MITnet - Core Infrastructure Services

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Time (NTP/SNTP):

IS&T makes available a time service on MITnet for systems and devices requiring clock synchronization. The time servers support both NTP and SNTP. Depending on the capabilities of the client, IS&T recommends configuring systems/devices to communicate with the time servers as follows:

Note: It is recommended to use hostnames whenever possible rather than hardcoding IP addresses in the configuration.

• Devices that support true NTP will require minclock (N=3) sources, but should be configured to use more for redundancy (N+1=4, N+2=5, ...). IS&T maintains 5 time servers (time-1, time-2, time-3, time-4, time-5) on MITnet to support redundancy.

• Devices whose configuration only supports one or two time servers should be configured to use "time-a" and "time-b". Devices that use less than 3 time servers can detect when a time server becomes unavailable, but not when a time server reports an incorrect time. Thus, to protect against "falsetickers", these clients should not directly query a stratum-1 time server. Configuring clients as described above will mitigate this issue.

• NTP broadcast is enabled on the Building-Management-System (BMS) subnets, but currently not enabled elsewhere.

Domain Name System (DNS):

IS&T maintains 3 DNS servers available to systems on MITnet for hostname resolution. These DNS servers are:

• ns1 = 18.0.70.160
• ns2 = 18.0.72.3
• ns3 = 18.0.71.151

The servers are authoritative for the following domains and will recursively resolve queries for records outside of these domains:

• mit.edu.
• n.18.in-addr.arpa. {n = 0..31 - with some exceptions}
• n.10.in-addr.arpa. {n = 0..255}

The MITnet (internal) view of the "mit.edu." domain differs from the Internet's (external) view such that hosts with private (10-net) IP addresses are not published in the external view.