User guide

3-104 Packet Over SONET Module Installation and User Guide
Configuring the PoS Module
Jumbo Frame Support
The Extreme Networks implementation of PPP supports the Link Control Protocol
(LCP) maximum receive unit (MRU) option, which specifies the maximum number of
octets that a PPP information field can contain and still be received successfully. In the
Extreme Networks implementation, the advertised MRU size depends mainly on two
factors:
• Whether IPCP or BCP is enabled on the PoS port
• Whether jumbo frame support is enabled on the PoS port
If IPCP is configured on the port and jumbo frame support is not enabled, the Extreme
Networks implementation of PPP advertises an MRU of 1500 octets and requires that
the peer have an MRU of at least 1500 octets.
If BCP is configured on the port and jumbo frame support is not enabled, the advertised
MRU is 24 octets larger than in the corresponding IPCP case. The additional octets are
needed to accommodate the larger frame size associated with the bridged format, which
includes the MAC header. If VLAN tags are to be transmitted, the peer’s MRU must be
at least 1520 octets; otherwise, the peer’s MRU must be a minimum of 1516 octets.
If IPCP is configured on the port and jumbo frame support is enabled on the port, the
advertised MRU size in octets is calculated using the following formula:
(configured jumbo frame MTU – 22)
and the peer is also required to have an MRU at least this large.
If BCP is configured on the port and jumbo frame support is enabled on the port, the
peer’s MRU must be (configured jumbo frame MTU – 6) octets at a minimum, and at
least (configured jumbo frame MTU – 2) octets if VLAN tags are to be transmitted.
show ports {<portlist>} txerrors Augmented implementation: Only a subset of
the statistics displayed by this command are
applicable to PoS ports. The fields that do not
apply to PoS ports are displayed with values of
all zeroes.
Table 3-18: Changes to Port Commands (continued)
Command Description of Change