If you have been enjoying your superfast fibre broadband service and finding that your VoIP or VPN functionality has been causing issues recently, there may be an explanation for this.
Adrian Kennard of Andrews & Arnold has identified a troublesome bug with the Huawei FTTC modems supplied by Openreach. If the PPPoE session restarts, then a UDP packet cache may not be cleared, and when a service such as a VPN or VoIP handset reconnects the caching means that the packets are not actually forwarded beyond the FTTC modem. This can be a very difficult problem to troubleshoot for many users and may even have caught out some of our staff recently.
"We identified the problem in some detail at the start of November having received reports from several customers in the previous months.
Our engineers worked with BT and Huawei engineers to demonstrate the exact problem and allow Huawei engineers to pinpoint the issue to a feature in the chipset in the FTTC modems. AAISP have always worked very closely with BT to resolve tricky network issues, often to the benefit of all ISPs using BT back-haul.
BT have told us that they are testing a fix for this now, but in the mean time they are happy to replace modems with a different brand for customers that are having problems."Adrian Kennard, Director, Andrews & Arnold
The problem only affects those with a static IP address, or a sticky IP (where the same IP is assigned across different authentication sessions) and the simple solution is to disconnect the Ethernet cable between the white FTTC modem (with the Openreach logo) and your Ethernet router, which will force the cache to clear. Simply rebooting your router might not be sufficient.
A bug like this can cause havoc particularly where a VPN is used to tunnel traffic between remote offices, or extensive use of VoIP is used as the bug appears to break SIP registration. Fortunately Adrian has been able to demonstrate the bug to Huawei a couple of months ago and it is now a case of waiting for a fix to be rolled out. An important point to note is that this is not specific to the Andrews & Arnold network and has been demonstrated on other networks including the BT Retail Infinity product.
We contacted Openreach to find out if there was a timeline for firmware update to the modems and were advised Openreach are waiting for confirmation of timescales on the bug fix, but expect to be able to inform communication providers of the date at the February NGA Working Group meeting. A subsequent update was received which we have copied in full below:
"Openreach completed the roll-out of updated firmware to existing end customers for Openreach's FTTC products before Christmas. As a result a small number of end customers using Huawei modems may have been impacted by a bug in the firmware release. Should the few affected end customers require a rapid fix to the problem they should contact their ISP who in turn should speak to Openreach.
Openreach will provide a further update to industry on this issue no later than the next NGA Working Group on 12 February, 2014."Openreach statement on firmware bug affecting Huawei FTTC modems
In the mean time, a mixture of training remote staff what to do if their VoIP service or VPN breaks, or deploying an alternative hardware solution can address the immediate issue. Finally, to might be possible to switch to an ECI VDSL2 modem (as opposed to Huawei) which Openreach already use. We understand previously Openreach tried to match the modem make to the cabinet hardware but believe this is no longer rigidly enforced.