Mlppp Link Selection; Configuring Multilink Ppp - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - LINK LAYER CONFIGURATION GUIDE 2010-10-13 Configuration Manual

MLPPP Link Selection

Copyright © 2010, Juniper Networks, Inc.
system determines that the remote system does not support multilink PPP and it
terminates the link without negotiation.
NOTE: The router does not bring up a link if the MRU value received from
a peer device differs from the MRRU value received from the peer.
Short sequence number (SSN) header format option (not currently supported)—The
SSN option indicates that the transmitting router wants to use a short sequence number
(12 bits) in the MLPPP header rather than a long sequence number (24 bits). The router
currently supports only long sequence numbers.
Endpoint discriminator option—The endpoint discriminator option identifies the router
transmitting the packet. If the receiving router determines that packets on another link
have the same endpoint discriminator option, this link must be joined to that bundle.
If the receiving router determines that no packets on other links have the same option,
the receiving router must create a new bundle from this link.
The endpoint discriminator is generated internally; you cannot configure it. The endpoint
discriminator option is the same for all links on one end of the bundle; at the other end,
all links also share a common endpoint discriminator. The two endpoint discriminators
are different if the MLPPP bundle is set up between two E Series routers.
By default, E Series routers use a round-robin algorithm to select the link on which to
transmit data on an MLPPP interface. The round-robin link selection method applies to
both best-effort packets, such as data, and non-best-effort (high-priority) packets, such
as voice and video. Best-effort packets are encapsulated with an MLPPP header that
contains a sequence number, whereas non-best-effort packets are encapsulated with
a PPP header that does not contain a sequence number.
The member links in an MLPPP bundle can experience different queuing delays due to
the volume of traffic transmitted on the MLPPP interface. These delays can cause packets
to arrive out of order at the remote router. The effect of such delays differs for best-effort
packets and non-best effort packets, as follows:
For best-effort packets that arrive out of order from the E Series router, the remote
router can use the sequence number to reorder and forward the packets in the correct
order, regardless of the order in which the packets were received.
For non-best-effort packets that arrive out of order from the E Series router, the lack
of a sequence number prevents the remote router from being able to determine the
correct order in which to forward the packets. This can cause problems with applications
that require high-priority voice and video traffic transmitted on MLPPP interfaces to
be received in the same order transmitted by the peer applications.
To ensure that the E Series router maintains the proper packet order when transmitting
non-best-effort traffic, you can use the ppp hash-link-selection command to enable
use of a hash-based algorithm to select the link on which the router transmits high-priority
packets on an MLPPP interface.
Chapter 9: Configuring Multilink PPP
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