Configurable MTU Size

Configurable MTU on per network-interface basis enables the user to set a different MTU on each network interface. It also enables the user to set a system wide default MTU for IPv6 and IPv4 network interfaces. System wide defaults can be set in system-config configuration object by setting ipv6-signaling-mtu or ipv4-signaling-mtu. Defaults are 1500 for both IPv6 and IPv4.

These settings can be overwritten for each network interface by setting signaling-mtu in network-interface configuration object. Default is 0 – meaning use the system wide MTU.

This feature applies to all Signaling packets generated by the Oracle® Enterprise Session Border Controller. All UDP packets greater than the MTU will be fragmented. For all TCP connections we advertise MSS (Maximum Segment Size) TCP option in accordance with the configured MTU. MSS option is sent in SYN and SYN/ACK packets to let the other side of the TCP connection know what your maximum segment size is. This ensures that no TCP packet is greater than the configured MTU.

MTU settings do not apply to media packets.
UDP: MTU settings apply only to packets sent by the Oracle® Enterprise Session Border Controller. The Oracle® Enterprise Session Border Controller will continue to process received packets even if they exceed to the configured MTU.
Security Phy (IPsec) hardware only; We subtract 100 bytes from the configured MTU to allow for extra headers added by security protocols. This happens even when Security Phy (IPsec) is in clear mode (no security is being applied). Due to hardware limitations of the Security Phy (IPsec) it only allows one MTU per physical port. The maximum MTU of all network interfaces on a given physical port will be used as the MTU for that physical port.
The Call Recording feature is where we make a copy of a packet, encapsulate it in an IP-in-IP header and send it to a configured Call Recording Server (CRS). When Call Recording is enabled, to allow space for IP-in-IP encapsulation we reduce the MTU of the original packets to be to be the lesser of the two options listed below.
- Original Destination network MTU minus size of IP-in-IP header.
- CRS network interface’s MTU minus size of IP-in-IP header.
  Note:
  This will ensure that the traffic sent to the CRS will be within the MTU constraints of CRS’ network-interface.