Summary of pre-GDB on IPv6, June 11, 2014 (CERN)


IPv6 1010 - E. Martelli

See slides, in particular for address formats.

No more broadcast addresses: replaced by special multicast addresses

Fragmentation/reassembly no longer permitted in routers: have to be done at source and destination.

ARP replaced by NDP (Network Discovery Protocol)

  • Based on 5 types of ICMP packers: RS/RA, NS/NA, Redirect

SLAAC : address autoconfiguration

  • Require a routed IPv6 network
  • Based on ICMPv6 RD/RA packets + EUI-64 for generating local part of the address (derived from MAC address)

Several routing protocols

  • IPv4 ones have a new version for IPv6 only
  • ISIS : IPv4 and IPv6
  • BGP : IPv4 and IPv6

Selecting IPv4 vs. IPv6

  • Client decision based on DNS reply
  • Generally one tried first (based on app config) and the other one tried if the first one is not replying: users will experience a delay (30 to 180s) if they have to way for the timeout
  • Some apps (e.g. some browsers) start to try both at the same time and use the one which answers first to avoid this problem

IPv6 - IPv4 Semantics Differences - F. Prelz

Every network endpoint is ALWAYS associated to multiple active network address: at least a ''link-local'' and one or more global addresses

  • Origin and destination addresses have to be choosen for each connection: done with new system configuration parameters
    • `/etc/gai.conf` and `ip -6 addrelabel`)
    • Except for Mobile IP extension that defines the concept of a ''Home Address''
  • Deciding between IPv4 and IPv6 first is just a special case...
  • Main RFC related to this issue: RFC6724
  • Consistencies issues seen when upgrading from SL5 to SL6
  • This difference is probably the main challenges in making apps IPv6-ready: most apps are not prepared to deal with a potentially large set of addresses

IP route assignment: only possible via a static route definition or via ''Router Advertisements'' which are multicast messages

  • Default route cannot be assigned by dhcpv6

IP address and DNS server assignment

  • DNS automatic update through Router Advertisements in stateless configuration should allow painless DNS configuration... but the RFC is not supported by some major vendors (e.g. CISCO)

Security potential implications

  • Handling of header extensions optional in IPv4 are required in IPv6: good portion of new codes that may be a good target for vulnerability attacks
  • Large number of optional protocol headers may mean that the upper-layer payload useful for filtering/firewalls may not be in the first fragment, requiring packet reassembly
  • ICMPv6 is now required, at least on a network segment

IPv6 Deployment at CERN - E. Martelli

Dual stack done

  • Network DB: IPv6 is now the main navigation data, IPv6 address tables fully populated
  • Same routing infrastructure: BGP + OSPF

Identical perfs for IPv4 and IPv6

  • All production network can forward IPv6 packets at wire speed
  • Only exception: policy based routing for stateful firewall bypass but not a showstopper currently as IPv6 traffic is low

Common provisionning tools for IPv4 and IPv6: no change for users and network admins

  • IPv6 info fully exposed
  • Users can define their devices as IPv6-ready (connectivy ok, apps listening on both IPv4 and IPv6 addresses)

Same network services: dns, dhcp, firewall...

  • firewall: most ACLs translated automatically for IPv6, a few additional rules IPv6-only


  • Size of routing tables and ACLs have doubled
  • dhcpv6 still in an early stage
    • RAs necessary to configure default gateway and prefix length but no predictive load balancing in multi-router subnets: all prefixes exposed
    • MAC address authentication not always work with IPv6: no requirement to use the MAC address of the interface the packet is sent throug. Management of UUID is required.
  • New security threat to take into account
  • New issues to be solved by support lines

Lessons learnt

  • dhcpv6 is definitely not dhcpv4
  • Do a staged deployment, involve users of different profiles


GridFTP Tests - T. Wildish

3.4 PB transferred since the beginning of test 1 year ago

  • Not a heavy traffic
  • Everybody can play: only need an IPv6-enabled gridftp and an IPv4 uberftp
    • 20 GB of disk required
  • Best effort support

gridftp dashboard useful to identify problems

  • see slides

Future plan: moved to a FTS3-based testbed

  • Currently PHEDEX-based

IPv6 Readiness and Configuration Guidance

WLCG SW and Tool Survey - D. Kelsey

  • Good progress in coverage but still several important apps not covered (e.g. ARC CE and CREAM CE)

About to start looking at storage and batch systems

DPM - S. Skipsey

DPM itself is IPv6-compliant out of the box some dependencies requiring specific steps/versions

  • Globus libs need changes to standard `/etc/gai.conf` to bind to IPv6
  • MySQL v5.5+ required
    • Can use localhost alternatively
  • YAIM needs hacks as it relies on IPv4 behaviour
  • BDII must be dual-stacked for using IPv6 DPM
  • fetch-crl sometimes have problems if binding to IPv6

DPM protocols

  • gridftp: dependant on Globus libs, third-party gridftp needs some standard agreeements
  • xrootd v4 is IPv6-compliant but not xrootd v3 API compatible: new DPM plugin currently being tested
  • http: no known issue

dCache - U. Tigerstedt

Ipv6 support ready since 2.9 but not enabled by default

gsiftp: changed in 2.9.4+ to comply with globus-url-copy and DPM gsiftp rather than the standard...

xrootd: since 2.9.4+, IPv6 ready, compatible with xrood v4 client

StoRM - C. Walker

Not really tested by developers but supposed to work.

QMUL tested it and found no issue except the incorrect log of IPv6 addresses to be fixed in GT6

  • Also MySQL requires a minimum version to use IPv6 if wanted
  • `gai.conf` needs to be updated to prefer IPv6 in a dual-stack environment
  • Backend not starting correctly on reboot: being investigated
  • Configuration adjustment needed to use IPv6 addresses instead of host nmaes in SURL

FTS3 - M. Salichos

Problems identified with some dCache endpoints but no time to troubleshoot them yet: may be related to configuration problems or dCache version before 2.9

  • Only problems in the gridftp transfer phase
  • Presently prevents enabling IPv6 in production
    • Decision should be taken by developers and experiments
  • Tests done last Friday... more investigation needed
  • Imperial College used to run a dual-stack FTS3 instance and saw no problem with any site...

Known issues in dependencies

  • ActiveMQ: IPv6-ready but the C client used by FTS3 was not until a very recent version
  • MySQL v5.5+ is required
  • GFAL2: IPv6 must be explicitly enabled in `/etc/gfal2.d/gsiftp_plugin.conf`

Xrootd - L. Janyst

xrootd v4 client is IPv6-ready: old client is deprecated

  • Will prefer IPv6 if available
  • No configuration necessary except if wanting a different default binding strategy
  • Old clients will work perfectly with xrootd v4 servers in IPv4

xrootd v4 server is also IPv6-read

  • As for the client no configuration necessary if default configuration (dual-stack) is suitable

Federation (4.1): no longer any requirement for dual-stack servers

  • Redirectory will attempt to match a downstream server with the same capacity as the client if the client is IPv4 or IPv6 only
  • If both are supported by the client, both will be tried and the less loaded (the one answering the more quiclky) will be used

Batch Systems - F. Prelz

Not a very critical issue: CE acts as a protocol translator, no direct connection to the batch system from out of the LAN

LSF: supposed to be IPv6-ready and dual-stack friendly for a very long time, v9 documents how to enable/configure it

  • Cannot mix IPv4-only and IPv6-only nodes in the same cluster
  • Not aware of any dual-stack validation in the community

Condor: single-stack pool operation available in v8 but dual-stack pools supposed to be rolled out in 8.3

  • Problem with multiple addresses per endpoint)

Grid Engine: IPv6 support in UGE claimed for 8.3 (currently 8.1)

  • A plan since 10 years...


  • A SVN ipv6 branch started in 2007 and died since then...
    • Network code spread everywhere...
  • Reports from different groups that a dual-stack Torque fails
  • No plan for PBS Professional too

SLURM: claim that adding the IPv6 support should be straightforward but no real work started

  • Impacted code seems to be concentrated in a few places...

Experiment Plans

ATLAS, CMS and LHCb - A. Dewhurst

Current VO focus is SW for Run2

  • Hopefully this SW will make IPv6 testing easier
  • Expect IPv6 support rollout to take many years...

When possible, experiments plan to make their central services dual-stack asap

  • Medium term: SE with dual-stacked protocols
    • When enough available, IPv6-only CE/SE would be feasible
  • ATLAS AMI: based on an Oracle back-end hosted at CCIN2P3, plan to dual-stack web frontends if possible

Workload Management Systems

  • PanDA: currently migrating to BigPanda, exclusively using http so should work, Pilot factory had some initial evaluations with dual-stack
    • Imperial is planning a dual-stack BigPanDA test instance
  • CMS: validation not yet started but no problem anticipated (rely on CondorG + glideinWMS that are supposed to work)
    • Dual-stack glideinWMS pilot planned soon
    • Also need to test CRAB3 used by users to submit analasys jobs
  • DIRAC: recently tested from a dual-stack client, no issue found
    • Next test: IPv6-only WN

Data management: all exps relying on gridftp, xrootd and http

  • Mainly throug FTS3
  • See previous discussion for exact plans
  • ATLAS has setup a testing infrastructure for Rucio validation (stress tests): could be reused for IPv6 tests
  • CMS already validated IPv6 xrootd: next step is to validate AAA
    • NEbraska will enable IPv6 to their xrootd servers from US redirector next week
    • CMSSW: a new release needed to upgrade the xrootd client
  • LFC: not used or about to be abandoned in the next year, no plan to test


  • Frontier/Squid still relying on Squid 2.x which is not IPv6 compliant
    • Squid 3.x is IPv6 ready but has long running problems that may impact significantly performances (lack of collapsed forwarding, now fixed and headers not updated)

CVMFS should work fine

  • Has no problem with Squild 3.x


  • A. Hanuchevsky: was there a study on the impact of IPv6, apart from enabling the stack (network infrastructure, router replacement...)
    • Dave: no. Difficult to do as it is very site dependent.

ALICE - C. Grigoras

All central services are IPv6-ready exept the API service based on Xrootd

  • All dual-stacked a while ago
  • DNS load balancing includes both IPv4 and IPv6 addresses
  • No problem found... but almost no IPv6 requests

Sites services: several known issues

  • VOBOX perl http server used by CE, Packman and CMReport
    • Need to upgrade to perl 5.14+ to get native IPv6 support: also doable with a backport to 5.10
  • Xrootd/EOS
  • ApMon
  • Need to upgrade AliEN xrootd clients to v4 and v4 API
  • 4 sites have deployed dual-stack VOBOX: more welcome

Monitoring: work to be done to integrate IPv6 network information in testing and network path calculation

Monitoring IPv6

perfSonar - D. Rand

perfSonar can run bwctl and owamp tests in IPv4 or IPv6, specified on a node by node basis.

  • -v4 or -v6 suffix added to hostname

A Mash dashboard instance setup for IPv6 tests at Imperial College

  • Asymmetry shown on several routes: to be investigated
  • Allow a comparison with IPv4 results
  • Open to new sites who had like to benefit from IPv6 testing with perfSonar

Nagios - M. Elias

Access to the service through http: ok

  • Several plugins available for basic IPv6 testing

Livestatus + check_mk multisite: multisite not IPv6-ready in current version


  • Ping: by default selects IPv4 or IPv6. Would be good to run both
  • NRPE: ok in SL6 (not in SL5)
  • NSCA: no support for IPv6
    • Hopefully a future version will support it
  • port checks: need to run both for IPv4 and IPv6
    • check_46 plugin can help

Other monitoring tools

  • munin: no problem with IPv6
  • Ganglia: bascially works but a few configuration issues

Site Status and Plans

Site Survey - D. Kelsey

Run end of May

T0 and T1s

  • Only CERN foreseeing a lack of IPv4 addresses
  • 7 T1 with partial IPv6 readiness, 4 without
    • 6 with plans for complete basic readiness in the next year


  • 5 sites aleady with IPv4 address shortage
    • Private IPv4 WNs: not used at most sites
  • 16 with full IPv6 connectivity, 9 with partial
    • 60 without IPv6 connectivity: 45 with no plans

UK IPv6 Status - C. Walker


  • All services except dCache dual stack
  • Some IPv6 only node
  • DPM and StoRM tested
  • Failed attempt with OpenStack Havanna

QMUL, Brunel, Oxford

  • perfSonar + RIPE probe
  • Brunel and Oxford: test DPM
  • QMUL: test StoRM, in production soon

Main questions are operational ones: address allocation policy, dhcpv6 vs. SLAAC, firewall (ip6tables)

  • In particular dhcpv6 doesn't configure router: how to do it? RA?

IPv6 at FZU (Prague) - M. Elias

IPv4 shortage: just one C class

  • Started to investigate IPv6 in 2011

Testbed started to test current tools and administration process

  • PXE: no IPv6 support
  • New config management tools: Puppet
  • Integrated with Nagios monitoring

Perfs: reached 21 Gb/s consolidated for DPM traffic

IPv6 at BITP (Uraina) - O. Shadura

See slides

Wrap-Up - What Next?

Next testing

  • Continue file transfer testbed with more storage options
    • Involve all t1s?
    • Invite T2s?
  • FTS3 IPv6 pilot: taken forward by FTS3 dev team, experiments and OpsCoord
  • Atlas AMI
  • IPv6-only WNs

Other issues

  • Squid v3 issues preventing its use

Monitoring: important to set up the appropriate monitoring as we are moving to production

  • perfSonar is an important piece and a good way to start for a site

Objective for next year: foster adoption of dual stack for production services at several/many sites

  • WG could help to coordinate the move to avoid every site running into the same problems at the same time
    • In fact sharing of experience worked well so far...
    • Sites should start by setting up their IPv6 basic network infrastructure

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Topic revision: r1 - 2014-07-10 - MichelJouvin
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