Document ID: 15049
Contents
Introduction
Using the DNS Scripted Keepalives Configuration show Command Outputs Related Information
Using the DNS Scripted Keepalives Configuration show Command Outputs Related Information
Introduction
With the Cisco WebNS Software Releases 4.0 and later, customers have the ability to use scripted keepalives for nonstandard or specialized services, such as Domain Name System (DNS).
Because DNS queries are User Datagram Protocol (UDP)-based, you must configure a source group on the Content Services Switch (CSS) so that the responses from the DNS server appear to come from the same address from which the queries were originally sent (most likely the Virtual IP (VIP) address). When you activate this source group, the DNS scripted keepalives fail to work because the response to the keepalive query goes through Network Address Translation (NAT), causing the CSS to receive a response from a different IP address than the one to which you originally sent the request.
This configuration was developed and tested using the software and hardware versions below.
- All CSS platforms (CSS11000 and CSS11500)
- Cisco WebNS Software Releases 5.0 and later (scripted keepalives were not added until Release 4.0)
The information in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command on before using it.
Network Diagram
Using the DNS Scripted Keepalives
Tips for using the DNS scripted keepalives:
- Access to Internet Domain Name System Root Servers is required for successful implementation of DNS scripted keepalives.
- The service IP address has no bearing on the DNS service at all. Any address can be entered and it does not effect the state, however, an address must be entered or a "bad IP address" error appears.
- The argument for the script must be either the IP address or the hostname of the DNS server you want to check. It is typically the IP address configured on the service.
- The script is hard-coded to resolve www.cisco.com. It does not matter if the DNS server can resolve this address or not, as long as a DNS response comes back that the service is alive. This keepalive is only testing if a DNS server can respond to a query, not if it can resolve a specific name. The script queries from the CSS to DNS internal servers keep track of the availability of the DNS servers.
| CSS ap-kal-dns Script |
|---|
!no echo !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! Filename: ap-kal-dns ! Parameters: DNS_Server ! |
.
! If DNS servers cannot respond to a query, then you need to create an ACL with this logic:
- Anything sourced from one of the DNS servers destined for the CSS (circuit Virtual LAN (VLAN) IP address) bypasses all content rules and source groups.
- Other traffic sourced from the DNS servers goes through the configured source group.
Configuration
show Command Outputs
Samples of show command output:
show keepalive
52-css150-4# show keepalive Keepalives: Name: AUTO_nexthop00002 Index: 0 State: Alive Description: Auto generated for service nexthop00002 Address: 200.1.1.1 Port: Any Type: ICMP Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: nexthop00002 Name: AUTO_DNS1 Index: 1 State: Down Description: Auto generated for service DNS1 Address: 10.1.1.1 Port: Any Type: SCRIPT ap-kal-dns Script Arguments: "10.1.1.1" Script Error: Script error in line: 41 !--- Note: This service has no access to root servers, which causes the error.
Script Run Time: 4 seconds Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: DNS1 Name: AUTO_DNS3 Index: 2 State: Alive Description: Auto generated for service DNS3 Address: 10.1.1.3 Port: Any Type: SCRIPT ap-kal-dns Script Arguments: "10.1.1.3" Script Error: None !--- Note: This service has access to Internet root servers. Script Run Time: 0 seconds Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: DNS3 Name: AUTO_DNS4 Index: 3 State: Alive Description: Auto generated for service DNS4 Address: 10.1.1.4 Port: Any Type: SCRIPT ap-kal-dns Script Arguments: "10.1.1.4" Script Error: None Script Run Time: 0 seconds Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: DNS4 Name: AUTO_Router1 Index: 4 State: Down Description: Auto generated for service Router1 Address: 200.1.1.1 Port: Any Type: ICMP Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: Router1 Name: AUTO_DNS2 Index: 5 State: Down Description: Auto generated for service DNS2 Address: 10.1.1.2 Port: Any Type: SCRIPT ap-kal-dns Script Arguments: "10.1.1.2" Script Error: Script error in line: 41 Script Run Time: 4 seconds Frequency: 5 Max Failures: 3 Retry Frequency: 5 Dependent Services: DNS2 52-css150-4#
show keepalive-summary
52-css150-4# show keepalive-summary Keepalives: AUTO_nexthop00002 State: Alive 200.1.1.1 AUTO_DNS1 State: Down 10.1.1.1 AUTO_DNS3 State: Alive 10.1.1.3 AUTO_DNS4 State: Alive 10.1.1.4 AUTO_Router1 State: Down 200.1.1.1 AUTO_DNS2 State: Down 10.1.1.2
show service summary
52-css150# show service summary
Service Name State Conn Weight Avg State
Load Transitions
AUTO_DNS1 Down 0 1 2 0
AUTO_DNS3 Alive 0 1 2 1
AUTO_DNS4 Alive 0 1 255 1
AUTO_DNS2 Down 0 1 255 0
Related Information
| Updated: Jan 31, 2006 | Document ID: 15049 |