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 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.
For more information on document conventions, refer to the Cisco Technical Tips Conventions.
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
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 two entries.
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
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.