CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Note: IP addresses are configured on dialer interfaces instead of the physical interfaces.
- With DDR dialer profiles configuration, a dialer interface is created for each remote site.
The dialer string command is used instead of the dialer map command since there is only one
remote site associated with each dialer interface. All dialer interfaces reside in different subnets,
which is like having virtual point-to-point links to each remote site.
- DDR dialer profiles configuration explanations:
1) Each ip route command points to a different next-hop address in different subnet.
2) There are 2 different ACLs as different dialer-list commands were created for each site.
3) The 2 different virtual dialer interfaces contain the commands for dialing to each site.
4) The name of a remote router which was configured as a parameter in the dialer-map
command is replaced with the dialer remote-name {name} interface subcommand.
5) The dialer interface 2 is configured to use a 56kbps B channel with a dialer class.
6) Dialer interfaces are logical and not physical, hence are unable to dial an actual call.
The dialer pool logic associated with a dialer interface will pick an available B channel from
a dialer pool when initiating a call.
7) The 2 BRI interfaces (total 4 B channels) are configured with their corresponding SPIDs, and
are associated to a pool with the dialer pool-member 1 interface subcommand.
Multilink PPP (MLP / MLPPP) Configuration
- It allows the creation of multiple links between routers, which traffic can be load balanced upon.
- Load balancing over parallel links without MLPPP is unpredictable and can be underutilized,
as the Cisco routers default switching mode – fast switching would send all packets destined to
the same IP address over the same link. Whenever some high volume data is being transmitted to
a single IP address, the packets would only be transmitted over a same single link.
- A PC can dial 2 ISDN B channels instead of one for faster connection. MLPPP breaks or
fragments each packet into 2 equal-sized packets, sends each fragment across each link, and
reassembles them back at the other end of the link.
- The dialer load-threshold {load} [inbound | outbound | either] interface subcommand
defines when to bring up the 2nd B channel. The load threshold range is 1 – 255, where 255 tells
the BRI to bring up the 2nd B channel only when the 1st channel is 100% loaded. The second
parameter is inbound, outbound, or either. It calculates the actual load on the interface either on
inbound traffic, outbound traffic, or either direction. The default is outbound.
Note: Multilink PPP is also referred as Bandwidth on Demand (BoD).
- PPP Multilink configuration:
Router(config)#int bri0
Router(config-if)#ppp multilink
Router(config-if)#dialer load-threshold 190 either
- Ex: The dialer load-threshold 190 either interface subcommand tells the BRI interface to
bring up the 2nd B channel if either the inbound or outbound traffic load excesses 75%.
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