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MLP is controlled by the
addition of a two-, four-, or eight-byte sequencing header in the
PPP frame that indicates sequencing for the fragments.
MLP Packet Header
RFC 1990 provides for only
four-byte headers. The first fragment of a multilink packet in PPP
has two headers, one for the fragment, followed by the header for
the packet itself.
During PPP negotiation, some
hardware platforms could use different header lengths for MLP,
causing potential problems. Please check with the specific platform
documentation if you have problems with MLP.
Transmission channels in the bundle need not
be the same types. Asynchronous and synchronous links, for example,
can be used to simultaneously transmit fragments of one datagram.
During the PPP LCP option negotiation, a
system indicates to its peer that it is willing to use multilink by
sending the MRRU option as part of the initial LCP option
negotiation. Multilink systems must be able to do the following:
- Combine multiple physical
links into one logical link (bundle)
- Receive and reassemble
upper-layer protocol data units (PDUs)
- Receive PDUs of a negotiated
size
The ppp multilink
command activates
multilink on an interface:
Router(config-if)#ppp
multilink
The following shows an example of the show
ppp multilink command. At the bottom of the output, you can see
the exact number of channels participating in the bundle:
Router#show ppp multilink
Bundle rudder, 3 members, first
link is BRI0: B-channel 1
0 lost fragments, 8 reordered,
0 unassigned, sequence 0x1E/0x1E rcvd/sent
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