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Router - DLINK 320B

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Currently shipping hardware version

alt Dlink DSL-320B-Z1 modem, front view

At the time of writing, December 2017, the currently shipping hardware version of the DLink DSL-320B modem/router is the DSL-320B-Z1. Confusingly, in the past DLink has described several completely different modems as “DSL‑320B”. The following sections describe the DSL‑320B‑Z1 hardware.

Factory default IP, admin password

Factory default web admin interface
Username: admin
Password: admin


  • AAISP ships these devices for use as straight ethernet modems. Although they are capable of working as (buggy) routers, AA pre-configures them to work in bridge mode only, that is, in simple PPPoE modem-only mode, not operating as routers.

The modem’s admin web interface is quite insecure and in ‘router’ mode they have various critical security bugs, which is why we strongly suggest that customers never use them configured in ‘router’ mode. They are sold by AAISP as bridge-only. Older pre-Z1 modems, such as the now obsolete “-D1” model, were shipped with their reset buttons covered to protect them and prevent them from being reset!

  • If you reset a modem to the factory settings using the pin-in-hole technique, then it will not work at all as a straight PPPoE ethernet modem while it still has its factory defaults. The configuration must be altered before use. Ask AA support for help with this or see post-factory reset configuration instructions below.
  • No per-user or per-line login info or password configuration is required. Information concerned your ISP account or line-specific login and password is configured in your router, and the DLink modem doesn’t need these values.
  • The modem supports 1500 byte IP MTU/MRU (unlike the Router - ZyXEL P660R-D1) by using ethernet frames with a 1500+8=1508 byte payload. (Your router will also have to support RFC 4638 and 1500+8=1508 byte MTU/MRU as well though for this to be effective. Note that an MTU of 1500 is not supported by BT on 20CN lines.)
  • Important - BT 20CN lines: MTU 1500+8=1508 will not work on old BT 20CN lines because of BT’s limitations, nothing related to this modem.
  • The modems support the ADSL standards G.992.1/G.DMT (‘ADSL1’), G.992.3 (ADSL2) and G.992.5 (ADSL2+) and can either auto-detect the best mode or lock it to just one option. Annex M is supported. SRA is also supported.
  • VDSL2 is not supported, so these devices cannot be used with FTTC.
  • TR-069 is not supported by AA on these devices, so they cannot automatically be remotely configured, monitored or upgraded by AA.
  • It is vital that you not expose the LAN-side ethernet interface to users on the LAN unless all possible users and devices on the LAN are trusted, because of various critical security bugs in the modem in this respect. Because of such bugs, setting passwords on the modem’s admin web UI etc. is not enough. If your router happens to prevent LAN-internal users from accessing the modem then so much the better, otherwise your main router’s facilities, internal firewalling and access controls could be exploited. A firmware upgrade to release v1.06 or higher could well help fix security problems concerning access without any administrative login. Firmware v1.06
  • Chipset: The currently shipping DSL-320B-Z1 units (at the time of writing, December 2017) use an old but capable MediaTek/TrendChip chipset. The older “-D1” routers were Broadcom-based.
  • Incorrect manufacturer’s defaults: The default settings shown in the router’s web admin user interface show defaults that are very much sub-optimal. DSL bitswap is set to off by default according to the web admin user interface. These settings need to be amended - see following section.

Initial setup using the web admin interface

The manufacturer’s default settings shown in the router’s web admin user interface show defaults that are very much sub-optimal. It is important to enable the ‘bitswap’ option for best reliability and performance. (See also this discussion of bitswap.)

These settings need to be configured as follows:

‘ADVANCED’ (top horizontal navigation bar) > Advanced ADSL (lhs vertical navigation list)

  • Bitswap - enable (very important)
  • SRA - enable (for future-proofing, but currently has no effect as SRA is not supported by e.g. BT currently)

Performance tip for long lines: If you have an extremely long phone line (>60 dB downstream attenuation) and you have an ADSL2+ service, it is maybe worthwhile experimenting with setting the DSL mode/standard option to ‘ADSL 2’ (only) in the list of options, that is, taking ADSL2+ out of the list of allowed standards, as opposed to allowing the modem to use ADSL2+, to see if this restriction gives a performance improvement. It will be a long process to get a meaningful comparison with many restarts and many tests needed to confirm any possible performance difference between allowing and disallowing ADSL2+. If in any doubt always enable ADSL2+ or ‘auto' mode ie ADSL1/ADSL2/ADSL2+, where the modem will use ADSL2+ if the exchange’s DSLAM or MSAN supports ADSL2+ too. With one particular 65dB downstream attenuation line, no improvement was seen, but better results were seen on a somewhat shorter, better line.

After each reset to factory settings

After any reset to factory settings you will need to make the following change using the web admin user interface in order to get the device to work properly as a straight modem. (Factory default, and your own ip address set to something suitable in that same /24 subnet, username=admin, password=admin.) Go to “Setup” and “ADSL Setup” and there tick “Manual Setup”. Then tick “Bridge Mode”. The “Connection Type” should show “1483 Bridged IP LLC" and the VPI / VCI settings on that page should be set to VPI = 0, VCI = 38. See also article at bridge mode setup article at Dlink website. If your modem is accessible by users on the LAN, see the notes on security and access given earlier. Ideally consider using your router’s firewall capabilities if possible to block access to the modem. Failing that upgrade the firmware - see earlier notes - and set a suitable administrative password (see the Maintenance menu). Performance tip: the leaner PPPoEoEoA + RFC2684 [obsoletes RFC1483] section 6.2 + VC-MUX header option (“bridged PDUs: VC-MUX”) is always more efficient than or the same as the alternative “LLC” header option. Choose 1483 Bridged VC-MUX aka PPPoE VC-MUX in preference to LLC if your exchange supports it, for example if you are using a BT 21CN line or a TalkTalk line. If unsure, use PPPoE / 1483 Bridged IP VC-MUX if there are no problems, otherwise ask AA support. The actual effective speed improvement depends on the length of the packets being sent (because of the absorbing effect of ATM cell padding) and for some packet lengths the performance gain is zero. Following this you will then also need to make the configuration changes described in the previous section.

Resetting to factory settings

To reset the modem to factory settings, locate the reset button hole on the rear panel of the unit. With the modem powered on, use a paperclip to hold the button down and keep an eye on the status LED on the front of the unit. When the status LED goes off release the reset button and the modem will go through its reboot process. Wait about 30 seconds to access the modem. The default IPv4 address for the modem’s http admin user interface on the LAN is Your own IPv4 address will need to be in the same subnet and different from that of the modem, i.e. set to something in the range - .254, so perhaps use You can then log in to the web admin interface using a web browser at, username=admin, password=admin.


DLink DSL-320B-Z1 modem

The currently shipping (as of December 2017) DLink DSL-320B-Z1 modem, rear view


Rear view of obsolete ‑D1 modem

(The image below is of the older generation of routers.)

Rear view of obsolete pre-Z1 modem, showing blanked-off reset button