Troubleshooting and help

Information Technology Team > Troubleshooting and help

1 Wired network

1.1 The network has suddenly become inaccessible.

The network may suddenly become inaccessible in a networked environment. This problem is often caused by a network loop in the LAN; the entire subnet fails when both ends of the LAN cable are connected to a single switch. If the LAN cable has been reconnected or rearranged at around the failure occurrence time, check for a network loop. In many cases, this condition is caused by plugging an unused (not disconnected) cable in error. Keeping the room tidy facilitates determining cable condition and contributes to the prevention of the problem.

1.2 The network is inaccessible with the LAN cable connected to the information wall socket.

The School of Science network is divided into Department/Facility (or laboratory) subnets. The information wall socket in each room provides access to the subnet of the Department/Facility (or laboratory) the room user belongs to. If the room user has been changed or if the network has not been used in the room, settings must be reconfigured. Ask the Information Technology Team through the relevant Department/Facility administrator to reconfigure the settings.

1.3 It has suddenly become impossible to obtain an IP address.

An unauthorized DHCP server may be connected. In principle, the School of Science prohibits network users from installing NAT devices or Wi-Fi access points. Unauthorized installation of broadband routers or wireless routers (including Time Capsule) may interfere with obtaining an IP address across the entire Department/Facility subnet.

1.4 An IP address cannot be obtained.

Devices accessing the School of Science network must be properly managed. Devices managed under the School of Science host management system are automatically registered for Wi-Fi access. For the registration of devices managed by the Departments/Facilities, contact the relevant Department/Facility subnet administrator. For details, see the page Host management system.

1.5 No information wall socket is available.

At least one information wall socket is located in each room. If the socket cannot be found, do not hesitate to contact us. Information on the socket location will be provided for reference based on the room layout drawing.

1.6 The information wall socket has been relocated (added) in conjunction with interior work.

The network situation changes when the information wall socket has been relocated in conjunction with interior work on individual rooms. When performing interior work, obtain the work drawing from the contractor and submit it to the Information Technology Team. For the installation of additional information wall sockets, contact us in advance. It may be impossible to install additional sockets due to facility limitations. Follow the instructions given in 1.7.

1.7 Since two PCs access the network (or the existing information wall socket is in an inconvenient location), an additional information wall socket is required.

In principle, only one information wall socket is available in each room. While additional sockets may be provided for users accessing multiple networks (VLANs), a switch (hub) should be installed in the room when connecting multiple PCs to the network. Some rooms are equipped with multiple information wall sockets; however, not all sockets are connected to network devices, since the core network capacity is limited.

1.8 An individual not belonging to the School of Science uses a room in the School.

Security policies and incident response plans are in place on a Department/Facility basis. The University of Tokyo assumes that each individual uses the network in his/her Department/Facility. UTnet provides an inter-building VLAN service that allows individuals in a School of Science building to access networks used in other buildings. Application for the service should be made on UTnet by the UTnet staff in each Department/Facility.

2 Wi-Fi network

2.1 I do not know how to use the Wi-Fi network.

See the page Guide to using Wi-Fi.

2.2 No access point has been installed in the room.

Wi-Fi access points are spaced at proper intervals so that Wi-Fi covers all School of Science buildings. Wi-Fi access is available, even if no access point has been installed in the room. If the radio field intensity is extremely low due to access point locations (and if there is a user need for Wi-Fi access), a slight adjustment of access point locations may be considered. However, the addition of access points is difficult; since the narrow bandwidth of the 2.4 GHz band is shared, an excessively increased number of access points may result in radio interference, further degrading Wi-Fi performance.

3 Other services

3.1 External connection

The School of Science provides a VPN connection service and a SSL-VPN connection service for external access (e.g. from home). The SSL-VPN connection service is available to browse websites accessible only from within the School of Science network. The [[VPN connection service] is used to access internal servers by connecting to Department/Facility (or laboratory) subnets.

3.2 E-mail address

An e-mail address is assigned by each Department/Facility. Contact the relevant Department/Facility subnet administrator. For Department/Facility subnet administrators, see the page Network administrators (Japanese) (internal access only)”.

3.3 University-wide administrative systems

University-wide administrative systems are described on the University’s portal (Japanese). See the description of each system given by the related staff in the Department/Facility.

4 Contact

If you have any questions or inquiries, contact the Information Technology Team by e-mail. When making a request for investigation of network-related problems, provide the following information. Detailed information (user, MAC address, etc.) often helps to identify the cause of failure using log data stored on network devices. Your cooperation is appreciated.

Date/time
Place (room)
Information wall socket in use (for the wired LAN)
Terminal user (especially for Wi-Fi)
MAC address
Description of the problem
Measure attempted to address the problem