Cisco 1003 - 1003 Router Manual de usuario descargar pdf (Pagina 26)

11-26 Internetwork Design Guide

Tariff Management

SNMP Packets

Although SNMP can provide useful information about ISDN connections and how they are used,

using SNMP can result in excessive up time for ISDN links. For example, HP OpenView gathers

information by regularly polling the network for SNMP events. These polls can cause the ISDN

connections to be made frequently in order to check that the remote routers are there, which results

in higher ISDN usage charges. To control ISDN charges, the central site should ﬁlter SNMP packets

destined for remote sites over ISDN. Incoming SNMP packets from remote sites can still be

permitted, which allows SNMP traps to ﬂow to the SNMP management platform. That way, if an

SNMP device fails at the remote site, the alarm will reach the SNMP management platform at the

central site.

To control SNMP trafﬁc, create an access list that denies SNMP packets. The following is an

example of SNMP ﬁltering:

access-list 101 deny tcp any any eq 161

access-list 101 deny udp any any eq snmp

access-list 101 permit ip any any

dialer-list 1 list 101

Note The preceding example uses two access-list commands because the Layer 3 SNMP protocol

can be either TCP or UDP. If your network uses IPX SNMP, you must create a separate access list.

Banyan VINES, DECnet IV, and OSI Packets

Cisco IOS Software Release 10.3 introduces access lists for Banyan VINES, DECnet IV, and the

Open Systems Integration (OSI) protocol. When a dialer map is conﬁgured for these protocols,

access lists can be used to deﬁne interesting packets (that is, packets that will trigger the DDR link).

IPX Packets

You can use access lists to declare as uninteresting packets intended for the Novell serialization

socket (protocol number 0, socket number 457), RIP packets (protocol number 1, socket

number 453), SAP packets (protocol number 4, socket number 452), and diagnostic packets

generated by the autodiscovery feature (protocol number 4, socket number 456). Uninteresting

packets are dropped and do not cause connections to be initiated. For a sample IPX access list, see

the chapter “Using ISDN Effectively in Multiprotocol Networks” in the Internetworking Case

Studies publication.

Protocol-Speciﬁc Techniques

This section describes techniques that supplement snapshot routing and access lists for the following

protocols:

• IPX

• AppleTalk

IPX

IPX sends out several types of packets that, if not controlled, cause unnecessary connections: IPX

watchdog packets and SPX keepalive packets. In addition, NetWare includes a time synchronization

protocol that, if not controlled, causes unnecessary connections.

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Cisco 1003 - 1003 Router Manual de usuario Pagina 26