What
is Multilink PPP?
This is a standard protocol that
allows the aggregation of PPP links into a single PPP link. The bundled links
can be of any type, ISDN, T1, or any other type that supports the basic PPP
protocol. The multilink configuration must be done on both sides of the link,
which implies that the different links must connect the same two equipment.
Topology
For the demonstration How to Configure Multilink PPP Connections for Serial interfaces, I use here
two routers interconnected by two serial links. The goal is to combine them
into a Multilink interface that will then be configured as any interface.
How to Configure Multilink PPP Connections for Serial interfaces
To configure this multilink PPP, you
have to go through two major steps:
- Creating the Multilink virtual interface
- Configure the serial interfaces to be integrated into the bundle.
Configuration
on R1
R1 # configure terminal
!!!! Creating the
Multilink interface !!!!
R1 (config) #interface multilink 1
R1 (config-if) # ppp
multilink
R1 (config-if) # ppp
multilink group 1
R1 (config-if) #ip address 192.168.0.1
255.255.255.252
R1 (config-if) #exit
R1 (config) #
!!!! Integration of the s0
/ 0 interface in the bundle
R1 (config) #interface serial 0/0
R1 (config-if) #encapsulation ppp
R1 (config-if) # ppp
multilink
R1 (config-if) # ppp
multilink group 1
R1 (config-if) #no shutdown
R1 (config-if) #exit
R1 (config) #
!!!! Integration of the s0
/ 1 interface in the bundle
R1 (config) #interface serial 0/1
R1 (config-if) #encapsulation ppp
R1 (config-if) # ppp
multilink
R1 (config-if) # ppp
multilink group 1
R1 (config-if) #no shutdown
R1 (config-if) #exit
R1 (config) #
Among the important details ... Of
course, the multilink group number specified in the interfaces configuration
must match. As this configuration shows, the interfaces S0 / 0 and s0 / 1 are
not addressed. They serve only as physical liaison. Addressing is done on the
multilink interface.
Note also that if you need to use a
routing protocol, a NAT process, or any other element that would interfere with
the routing of this interface, the multilink interface should be referenced.
Configuration
on R2
R2 # configure terminal
!!!! Creating the
Multilink interface !!!!
R2 (config) #interface multilink 1
R2 (config-if) # ppp
multilink
R2 (config-if) # ppp
multilink group 1
R2 (config-if) #ip address 192.168.0.2
255.255.255.252
R2 (config-if) #exit
R2 (config) #
!!!! Integration of the s0
/ 0 interface in the bundle
R2 (config) #interface serial 0/0
R2 (config-if) #encapsulation ppp
R2 (config-if) # ppp
multilink
R2 (config-if) # ppp
multilink group 1
R2 (config-if) #no shutdown
R2 (config-if) #exit
R2 (config) #
!!!! Integration of the s0
/ 1 interface in the bundle
R2 (config) #interface serial 0/1
R2 (config-if) #encapsulation ppp
R2 (config-if) # ppp
multilink
R2 (config-if) # ppp
multilink group 1
R2 (config-if) #no shutdown
R2 (config-if) #exit
R2 (config) #
The configuration is almost
identical, of course. Note that the number of the multilink interface must not
necessarily be the same as on the other router. The same applies to the
multilink group number. There is also no relationship between the number of the
multilink interface and the group number.
Communication
test
R1 # ping 192.168.0.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.2,
timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip
min / avg / max = 1/4/12 ms
R1 #
No surprise ... everything works!
Checking
the configuration
R1 # show interface serial 0/0
Serial0
/ 0 is up, line protocol is up
Hardware is GT96K Serial
MTU
1500 bytes, BW 1544 Kbit / sec, DLY 20000 usec,
Reliability 255/255, txload 1/255, rxload
1/255
PPP Encapsulation, LCP Open, multilink Open
Link is a member of Multilink bundle Multilink1 ,
loopback not set
Keepalive set (10 sec)
CRC
checking enabled
Last
input 00:00:09, output 00:00:03, output hang never
Last
clearing of "show interface" counters 00:13:07
Input
tail: 0/75/0/0 (size / max / drops / flushes); Total output drops: 1
Queuing
strategy: weighted fair [suspended, using FIFO]
FIFO
output queue 0/40, 0 drops
5
minute input rate 0 bits / sec, 0 packets / sec
5
minute output rate 0 bits / sec, 0 packets / sec
163
packets input, 5310 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0
throttles
0 input
errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
183
packets output, 5770 bytes, 0 underruns
0
output errors, 0 collisions, 6 interface resets
0
unknown protocol drops
0
output buffer failures, 0 output buffers swapped out
0
carrier transitions
DCD =
up DSR = up DTR = up RTS = up CTS = up
R1 #
The interface works well in PPP, and
is a member of the multilink group 1.
R1 # show interface multilink 1
Multilink1
is up, line protocol is up
Hardware is multilink group interface
Internet address is 192.168.0.1/30
MTU
1500 bytes, BW 3088 Kbit / sec , DLY 100000
usec,
Reliability 255/255, txload 1/255, rxload
1/255
PPP
Encapsulation, LCP Open, multilink Open
Open:
IPCP, CDPCP, loopback not set
Keepalive set (10 sec)
DTR is
pulsed for 2 seconds on reset
Last
input 00:00:31, output never, output hang never
Last
clearing of "show interface" counters 00:17:23
Input
tail: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0
Queuing
strategy: fifo
Output
tail: 0/40 (size / max)
5
minute input rate 0 bits / sec, 0 packets / sec
5
minute output rate 0 bits / sec, 0 packets / sec
29
packets input, 5944 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0
throttles
0 input
errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
29
packets output, 6266 bytes, 0 underruns
0
output errors, 0 collisions, 1 interface resets
0
unknown protocol drops
0
output buffer failures, 0 output buffers swapped out
0
carrier transitions
R1 #
Note here the bandwidth of the
interface that takes the combined value of the two physical interfaces (2x
1544kbits / s).
R1 # show ppp
multilink
Multilink1
Bundle name: R2 Remote Endpoint Discriminator: [1] R2 Local Endpoint Discriminator:
[1] R1 Bundle up for 00:26:33, total bandwidth 3088, load 1/255 Receive buffer
limit 24000 bytes, frag Timeout 1000 ms 0/0 fragments / bytes in reassembly
list 0 lost fragments / bytes, 0 lost received 0x5C received sequence, 0x5C
sent sequence Member links: 2 active, 0 not active (max not set, min Not set)
Se0 / 0, since 00:26:34 Se0 / 1, since 00:26:03 No inactive multilink
interfaces
R1
#
Here you find the state of the
multilink link. You will find the interfaces that are part of the bundle, as
well as information about the name of the remote equipment and counters for the
number of packets transmitted, destroyed, ...
Conclusion
The basic configuration of a
multilink PPP link is quite simple and intuitive. It also makes it possible to
increase the bandwidth of the link without making the topology more complex. Note
however that this is a very basic configuration, it is of course possible to
configure the authentication, or to set the distribution of the data on the
links.
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