}
}
}
For NxT1 bundles using MLPPP, the byte-wise load balancing used in
multilink-encapsulated queues is superior to the flow-wise load balancing used in
nonencapsulated queues. All other considerations are equal. Therefore, we recommend
that you configure all queues to be multilink encapsulated. You do this by including the
fragment-threshold statement in the configuration. You use the multilink-class statement
to map a forwarding class into a multiclass MLPPP (MCML). For more information about
MCML, see “Configuring Multiclass MLPPP on LSQ Interfaces” on page 518. For more
information about fragmentation maps, see Configuring CoS Fragmentation by Forwarding
Class on LSQ Interfaces.
When a packet is removed from a multilink-encapsulated queue, the software gives the
packet an MLPPP header. The MLPPP header contains a sequence number field, which
is filled with the next available sequence number from a counter. The software then
places the packet on one of the N different T1 links. The link is chosen on a
packet-by-packet basis to balance the load across the various T1 links.
If the packet exceeds the minimum link MTU, or if a queue has a fragment threshold
configured at the [edit class-of-service fragmentation-maps map-name forwarding-class
class-name] hierarchy level, the software splits the packet into two or more fragments,
which are assigned consecutive multilink sequence numbers. The outgoing link for each
fragment is selected independently of all other fragments.
If you do not include the fragment-threshold statement in the fragmentation map, the
fragmentation threshold you set at the [edit interfaces interface-name unit
logical-unit-number] hierarchy level is the default for all forwarding classes. If you do not
set a maximum fragment size anywhere in the configuration, packets are fragmented if
they exceed the smallest MTU of all the links in the bundle.
Even if you do not set a maximum fragment size anywhere in the configuration, you can
configure the maximum received reconstructed unit (MRRU) by including the mrru
statement at the [editinterfaceslsq-fpc/pic/port unit logical-unit-number] hierarchy level.
The MRRU is similar to the MTU, but is specific to link services interfaces. By default the
MRRU size is 1500 bytes, and you can configure it to be from 1500 through 4500 bytes.
For more information, see “Configuring MRRU on Multilink and Link Services Logical
Interfaces” on page 516.
When a packet is removed from a nonencapsulated queue, it is transmitted with a plain
PPP header. Because there is no MLPPP header, there is no sequence number information.
Therefore, the software must take special measures to avoid packet reordering. To avoid
packet reordering, the software places the packet on one of the N different T1 links. The
link is determined by hashing the values in the header. For IP, the software computes the
hash based on source address, destination address, and IP protocol. For MPLS, the
software computes the hash based on up to five MPLS labels, or four MPLS labels and
the IP header.
For UDP and TCP the software computes the hash based on the source and destination
ports, as well as source and destination IP addresses. This guarantees that all packets
Copyright © 2017, Juniper Networks, Inc.522
ACX Series Universal Access Router Configuration Guide
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