.

The Cisco version is currently implemented over SONET/SDH media,
however, the standardised version is being designed to be more media
agnostic, and the IEEE working group has already elected to provide
support for Gigabit Ethernet and 10 Gigabit Ethernet.

Proprietary Protocols - There are a number of proprietary ring protocols,
such as Extreme's EAPS (published as informational RFC3619), or Foundry's
MRP.

They are relatively similar in operation, in that they make assumptions
about the number of redundant links in a topology (i.e. only one), have a
concept of master and transit nodes, use a "heartbeat" sent out by the
master, and topology change messages are passed between the nodes to speed
network reconvergence (by triggering FDB flushing, and backup port
unblocking on the master node).

These recovery protocols may become less important as RSTP becomes more
graceful.

c) Trunking and Link-Aggregation
--------------------------------
It's become increasingly common for exchange points to become multiple
switch and multiple site based, and many need to deploy link aggregation to
handle the volume of interswitch traffic, where it exceeds the maximum
speed of a single link.

Most equipment implements load-sharing using either round-robin or
address-based algorithms.

In exchange points, many pieces of equipment will have similar MAC
addresses, especially the first and last bytes (corresponding to vendor and
slot position on router).

This causes significant problems if the load-sharing hash does not use
enough significant bits in the frame. If the hash is only based on part of
the address, this can result in poor efficiency of load-sharing, and
"clutching" of traffic on a single link inside a group.

It's prefereable that load-sharing algorithms should consider the whole L2
address, and where possible the L3 header information, when calculating the
hash used.

Load-sharing of broadcasts and multicast traffic should be implemented.
This is because behaviour such as forwarding all broadcast/multicast
traffic out of the "primary" port in a trunk have been observed when
load-sharing using destination MAC addresses has been implemented.

IEEE 803.3ad link-aggregation "LACP" should be implemented.

d) Multicast Control and Containment
------------------------------------
Most switches are configured with IGMP snooping for multicast control.

However, in an exchange point, with only routers attched, there is no
IGMP present, only PIM and MSDP, and all multicast packets are flooded out
of all ports.

An exchange point, however, is an ideal place for mutlicast peering to
happen, inject the traffic once, and it comes out several times (as much as
is needed, or in the current situation, as much as isn't needed!).

Cisco developed RGMP (Router Group Management Protocol). This is a
proprietary technology whereby the router can communicate to the switch
which multicast groups it wishes to see.

This remains, despite being released as an informational RFC (RFC3488), a
vendor specific feature, and a wide range of routing and platforms are
present at many exchange points - both in equipment used by the operator,
and the participants. These are true multi-vendor environments.

Therefore, this is not a workable solution for most exchange points,
whose princples are often include "equal treatment" of participants.

While it may not solve all potential issues with multicast peering,
implementing PIM-SM snooping and pruning within the switches will
achieve the traffic containment requirements.

Where PIM snooping is available, this should not have a negative effect on
the overall forwarding perfomance of the system. Where there is a
performance impact, this and it's surrounding caveats shall be clearly
documented.

e) VLAN tagspace issues/overlapping
-----------------------------------
A serious emerging issue is VLAN tag space overlapping/clashing issues.
Most metro transport networks can solve this by using q-in-q (tag
stacking), however, this doesn't apply to shared networks like Internet
Exchanges.

Current switches use a 1:1 mapping of 802.1q vlans to bridge groups,
which is the way 802.1q was probably intended. This mapping should be
loosened if not abandoned - nowadays there are so many ways to egress an
ethernet frame from a switch that more and more often we have
to resort to 'tricks' to put the right label on the right ethernet
packet going out the right interface.

This problem is being exacerbated by a number of issues:

* Increased use of switch router products (e.g. Cisco 7600)
* Use of switches as "channel-banks" - breaking out higher speed router
interfaces
* Use of metro-ethernet, lan extension or Ethernet over MPLS ("Martini")
circuits to connect to the IXP

We think there are two (fairly similar) approaches to solving this:

* Basic VLAN tag rewrite
* Separate the tag from the virtual bridge instance

VLAN tag rewrite is, as it's name suggests, being able to rewrite a dot1q
tag on a specific interface to a VLAN ID on the switch. This would need to
be implemented on both ingress and egress.

The other option is complete seperation of VLAN ID from the virtual bridges
inside the switch. You assemble a framework where you can place untagged
ports, tagged ports, q-in-q tagged ports, mpls endpoints, atm vc's all
together in into the same virtual bridge. Effectively a bridge group which
can contain any number of these sort of entities.

f) Link failure detection
-------------------------
Link failure detection should be implemented, and should look like:

* UDLD - Uni-Directional Link Detection
* LFN - Link Failure Notification

This avoids the risk of an ethernet link going "one-way" and fooling the
restoration protcols that the link is working, when really it isn't.

ENVIRONMENTAL MONITORING
------------------------

There should be reasonable environmental monitoring provided:

* Temperature sensors
* Fan health sensors
* Power supply health sensors

There should be exception logging via SNMP trap and syslog (as specified
above) of any incidents.

It should also be possible to shut down a malfunctioning element in the
system (automatic, user configurable, or manual), in order to preserve
system health.

For example, a power supply failing in a system could cause an instability
in the device. If the system could make a decision to shut that power
supply down, and assuming a redundant configuration, the switch would then
operate in a stable condition until such time that the power supply could
be exchanged.

PHYSICAL WISHES
---------------
IXPs are high-uptime environments. The equipment used in an IXP needs to be
able to satify this requirement, in terms of redundancy, and hot-swappable
components.

* Hot swap of management/switch fabric cards with instantaneous failover to
any installed redundancy (not rebooting onto the "backup")
* Full-redunancy of PSUs, and hot-swap (i.e. box should run on 50% of
PSUs)
* Rapid booting and card startup (after all, much functionality is
implemented in the ASIC hardware)
* GBIC/SFP-optics for flexibility, easy replacement, and maximised port
utilisation (freedom to choose SX/LX, etc)
* "Coloured" (DWDM/CWDM) GBIC/SFP/Xenpak/XFP (etc, etc) support
* Vendor "lockdown" of pluggable interfaces should either not be
implemented, or be able to be switched off in configuration.
* 220-240V AC power options. Unlike most telco-managed facilities, the
carrier-neutral facilities common in Europe do not provide indigenous 48V
DC power. Power distribution is done using the regular utility supply
voltage in that country - usually ~230V AC in EU countries.
* Cable testing functionality in copper ports, and optical power metering
in optical ports.

ACKNOWLEDGEMENT AND THANKS
--------------------------
Thanks are due to the "usual suspects" in the RIPE EIX Working Group, but
specifically Christian Panigl, Kurtis Lindqvist, Keith Mitchell, Daniele
Arena, and Remco Van Mook, for their contributions to this document.