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22-44
Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 22 Configuring Multilink Point-to-Point Protocol Connections
Verifying and Monitoring MLP Connections
Bundle Counters and Link Counters
When you enter the show interface command on an MLP bundle interface and on all of its member link
interfaces, you might expect the counters on the bundle to be equal to the sum of the counters for all of
the link interfaces. However, this is not the case.
The statistics for the various interfaces reflect the data that actually goes through those interfaces. The
data that goes through the bundle is different from the data going through the links. All of the traffic at
the bundle level does eventually pass through the link level, but it is not in the same format. In addition,
links also carry traffic that is private to that link, such as link-level keepalives.
The following list describes some of the reasons link-level and bundle-level counts might be different
(ignoring the link-private traffic):
• Multilink fragmentation might be occurring. A single packet at the bundle level becomes multiple
packets at the link level.
• Frames at the bundle level include only bundle-level encapsulation, which consists of a 2-byte PPP
header (or 1-byte header under some circumstances).
• Frames at the link level include link level encapsulation bytes, which include all forms of
media-specific encapsulation and framing. This information includes headers and trailers for
High-Level Data Link Control (HDLC) and PPP over ATM. The link-level encapsulation bytes also
include multilink subheaders (for example, sequence numbers), if they are used.
Note Multilink subheaders are not part of the packet encapsulation because it exists at the bundle
level. Multilink subheaders are part of the encapsulation that is added to fragments before
placing them on the link; they are not added to the network-level datagrams (for example, IP
packets) before sending them to the fragmentation engine.
Because of the factors listed above, the counts on the links can be greater than the counts on the bundle.
The link level has a great deal of overhead that is not visible at the bundle level.
Verification Examples for MLP Connections
This section provides the following verification examples:
• Verification Example for the show interfaces multilink Command, page 22-44
• Verification Example for the show ppp multilink Command, page 22-45
• Verification Example for the show interfaces multilink stat Command, page 22-46
Verification Example for the show interfaces multilink Command
Example 22-12 shows sample output for the show interfaces multilink command. In the example,
configuration information and packet statistics display for the MLP bundle 8.
Example 22-12 Sample Output for the show interfaces multilink Command
Router# show interfaces multilink 8
Multilink8 is up, line protocol is up
Hardware is multilink group interface
Internet address is 10.1.1.1/24
MTU 1500 bytes, BW 15360 Kbit, DLY 100000 usec, rely 255/255, load
1/255
Encapsulation PPP, crc 16, loopback not set