Work to help resolve recent LNS problems (Updated 9th Feb)
MAINTENANCE Open Broadband
STATUS
Open
CREATED
Jan 19, 03:55 PM (1½ months ago)
AFFECTING
Broadband
STARTED
Jan 19, 03:50 PM (1½ months ago)
REFERENCE
42608 / AA42608
MASTODON
INFORMATION
  • INITIAL
    1½ months ago by Andrew

    This is a summary and update regarding the problems we've been having with our network, causing line drops for some customers, interrupting their Internet connections for a few minutes at a time. It carries on from the earlier, now out of date, post: https://aastatus.net/42577

    We are not only an Internet Service Provider.

    We also design and build our own routers under the FireBrick brand. This equipment is what we predominantly use in our own network to provide Internet services to customers. These routers are installed between our wholesale carriers (e.g. BT, CityFibre and TalkTalk) and the A&A core IP network. The type of router is called an "LNS", which stands for L2TP Network Server.

    FireBricks are also deployed elsewhere in the core; providing our L2TP and Ethernet services, as well as facing the rest of the Internet as BGP routers to multiple Transit feeds, Internet Exchanges and CDNs.

    Throughout the entire existence of A&A as an ISP, we have been running various models of FireBrick in our network.

    Our newest model is the FB9000. We have been running a mix of prototype, pre-production and production variants of the FB9000 within our network since early 2022.

    As can sometimes happen with a new product, at a certain point we started to experience some strange behaviour; essentially the hardware would lock-up and "watchdog" (and reboot) unpredictably.

    Compared to a software 'crash' a hardware lock-up is very hard to diagnose, as little information is obtainable when this happens. If the FireBrick software ever crashes, a 'core dump' is posted with specific information about where the software problem happened. This makes it a lot easier to find and fix.

    After intensive work by our developers, the cause was identified as (unexpectedly) something to do with the NVMe socket on the motherboard. At design time, we had included an NVME socket connected to the PCIE pins on the CPU, for undecided possible future uses. We did not populate the NVMe socket, though. The hanging issue completely cleared up once an NVMe was installed even though it was not used for anything at all.

    As a second approach, the software was then modified to force the PCIe to be switched off such that we would not need to install NVMes in all the units.

    This certainly did solve the problem in our test rig (which is multiple FB9000s, PCs to generate traffic, switches etc). For several weeks FireBricks which had formerly been hanging often in "artificially worsened" test conditions, literally stopped hanging altogether, becoming extremely stable.

    So, we thought the problem was resolved. And, indeed, in our test rig we still have not seen a hang. Not even once, across multiple FB9000s.

    However...

    We did then start seeing hangs in our Live prototype units in production (causing dropouts to our broadband customers).

    At the same time, the FB9000s we have elsewhere in our network, not running as LNS routers, are stable.

    We are still working on pinpointing the cause of this, which we think is highly likely to be related to the original (now, solved) problem.

    Further work...

    Over the next 1-2 weeks we will be installing several extra FB9000 LNS routers. We are installing these with additional low-level monitoring capabilities in the form of JTAG connections from the main PCB so that in the event of a hardware lock-up we can directly gather more information.

    The enlarged pool of LNSs will also reduce the number of customers affected if there is a lock-up of one LNS.

    We obviously do apologise for the blips customers have been seeing. We do take this very seriously, and are not happy when customers are inconvenienced.

    We can imagine some customers might also be wondering why we bother to make our own routers, and not just do what almost all other ISPs do, and simply buy them from a major manufacturer. This is a fair question. At times like this, it is a question we ask ourselves!

    Ultimately, we do still firmly believe the benefits of having the FireBrick technology under our complete control outweigh the disadvantages. CQM graphs are still almost unique to us, and these would simply not be possible without FireBrick. There have also been numerous individual cases where our direct control over the firmware has enabled us to implement individual improvements and changes that have benefitted one or many customers.

    Many times over the years we have been able to diagnose problems with our carrier partners, which they themselves could not see or investigate. This level of monitoring is facilitated by having FireBricks.

    But in order to have finished FireBricks, we have to develop them. And development involves testing, and testing can sometimes reveal problems, which then affect customers.

    We do not feel we were irrationally premature in introducing prototype FireBricks into our network, having had them under test not routing live customer traffic for an appropriate period beforehand.

    But some problems can only reveal themselves once a "real world" level and nature of traffic is being passed. This is unavoidable, and whilst we do try hard to minimise disruption, we still feel the long term benefits of having FireBricks more-than offset the short term problems in late stage of development. We hope our detailed view on this is informative, and even persuasive.

  • UPDATE
    28¼ days ago by Andrew

    5th Feb: Both Z and Y have hung in recent days (Saturday 3rd and Monday 5th) - we are currently analysing the data from the various cache and memory systems that we were able to retrieve from the hardware whilst it was in its hung state.

  • UPDATE
    24½ days ago by Andrew

    Latest Summary, as of 9th February: We now have a larger pool of FB9000 LNSs. Six out of seven of them have been fitted with NMVe drives and JTAG debugging capabilities. If/when they have a hardware lock-up we'll be able to gain a bit more of an insight in to the cause. The seventh LNS has not, but it has been stable with an uptime of 86 days.

  • UPDATE
    4 days ago by Andrew

    Work being carried out:

  • NEXT UPDATE...

    Due 15¾ hours ago (overdue)