This page lists the problems we have found and raised regarding the ZyXEL VMG1312.

Problem List

TL;DR (Brief overview of the problems listed below)

The main problems are:

MTU 1500 is not supported on some setups (Internet access will still work fine, but we'd like 1500) - Still under evaluation with ZyXEL, may or may not happen.
VPNs may not reconnect if PPP drops - until you unplug and replug the LAN-side ethernet cable! We saw this same thing last year with Huawei HG612, which use the same chipset.

Bridging 1508 bytes ethernet

Issue Description

We need the router to support baby jumbo frames bridging to VDSL and ADSL, to support *at least* 1508 bytes to allow RFC4638 PPPoE to a connected device.

Date Reported

2015-02-19

Updates

2015-02-19 ZyXEL development team aware, and are looking in to whether they can support this feature. 
2015-03-28 Still ZyXEL HQ are still evaluating the effort to make this change.
2015-04-14 ZyXEL are working on supporting larger Ethernet frame sizes as part of the 'BT Lab modem conformity tests' (SIN 498). No ETA though.

Resolution

None yet.

IPv6 RA on LAN

Issue Description

We are seeing a slight issue with IPv6 RA on the LAN. We are getting a prefix from the PPP link on VDSL. When PPP comes up, several seconds later the router does a DHCPv6 on the WAN, and then does an RA on the LAN, which works. We are puzzled by the noticeable delay in DHCPv6 PD which delays IPv6 connectivity. If PPP drops for any reason it appears to withdraw the RA on the LAN immediately, which is fine. However, when PPP reconnects it does not re-send the DHCPv6 on the WAN. This may be deliberate, and in our case it is probably OK, but it is something of an assumption that the previous DHPCv6 remains valid on the PPP after a reconnect. I'd suggest a new WAN RA/DHCPv6 immediately on every reconnect. Also, it seems not to send an RA on the LAN again for some minutes. This means there is a significant gap in IPv6 availability if there is a PPP drop from any reason.

Date Reported

2015-02-19

Updates

2015-02-19 In hand with ZyXEL.

Resolution

None yet.

MLD snooping

Issue Description

There is no way to enable MLD snooping on the LAN interface group without also enabling the router's Router Advertisement feature. This contrasts to IPv4, where I can disable the router's DHCP server but still enable IGMP snooping.

Date Reported

2015-03-06

Updates

None yet.

Resolution

None yet.

PPPoE Session-ID caching bug (In Bridge mode)

Issue Description

Last year we had an problem with Huawei FTTC modems, the standard ones that Openreach supply The bug appears to be that the modem manages to "blacklist" some UDP packets after a PPP restart. Typically this affects VPN tunnels. The short term fix is to unplugged and plugged back in!

We now have what looks to be the same fault on the ZyXELs - both on ADSL and VDSL.

When a PPPoE session finishes and a new one starts, ethernet frames containing IP packets with the same source and destination IP and port combination that were used in the previous session are received with the PPPoE Session-ID from the earlier session.

This affects long running sessions using protocols which use the same source port for all communications. This includes IPsec and (in some circumstances) SIP.

Our understanding of this, having talked to Huawei last year to get a very similar bug fixed is that the problem is with the packet accelerator feature in the Broadcom chipset. It is caching frame headers including the PPPoE Session-ID, but not checking if the Session-ID is the same when searching for the entry in the cache for subsequent packets. Unplugging the ethernet cable from the VMG1312 momentarily resolves the problem - that action must trigger a cache flush in the Broadcom chipset.

Possible fixes would be to either not store the Session-ID in the packet accelerator cache at all, or to check the Session-ID in addition to the IP and ports when searching the cache. A workaround would be to disable the packet accelerator.

Date Reported

2015-05-06

Updates

2015-05-06 - Escalated with ZyXEL/Broadcom 2015-05-15 - ZyXEL staff came to AAISP offices and we demonstrated and discussed the problem

Resolution

None yet.

QoS Issues RESOLVED

Issue Description

The QoS and traffic limiting features have the potential to be quite useful. However, the default QoS settings have problems if there is a large rsync (over ssh) upload in progress in that DNS queries time out. We have some QoS notes on ZyXEL_VMG1312-QoS.

Date Reported

2015-05-08

Updates

2015-05-15 A suitable configuration has been found

Resolution

Disabling default classes, and enabling QoS on packet length seems an all-round good solution

Template to use for new problems

Issue Title

Issue Description

Description of Issue.

Date Reported

2015-00-00

Updates

None yet.

Resolution

None yet.