Allowing a Cisco 700 Router to Bring Up ISDN Due to HTTP Traffic

Introduction

This document explains how to allow a Cisco 700 router to bring up ISDN due to HTTP traffic.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software and hardware versions:

• The Cisco IOS® Software Release 4.4.2, and later.

• Cisco 700 series routers (which includes 761, 775 and 776).

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Netbios Filter

This section provides some background information about the netbios filter.

The Cisco IOS Software Release 4.4.2 (and later) for Cisco 700 series routers has the set netbios filter on command on by default for all the ISDN profiles, including the standard profile.

This netbios filter is used to prevent netbios packets from bringing up the ISDN B channel all the time. It is composed of these three entries:

• SET IP FILTER UDP OUT DEST 0.0.0.0/0:137-139 IGNORE

• SET IP FILTER TCP OUT DEST 0.0.0.0/0:137 IGNORE

• SET IP FILTER UDP OUT DEST 0.0.0.0/0:53 IGNORE

Drawback

The drawback of this filter is that an HTTP browser will never bring up the ISDN link. This is because User Datagram Protocol (UDP) traffic to Domain Name System (DNS) server port 53 is filtered.

Workaround

The workaround is to disable the filter and configure only the first two entries.

Example:

router> cd ProfileName
router:ProfileName> SEt NETbios FIlter OFf
router:ProfileName> SET IP FILTER UDP OUT DEST 0.0.0.0/0:137-139 IGNORE
router:ProfileName> SET IP FILTER TCP OUT DEST 0.0.0.0/0:137 IGNORE
router:ProfileName> 

Then, use the show ip filter command to verify this, as shown here:

   router:ProfileName> show ip filter
   IP Type Filter
   Profile ID Dir Type Action Addresses
   ----------------------------------------------------------
   ProfileName 1 OUT UDP IGNORE DST 0.0.0.0/0:137-139
   ProfileName 2 OUT TCP IGNORE DST 0.0.0.0/0:137
   IP Generic Filter
   Profile ID Dir Type Action Patterns

Note: As of Cisco IOS Software Release 4.4.3 for Cisco 700 series routers, the set netbios filter command has been adjusted so that it no longer contains the entry for UDP traffic on port 53.

     SET IP FILTER UDP OUT DEST 0.0.0.0/0:137-139 IGNORE    
     SET IP FILTER TCP OUT DEST 0.0.0.0/0:137 IGNORE

Related Information

• Access Dial - Technology Support Pages
• Technical Support - Cisco Systems