Solutions

How does PacketWise work with dynamic DNS?

Solutions ID:    KB2046
Version:    2.0
Status:    Published
Published date:    03/02/2009
Updated:    04/22/2009
 

Problem Description

One of the powerful features of PacketWise is its ability to classify traffic by dynamic DNS name, and to keep up with address changes even if DHCP or other dynamic addressing schemes are in use.

Resolution

Many servers use multiple or shifting IP addresses. For instance, a DNS lookup of www.cnn.com typically will return as many as 23 different IP addresses. PacketWise keeps track of all of the IP addresses associated with a DNS name, even as they change. Similarly, many organizations will bring backup database servers online for an application while doing maintenance or crash recovery. Because PacketWise is application-aware of dynamic DNS, it will observe that a new server at a new IP address is now handling transactions for "peoplesoft.packeteer.com" and continue applying policies correctly. Without this capability, IS networking staff would have to log into every QoS device and manually change the policies every time a new application server came online.

While user-based policies are often touted in QoS device literature, these are typically assigned by static IP address. Unfortunately, most organizations use dynamic IP address assignment schemes because of the much lower administration costs. Again, PacketWise's awareness of changing DNS entries allows it to keep up with the latest IP address that is associated with a user name, so that a policy for bob_smith.packeteer.com will work regardless of which IP address the DHCP server has given him today.

How can I look deeper into the DNS process if I am not getting the expected results?

The dns lookup hostname command displays a list of addresses, and will show the canonical name, if different from the query name.

For example:

10.7.51.100# dns lookup microsoft.com

Please wait, the hostname 'microsoft.com' is being resolved.........
lookup result:
query name: microsoft.com
canonical name: microsoft.com
address: 207.46.197.100
address: 207.46.197.102
address: 207.46.197.113
address: 207.46.230.218
address: 207.46.230.219
address: 207.46.230.220

10.7.51.100# dns lookup www.xyz.com

Please wait, the hostname 'www.xyz.com' is being resolved.........
lookup result:
query name: www.xyz.com
canonical name: www.xyz.com
address: 199.26.172.28

The dns trace command is a useful debugging aid that will cause the resolver to spill out an accounting of its activities:

10.7.51.100# dns trace

DNS Tracing is on

10.7.51.100# dns lookup foo.com

Please wait, the hostname 'foo.com' is being resolved.........;; res_querydomain(foo.com, , 1, 1)
;; res_query(foo.com, 1, 1)
;; res_mkquery(0, foo.com, 1, 1)
;; res_send()
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31477
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; foo.com, type = A, class = IN ;; Querying server (# 1) address = 40.1.1.10
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 31477
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0
;; foo.com, type = A, class = IN
foo.com. 1D IN A 208.191.14.250
foo.com. 1D IN NS ns2.meridian-ds.com.
foo.com. 1D IN NS ns1.meridian-ds.com.

lookup result:
query name: foo.com
canonical name: foo.com
address: 208.191.14.250

This output will be comfortably familiar to users of the BSD BIND resolver, from which this resolver is derived.

How can I see what addresses PacketWise has currently resolved a dynamic DNS name to?

The class show command shows the name/address mappings, including address lists. Here is an example:

PacketShaper# class show i

Traffic class: /Inbound/i
Partition: /Inbound
flags:
Current guaranteed rate 0 excess rate 0
tspecs:
[2 ] inside host abc.com(204.202.128.40) any port IP
outside any host any port
[4 ] inside host lasdkjf.com.() any port IP
outside any host any port
[5 ] inside host 1.2.3.4() a


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