This document explains how to allow a Cisco 700 router to bring up ISDN
due to HTTP traffic.
There are no specific requirements for this document.
The information in this document is based on these software and
The Cisco IOS® Software Release 4.4.2, and later.
Cisco 700 series routers (which includes 761, 775 and
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.
For more information on document conventions, refer to the
Technical Tips Conventions.
This section provides some background information about the netbios
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
SET IP FILTER TCP OUT DEST 0.0.0.0/0:137
SET IP FILTER UDP OUT DEST 0.0.0.0/0:53
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.
The workaround is to disable the filter and configure only the first
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
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