Path MTU Discovery
Path MTU Discovery Overview
The maximum transmission unit (MTU) size of a node is the largest packet the node can transmit. For a packet to successfully traverse the path from the source node to the destination node, the packet must be no larger than the smallest MTU size of all nodes on the path between the source and destination. This value is referred to as the path MTU. If a packet is larger than a link’s MTU size, it is likely that the link will drop it. Path MTU discovery checks the MTU on a network path between two nodes.
Path MTU discovery is enabled by default. We recommended leaving path MTU discovery enabled. Disabling path MTU discovery can have adverse affects on network stability.
Configure Path MTU Discovery on Outgoing TCP Connections
By default, path MTU discovery on outgoing TCP connections is enabled. To disable
path MTU discovery for IPv4, include the no-path-mtu-discovery
statement at the [edit system internet-options] hierarchy
level:
[edit system internet-options] no-path-mtu-discovery;
To reenable path MTU discovery on outgoing TCP connections, include the
path-mtu-discovery statement at the [edit system
internet-options] hierarchy level:
[edit system internet-options] path-mtu-discovery;
To disable and reenable path MTU discovery for IPv6, use the
ipv6-path-mtu-discovery and
no-ipv6-path-mtu-discovery statements.
Configure IP-IP Path MTU Discovery on IP-IP Tunnel Connections
By default, MTU discovery on outgoing IP-IP tunnel connections is enabled.
To disable IP-IP path MTU discovery, include the
no-ipip-path-mtu-discovery statement at the [edit
system internet-options] hierarchy level:
[edit system internet-options] no-ipip-path-mtu-discovery;
To reenable IP-IP path MTU discovery, include the
ipip-path-mtu-discovery statement at the [edit
system internet-options] hierarchy level:
[edit system internet-options] ipip-path-mtu-discovery;
Configure Path MTU Discovery on Outgoing GRE Tunnel Connections
By default, path MTU discovery on outgoing GRE tunnel connections is enabled. To
disable GRE path MTU discovery, include the
no-gre-path-mtu-discovery statement at the [edit
system internet-options] hierarchy level:
[edit system internet-options] no-gre-path-mtu-discovery;
To re-enable GRE path MTU discovery, include the
gre-path-mtu-discovery statement at the [edit
system internet-options] hierarchy level:
[edit system internet-options] gre-path-mtu-discovery;
To verify details of the path MTU on outgoing GRE tunnels, use the command
show interfaces (GRE).