Limitations; Performance - Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010 Configuration Manual

JUNOSe 11.1.x Link Layer Configuration Guide
L2TP on an LNS processes the received Proxy Authen AVPs as described in L2TP
Proxy Authenticate Extensions for EAP draft-ietf-l2tpext-proxy-authen-ext-eap-01.txt
(December 2006 expiration).

Limitations

EAP is subject to internal limits. When the E Series router acts as a pass-through
between the backend authentication server and the peer, EAP packets traverse the
controllers within the router. The size of EAP packets and fragments tends to be
larger than the buffer exchange limit 1450 bytes between the controllers. This
intercontroller buffer exchange limit is tuned for the optimal system performance
and scalability; also, when stacked over L2TP on LNS, it prevents PPP control packets
from causing IP fragmentation and reassembly on the Ethernet downlink. Hence, if
EAP is configured as a PPP authentication protocol, then EAP packet or fragment
size is affected by the intercontroller buffer exchange limit as follows:
The MTU value is passed to RADIUS in an Access-Request packet by means of the
Framed-Mtu attribute.

Performance

When EAP is configured on the router, it affects the performance and scalability of
PPP in terms of round-trip packet exchanges, negotiations, EAP server requirements,
and EAP client requirements. For information on the number of PPP interfaces
supported with EAP, see the Link Layer Maximums tables in Appendix A, System
Maximums, of the current JUNOSe Release Notes.
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Overview
The MRU value advertised by JUNOSe in the LCP request packet takes the lowest
of the following values:
the lower layer MRU minus the PPP overhead
the configured MRU
1450 bytes
The MTU value is initialized by JUNOSe to the lowest of the following values:
the lower layer MTU minus the PPP overhead
the peer MRU
1450 bytes